Symposium NM05—Advances in Nanodiamonds for Sensing, Biomedical and Other Novel Applications

Optically addressable point-defects in wide band gap semiconductors, such as the nitrogen-vacancy center in diamond and divacancy complexes in silicon carbide offer a versatile platform for quantum technology. These localized point defects are intrinsically sensitive to the local changes in their charge, magnetic field, and crystallographic environment. As such, understanding the intricate interplay between quantum defects and their material hosts remains a critical step toward improving spin coherence, charge stability, and optical properties. Moreover, defect creation through means such as ion implantation inherently damages the local crystal structure, further motivating the need to understand lattice deformations at the nanoscale. Here, I will present work on developing methods to create, measure, manipulate, and localize coherent spins in diamond using growth synthesis methods with a specific effort in localizing defects in low-dimension materials. I will discuss recent advances in synthesizing a low-dimensionality diamond membrane defect host platform with deterministic integration of spin qubits and explore a scalable pathway towards bottom-up engineering of nanoscale diamond particles for quantum sensing applications. I will also describe advanced characterization techniques including synchrotron-based, strain-sensitive x-ray imaging to measure the local lattice strain within diamond and SiC. Combining these techniques with localized defect creation and other advanced defect imaging techniques provides a direct means to understand the local crystal environment surrounding the defects and offers a pathway for synthesizing, optimizing, and integrating point-defect-based quantum technologies.

Single-atom qubits are a potential architecture for quantum information systems, with one promising system being nitrogen-vacancy (NV) centers in nanodiamonds. Nanodiamonds offer many advantages for quantum systems, including chemical inertness, a tunable surface, and zero nuclear spin. NV centers produce strong single-photon photoluminescence, with a relatively long spin coherence time, which is beneficial for quantum communication. However, details of the qubit environment, such as location within the host lattice, bonding environment, and charge state, can strongly affect the qubit properties. In order to directly probe the NV centers in nanodiamonds, we use a scanning transmission electron microscope (STEM) with single-atom sensitivity for imaging, electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDS). Prior computational modeling has shown that the NV center in nanodiamond introduces a characteristic pre-edge defect feature on the C-K edge at 282.4 eV [1]. Although the corresponding feature at the N-K edge is too weak for observation in EELS, we can experimentally confirm the identity of C-K pre-edge peak with simultaneous EELS and EDS spectrum imaging. The ability to locate and study single NV centers in nanodiamond is an important first-step towards quantum device fabrication.
[1] S.L.Y. Chang et al. Nanoscale, 8, 10548 (2016).

Nitrogen-vacancy (NV) centers in fluorescent nanodiamonds (FND) have attracted immense interest due to their room-temperature emission, exceptionally high photo- and chemical stability, and excellent biocompatibility. Such outstanding properties have gifted NV centers broad application prospects in the fields like quantum sensing and biomedical diagnostic applications. However, the lack of precise understanding of the factors affecting NV optical properties (e.g., NV distribution, particle morphology, and surface properties of particles) limits its performance control and optimization. Therefore, an in-depth exploration of these factors is essential to further explore the potential of NV centers in FND.
Unlike most other fluorescent nanoparticles, FND samples typically contain a wide range of particle size and shape distributions. And, it has been reported that the same size (and same fabrication process) individual FND particles with NV centers can exhibit a 4-5-fold variation in photoluminescent (PL) intensity. The above characteristics bring a challenge to our study, namely, it is not feasible to only focus on particle structure information or to only measure the particle shape distribution.
To overcome this, a new correlative photoluminescence-transmission electron microscopy (PL-TEM) method has been developed. The method combines confocal PL microscopy with TEM imaging of the same sample region, offering direct and accurate optical properties and nanostructure correlation at the individual particle level while measuring statistically significant particle numbers.
Here, we perform a direct correlation between PL images and TEM montage maps of the same region of the sample. Morphological (size and shape) data and PL intensity/ lifetime of individual particles in the region were measured by bright-field TEM and confocal PL microscopy, respectively. High-resolution TEM, and high-energy resolution electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) were used to measure the surface properties of the FND particles. The FND sample used here is nominally 100 nm size FND (with NV) particles produced by ionization irradiation and high-temperature annealing, with two different surface treatments (acid treatment, molten salt treatment) for comparison.
PL-TEM correlation results also demonstrate the fluctuation of NV brightness in particles of the same size (volume). However, the particle morphological dependency of NV fluorescence is revealed after adding the three-dimensional shape of the particles into consideration. We found that flake-shape particles produced enhanced fluorescence: after normalizing the volume of FND particles and performing statistical analysis, the results showed that the relative brightness of thin, flake-shaped FND particles is several times higher than that of the thicker, three-dimensional-shaped particles. Furthermore, by comparing high-resolution measurements on particle surface with optical measurements, we found that this trend is robust to different surface oxidation treatments. Our theoretical calculations also support this finding. Such results offer new possibilities for fluorescence-optimized sensing applications of FND by controlling the particle thickness and shape.

Charge control of color centers in semiconductors promises opportunities for novel forms of sensing and quantum information processing. This presentation discusses recent work articulating confocal fluorescence microscopy and magnetic resonance protocols to induce and probe charge transport between discrete sets of engineered nitrogen-vacancy (NV) centers in diamond, down to the level of individual defects. In our experiments, a ‘source’ NV undergoes optically-driven cycles of ionization and recombination to produce a stream of photo-generated carriers, one of which we subsequently capture via a ‘target’ NV several micrometers away. We use a spin-to-charge conversion scheme to encode the spin state of the source color center into the charge state of the target, in the process allowing us to set an upper bound to carrier injection from other background defects. We attribute our observations to the action of unscreened Coulomb potentials producing giant carrier capture cross-sections, orders of magnitude greater than those typically attained in ensemble measurements. Besides their fundamental interest, these results open intriguing prospects for applications ranging from the use of free carriers to expose otherwise invisible point defects, to establishing a quantum bus to mediate effective interactions between paramagnetic defects in a solid-state chip.

Micro- and nano-sized diamond particles with color centers are some of the most promising candidates for sensing and imaging applications in biological, biomedical, and industrial fields. Traditionally, irradiated diamond particles are annealed at ca. 900 °C for 1-2 hours. During annealing, vacancies formed during irradiation become mobile, and their diffusion results in the formation of complexes with substitutional nitrogen to yield nitrogen-vacancy (NV) centers. Recent efforts explored the use of high temperature annealing (ca. >1,500°C) at short timescales (seconds to minutes). At these temperatures, the diffusion of nitrogen as well as vacancies can dramatically alter the constituent color centers in the diamond particles. These high temperature annealed diamond particles exhibited enhancements in magnetically induced photoluminescence modulation, enhanced optically driven ¹³C nuclear spin polarization buildup, and extended both NV(-) as well as P1 (neutral substitutional nitrogen) spin relaxation times. Here we present a continued investigation of high temperature annealing, with a focus on the use of extended (>10 hours) high temperature annealing on particulate diamond. Specifically, we explore the impact of such annealing on the photoluminescence and spin properties of NV centers.

Diamond-based color centers have emerged for a variety of applications in quantum communication, quantum photonics, and biological sciences, etc. Optical color center of SiV formed by one silicon atom sited in the middle of two vacancies shows great promise as a single-photon source. Unlike the NV center, which can be improved sufficiently for quantum applications by high-temperature annealing to mobilize only vacancies, SiV center may become unstable in diamond lattice under annealing. Upon annealing to temperatures up to 800 °C, both SiVs and vacancies would become mobile to the surface of diamond. It is unclear during the annealing process whether SiV or vacancy impurity migration dominates and the relative time-scale of the two processes. In this talk, we are going to present our studies to unravel this problem, focusing on the theoretical calculations. An AOM-modulated laser heating and annealing in a diamond anvil cell has been used. The fluorescent intensities of SiV center before and after the annealing were measured using fluorescent spectroscopy. ab initio DFT calculations were used to quantify the dynamics of two impurities. Both experimental and theoretical results suggest that SiV centers can be stabilized associated with the crystalline quality during the production of artificial SiV photonic centers.

Crystalline micro- and nanosized HPHT diamond particles are attracting significant research interest because of the unique combination of mechanical, physical, chemical, and, most importantly, quantum spin properties. The latter properties provide for unmatched opportunities for developing biosensors and quantum information systems. The latter two applications capitalize on quantum physics of optical centers and, primarily, the Nitrogen Vacancy (NV) center. The quantum state of the NV center can be initialized, manipulated with external electromagnetic fields, and then measured with high fidelity due to exceptionally long spin relaxation times even at room temperature. Future progress in this technology calls for fabricating and characterizing ND particles with suitable spin properties. Here we present experimental studies of electronic spin relaxation in microcrystalline HPHT diamond as a function of particle sizes and the processing conditions. Electronic T₁ and T₂ relaxation were measured by pulsed EPR at X- (9.5 GHz, 0.33 T magnetic field), Q-band (34 GHz, 1.2 T magnetic field), and W-band (94 GHz, 3.4 T magnetic field) at 295 and 77 K. The data clearly demonstrate a heterogeneous distribution of electronic relaxation properties. Continuous wave EPR also reveals the presence of spin clusters. We then investigated microcrystalline diamond particles for room temperature dynamic nuclear polarization (DNP) at 300 MHz ¹H NMR frequency by observing static natural abundance ¹³C signal with mm-wave field on and off and compared that with a single crystal HPHT diamond. Significant DNP enhancements were observed for all the samples with >1500-fold enhancement of ¹³C natural abundance NMR signal measured for a single crystal at full incident millimeter wave power. Commercial diamond lapping films such as 3M 666XW incorporating diamond particles were also investigated.

Nitrogen-vacancy (NV) centers have been studied during the last years in different applications, such as materials characterization, spin entanglement, nanoscale magnetometry, and life sciences.
In our work, we use nuclear magnetic resonance (NMR) spectroscopy to an NV sensor, which provides information about a molecular structure and dynamics of a target molecule. When we perform these measurements, data collection takes a long time and is difficult to analyze due to noisy data and magnetic noise. Applying an additional magnetic field gradient allows us to target specific nuclear spins resulting in spectrally separated spin resonance frequencies. Under this condition, two spins at distant locations experience different magnetic fields to increase the spectral resolution. For this, we are using a magnetic force microscope (MFM) to apply magnetic field gradients to a dense nuclear spin sample—immersion oil. The magnetic field gradient will increase the spectral resolution of the external nuclear spins 1H Larmor.
This work paves the way to nano-NMR and other resonance techniques such as nano-MRI.

Fluorescent nanodiamonds (FNDs) are nano diamond particles containing color centers with diameters ranging from ten to a few hundred nanometers. As the fluorescence intensity and zero phonon line (ZLP) position and width of emissions from FNDs can be sensitive to the magnetic field, temperature, and electric field, these non-toxic, highly photo-stable and biocompatible materials have attracted huge research interests and market prospects in many applications such as nano sensors, biomedicine, etc.
However, since most of the application prospects are related to the fluorescence properties of the FNDs, one of the major limitations that hinders the broader application of FNDs is their insufficient brightness compared to conventional organic dyes. Therefore, it is of great importance to explore treatments that can effectively improve the fluorescent intensity of the color centers.
To achieve this goal, researchers have tried various methods, such as oxidation, surface functionalization and integration with polymers. Among these methods, surface oxidation is one of the most effective methods since it is believed to be able to remove the surface non-sp³ structures that detrimentally affect fluorescence performance. Among the oxidation treatment methods, it has been reported that molten salt oxidation produces superior enhancement of fluorescence intensity compared to other surface oxidation methods. The origin of the enhancement has been attributed to the resultant “rounder” particle shape and removal of smaller sized particles.
Here, we have conducted a systematic study of FNDs of equivalent nominal size but with two different surface oxidation treatments: air oxidation at 450 degrees Celsius for 1 hour and 500 degrees Celsius KNO₃ molten salt treatment for 1 hour, respectively. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) with cathodoluminescence (CL) were used to measure the particle size and shape distribution, as well as the emission wavelength and intensity of the FNDs. Statistically representative particle size and shape distributions were analyzed using a machine learning algorithm that was developed in-house.
Our analysis shows that there are only small differences in particle size and shape resulting from the oxidation treatments. Thus, enhancement of fluorescence intensity cannot be attributed to the change in particle morphology. However, we have found that the surfaces of molten salt treated FNDs have a 1-2 nm disordered layer. This disordered layer was not observed in the air oxidation treated FNDs. We attribute the disordered structure on the FND surface to the strong oxidation of the molten salt.
The effect of the disordered surface layer to the fluorescence intensity was further investigated by using oxygen plasma to remove the surface disordered layer of the molten salt treated ed FNDs. The fluorescence intensity of FNDs before and after the oxygen plasma treatment were then compared and cross-analyzed.

COVID-19 highlights the enormous human and economic consequences of an emerging infectious disease. In this invited talk, I will discuss some of the recent breakthroughs by the i-sense EPSRC IRC programme in Agile Early Warning Sensing Systems for Infectious Diseases and Antimicrobial Resistance (www.i-sense.org.uk). We are a large UK-led interdisciplinary research consortium and aim to harness the power of advanced nanosensors, deep learning, genomics and data science to track, test and treat infections much earlier than ever before. Recent research highlights span from advanced materials to detect viruses¹, antimicrobial resistance² and deep learning to support field-based tests in low and middle income settings.³ We also led a recent review of digital technologies in the global public health response to COVID-19.⁴
Herein, I will focus on our work on spin-enhanced nanodiamond biosensing for ultra-sensitive virus detection.¹ The quantum spin properties of nitrogen-vacancy defects in diamond enable diverse applications in quantum computing and communications. However, fluorescent nanodiamonds also have attractive properties for in vitro biosensing, including brightness, low cost and selective manipulation of their emission. Nanoparticle-based biosensors are essential for the early detection of disease, but they often lack the required sensitivity. We are investigating fluorescent nanodiamonds as an ultrasensitive label for in vitro diagnostics, using a microwave field to modulate emission intensity and frequency-domain analysis to separate the signal from background autofluorescence, which typically limits sensitivity. Focusing on the widely used, low-cost lateral flow format as an exemplar, we achieve a detection limit of 8.2 × 10⁻¹⁹ molar for a biotin–avidin model, 10⁵ times more sensitive than that obtained using gold nanoparticles. Single-copy detection of HIV-1 RNA can be achieved with the addition of a 10-minute isothermal amplification step, and is further demonstrated using a clinical plasma sample with an extraction step. This ultrasensitive quantum diagnostics platform is applicable to numerous diagnostic test formats and diseases, and has the potential to transform early diagnosis of disease for the benefit of patients and populations.
References
1. 'Spin-enhanced nanodiamond biosensing for ultra-sensitive diagnostics' Miller, Bezinge, Gliddon, Huang, Dold, Gray, Heaney, Dobson, Nastouli, Morton & McKendry Nature 587, 588 (2020).
2. 'Cantilever sensors for rapid optical antimicrobial sensitivity testing' Bennett, Pyne, McKendry ACS Sensors 5, 3133 (2020).
3. 'Deep learning of HIV field-based rapid tests' Turbe, Herbst, Mngomezulu, Meshkinfamfard, Dlamini, Mhlongo, Smit, Cherepanova, Shimada, Budd, Arsenov, Gray, Pillay, Herbst, Shahmanesh & McKendry Nature Medicine 27, 1165 (2021).
4. 'Digital technologies in the public health response to COVID-19' Budd, Miller, Manning, Lampos, Zhuang, Edelstein, Rees, Emery, Stevens, Keegan, Short, Pillay, Manley, Cox, Heymann, Johnson Nature Medicine 26, 1183 (2020).
Websites
i-sense EPSRC IRC in Agile Early Warning Sensing Systems for Infectious Diseases and AMR: www.i-sense.org.uk
McKendry group website: https://themckendrylab.com/
McKendry UCL website: https://www.london-nano.com/our-people/our-people-bios/rachel-mckendry

A sensitive and specific approach for visualization of lymph nodes with or without tumor cell metastasis using ultrabright 200-nm fluorescent nanodiamonds (FNDs) equipped with a designed targeting surface architecture will be presented. The FNDs with a narrow size distribution were isolated by differential centrifugation, colloidally stabilized with alkyne-functionalized poly(glycerol) and modified with a polyvalent array of mannose. In vitro experiments demonstrated an outstanding increase of the particle internalization by the mannose receptor CD206 (MR) and no significant in vitro toxicity. MR involvement was confirmed by blocking ligand binding with mannan and a 15.2 mAb (anti-MR) in J774A.1 mouse macrophage tumor cells. In vivo mouse experiments confirmed increased retention of FND-p-Man in sentinel lymph nodes of both healthy and tumor-bearing animals. These results suggest that FND-p-Man has a potential as a tracer for lymph node visualization in locoregional cancer diagnostics and as a tool for endoscopic/robot-guided surgery.

By assembling 140 nm-sized fluorescent nanodiamonds (FNDs) in a thin-film on (3-aminopropyl) triethoxysilane functionalized glass surface we prepare magnetically-sensitive FND-fiber probes for endoscopy. The obtained FND layers show good uniformity over large surfaces and are characterized using confocal, fluorescence and atomic force microscopes. Further, FNDs are assembled on single large-core multimode optical fibers (LCF) and imaging fiber bundles (IFB) end face to detect optically detectable magnetic resonance (ODMR) signals. The ODMR signals are recorded through the fiber’s far end in magnetic fields between 0 to 2.5 mT. A multi-channel sensor is demonstrated with the capability of parallel-in-time mapping and instantaneous readout from individual pixel and enabling magnetic mapping at high spatial resolution. Results of this study are regarded as promising candidates during early stage detection in bio-diagnostic applications.

Monitoring multiple modalities simultaneously within a cell remains a technical challenge. Fluorescent nanodiamonds (FNDs) with negatively-charged nitrogen-vacancy (NV) centers, are versatile sensors that can be used to measure different modalities including magnetic field, temperature and quantum nuclear magnetic resonance. [1] Unlike dye based thermometry systems, FNDs have consistency in measurements across environmental factors such as pH, ion concentration and refractive index. NV centers have high optical stability and do not undergo photo-bleaching. We have previously shown FNDs to have both cellular uptake and low cytotoxicity making them a suitable biocompatible sensor for invitro measurements. [2]

Building on our previous results, we now propose using FNDs to simultaneously measure temperature and viscosity within a living cell. Nano-thermometry is achieved by measuring the frequency shift of optically detected magnetic resonance (ODMR) of the NV- center. Local temperature can be measured with high spatial resolution within a single cell and FNDs can be functionalised to target specific regions in a cell, such as the mitochondria, facilitating in situ probing of biological processes. Simultaneously, viscosity measurements are achieved by tracking the movement of the FND inside the cell.

Currently, the inhomogeneous temperature distribution within a single cell remains controversial. Understanding the relationship between temperature, viscosity and the inner workings of a cell would provide insight into many biological processes, including, heat exchange among different organelles. We present our latest data on nanoscale sensing of temperature and viscosity in living systems.

References:
Nanoscale NMR Spectroscopy Using Nanodiamond Quantum Sensors. Physical Review Applied 13, 044004 (2020);
Graphitic and oxidised high pressure high temperature (HPHT) nanodiamonds induce differential biological responses in breast cancer cell lines. Nanoscale 10, 12169 (2018).

Free radicals play a major role in sperm development, including maturation and fertilisation, but they are also linked to infertility. Since they are short lived and reactive, they are challenging to detect with state of the art methodologies. Thus, many details surrounding their role remain unknown. One unknown factor is the source of radicals that play a role in the sperm maturation process. Two alternative sources have been postulated: First, the NADPH-oxidase system embedded in the plasma membrane (NOX5) and second, the NADH-dependent oxidoreductase of mitochondria. Due to a lack of localised measurements, the relative contribution of each source for capacitation remains unknown.
To answer this question, we use a new technique called diamond magnetometry which allows nanoscale MRI to perform localised free radical detection. With this new tool, we were able to quantify radical formation in the acrosome of sperm heads. This allowed us to quantify radical formation locally in real time during capacitation. We further investigated how different inhibitors or triggers alter the radical generation. We were able to identify NOX5 as the prominent source of radical generation in capacitation while the NADH-dependent oxidoreductase of mitochondria seems to play a smaller role.

Nanodiamonds (NDs) are carbon-based nanomaterials that have attracted significant attention over the past decade. NDs provide a unique range of chemical, physical, and biological properties which have driven their application in the fields of drug delivery, tissue engineering, bioimaging and quantum biosensing¹. NDs hosting fluorescence color centres, referred to as FNDs, provide photostable emission, high quantum efficiency and often long fluorescent lifetimes when compared to other organic fluorophores used for cellular imaging. Several color centres are being explored as promising candidates in bioimaging including the nitrogen-vacancy (NV), silicon-vacancy (SiV) and germanium-vacancy (GeV) centres. Recent studies exploiting the quantum properties of the NV centre in FNDs have demonstrated the detection of magnetic^2,3, electric⁴, and temperature fields⁵, as well as pH⁶, redox⁷ and radical species^8-9. These quantum sensors therefore open up new and exciting opportunities to monitor biological activity at the nanoscale.
In this work, I will outline our efforts in applying FND probes to a range of biological problems. I will describe how these materials can be used to enhance the detection limits of biological assays and be applied to probe the intracellular temperature of living cells⁵. I will discuss our recent work exploiting 2D NV imaging arrays for magnetic microscopy. In particular, I will show how these magnetic imaging techniques can be used to non-invasively map the magnetic properties of iron-oxide complexes in biological systems at the sub-cellular scale^10-11. I will also discuss the future possibilities of these technologies and how they might be applied to address significant and outstanding questions in biology.
References:
1. Barzegar Amiri Olia, et al., Advances in the Surface Functionalization of Nanodiamonds for Biological Applications: A Review. ACS Applied Nano Materials 2021, 4 (10), 9985-10005
2. Kaufmann, S.et al., Detection of atomic spin labels in a lipid bilayer using a single-spin nanodiamond probe. PNAS 2013, 110, 10894--10898.
3. Shi, F. et al., Single-protein spin resonance spectroscopy under ambient conditions. Science 2015, 347 (6226), 1135-1138.
4. Karaveli, S.et al., Modulation of nitrogen vacancy charge state and fluorescence in nanodiamonds using electrochemical potential. PNAS 2016, 113 (15), 3938-3943.
5. Simpson, D. A.et al, Non-Neurotoxic Nanodiamond Probes for Intraneuronal Temperature Mapping. ACS Nano 2017, 11 (12), 12077-12086.
6. Fujisaku, T.et al., pH Nanosensor Using Electronic Spins in Diamond. ACS Nano 2019, 13 (10), 11726-11732.
7. Rendler, T. et al., Optical imaging of localized chemical events using programmable diamond quantum nanosensors. Nat. Commun. 2017, 8, 14701.
8. Barton, J. et al., Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds. ACS Nano 2020.
9. Nie, L et al., Quantum monitoring of cellular metabolic activities in single mitochondria. Science advances 2021, 7 (21), eabf0573.
10. McCoey, et al., Quantum Magnetic Imaging of Iron Biomineralization in Teeth of the Chiton Acanthopleura hirtosa. Small Methods 2020, 4 (3), 2070010
de Gille, et al., Quantum magnetic imaging of iron organelles within the pigeon cochlea, PNAS, 2021 in press.

Naturally occurring paramagnetic species, such as free radicals and metalloproteins, play an essential role in a multitude of critical physiological processes including metabolism, cell signaling and the immune response. These endogenous species can act as reporters of biological function and dysfunction. Synthetic paramagnetic probes also have an important role in biological sensing when targeted to specific sites enabling the study of functional information such as tissue oxygenation and redox status in living systems. There is also a need to develop methods to map the uptake of paramagnetic contrast agents used in Magnetic Resonance Imaging (MRI) at a cellular level.
The work presented herein describes sensing methods that exploits the spin dependent emission of photoluminescence (PL) from an ensemble of Nitrogen Vacancy (NV) centers in diamond for rapid, non-destructive detection of paramagnetic species in biological systems. Sensing protocols based on the NV centre charge state switching and magnetic modulation of PL is also assessed providing a simple means to probe biological systems without the application of microwaves. Samples studied include paramagnetic salts in solution, liposomes and mamalian cells. Dynamic tracking of biochemical reactions is demonstrated alongside mapping of the cellular uptake of paramagnetic MRI agents including Gadobutrol, Gadolinium(III) texaphyrin and Manganese(II) texaphyrinby. Overall, this work introduces new protocols for quantum sensing of paramagnetic species using NVs in nanodiamonds for biomedical applications.

Paramagnetic species such as free radicals and transition metal ions play a major role across many aspects of biology. Misregulation of paramagnetic free radicals, for example, has been implicated in a number of diseases (e.g., cardiovascular disease, Alzheimer's disease, cancer, among others). The ability to spatially resolve cellular redox mediators could help draw relationships in disease pathogenesis through a detailed understanding of the location and concentrations of intracellular redox mediators. As the fluorescence of Nitrogen-Vacancy (NV) centers in nanodiamond is sensitive to the NV’s magnetic environment, spin state can be read optically. By measuring fluorescence changes induced by the particle’s environments with respect to laboratory generated static fields, the generated contrast can report on the local paramagnetic environment. Though sensitive paramagnetic responsivity has already been shown via T1 relaxation measurements, by reading this contrast instead we attempt to simply the method for straightforward implementation using conventional microscopy. In the context radical sensing, developments are presented on improving and implementing the ability of NV color centers in nanodiamond to optically sense paramagnetic analytes through magnetically-induced fluorescence contrast.

Nanodiamonds containing the nitrogen-vacancy (NV) colour centre represent an emerging class of materials suited to a range of sensing and imaging applications. Their photostability, surface functionality and range of particle sizes are particularly useful for biological sensing¹. However, to date, the majority of magnetic², temperature, pH⁴, and free radical⁵ sensor demonstrations have been performed using single nanodiamonds. Such approaches are generally time-consuming and limit measurement statistics. In this work, we develop a measurement platform that can report the spin-lattice relaxation time (T₁) for an ensemble of NV-containing nanodiamonds in solution. We have applied this new sensing modality to detect concentrations of biologically relevant metal ions and metalloproteins, as well as establishing the effect of pH on nanodiamonds. This sensing modality is advantageous because it provides ensemble averaging which enables low-noise measurements of high contrast, fast throughput, and high reproducibility.
References:
1. Miller, B. S. et al. Spin-enhanced nanodiamond biosensing for ultrasensitive diagnostics. Nature 587, 588–593 (2020).
2. Kaufmanna, S. et al. Detection of atomic spin labels in a lipid bilayer using a single-spin nanodiamond probe. Proc. Natl. Acad. Sci. U. S. A. 110, 10894–10898 (2013).
3. Simpson, D. A. et al. Non-Neurotoxic Nanodiamond Probes for Intraneuronal Temperature Mapping. ACS Nano 11, 12077–12086 (2017).
4. Fujisaku, T. et al. PH Nanosensor Using Electronic Spins in Diamond. ACS Nano 13, 11726–11732 (2019).
5. Barton, J. et al. Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds. ACS Nano 14, 12938–12950 (2020).

Conductive diamond films emerged twenty-five years ago as an advantageous electrode material for longer-term electrochemical sensing in variety of chemical arenas including in neurochemical detection, with promise of higher chemical sensitivities and less fouling and interferences. More recently reported, nanodiamond (ND) particle sensors, based on modulation of their lattice defect centers, represent a new direction in sensing, while maintaining many inherent advantages of the diamond material. In this work, red fluorescent, carboxylated ND particles with negatively charged nitrogen vacancy (NV⁻) centers are investigated for quantitative detection of dopamine, caffeine and ascorbic acid, with initial comparison of selectivity with electrochemical measurements of these species with diamond electrodes. These molecules are not fluorescent but modulate the ND fluorescence at 685 nm when mixed in a neutral phosphate buffer media. Initial mixing of ND with 25 nM dopamine or caffeine quenched the fluorescence by 10.5% and 7% respectively, with additional quenching of 18.5 and 10.9% respectively for a concentration increase of 75 nM. The quenching was linearly dependent on concentration in the nanomolar range, and was higher for dopamine than caffeine. Ascorbic acid (AA) enhanced the fluorescence by 0.51% when mixing 1 nM AA with ND; its nanomolar sensitivity was less (2.8 % enhancement for a 100 nM change) than for the other species. For micromolar concentrations, the sensitivities for all species was lower.
Fluorescence selectivity for caffeine-dopamine and dopamine-ascorbic acid mixtures were examined and the level of interference was expressed as percentage changes in quenching or enhancement. For caffeine-dopamine mixtures, the interference was less than 1% increase in quenching in the nanomolar or micromolar ranges. For dopamine-ascorbic acid mixtures, the interference was a nominal 3% increase in enhancement in the nanomolar range, and less than 0.5% in the micromolar range. For initial comparison, electrochemical selectivity for dopamine-ascorbic acid mixtures was compared using a carboxyphenyl-modified diamond electrode; dopamine showed higher sensitivity and the AA current was significantly reduced. Caffeine detection was inherently selective since its oxidation potential is readily distinguishable from the potentials for DA and AA. These initial studies demonstrate that for similar surface chemistries, the fluorescence modulation of ND may provide a new sensor modality for comparable detection of important bioanalytes, and may represent an appealing complimentary method to electrochemical detection due to its inherent, high sensitivity, simplicity, speed and low cost.

The room-temperate spin properties of nitrogen-vacancy centres in fluorescent nanodiamond particles make them promising candidates for biosensing. Along with their high brightness, stability and low-cost, the selective manipulation of their fluorescence emission allows separation of their signal from background autofluorescence, which typically limits sensitivity.
There is an urgent need for low-cost, rapid biosensors for early detection of diseases. For example, there are 38 million people living with HIV worldwide, of whom 7.1 million are unaware of their HIV status¹. Lateral flow tests meet many of the REASSURED diagnostic criteria², allowing multi-step assays with little user input. However, the most commonly used gold nanoparticle-based lateral flow tests often lack the required sensitivity for accurate early detection.
We applied fluorescent nanodiamonds containing negative nitrogen-vacancy centres as labels on lateral flow³ to improve diagnostic analytical sensitivity. Nanodiamonds bind to the test line in the presence of the target analyte, after which we used fluorescence imaging to read results. To enhance signal-to-background ratio, and therefore sensitivity, we applied a continuous-wave microwave-frequency electromagnetic field to manipulate nanodiamond emission during imaging. This drives the electron spin population to the m_s=±1 state, reducing the photoluminescent intensity by increasing the probability of decay into a metastable ‘dark’ state. Amplitude-modulating this microwave field, and therefore the modulating fluorescence intensity at a fixed frequency, allows the use of frequency-domain analysis (computational lock-in) to separate the nanodiamond signal from the non-modulated background autofluorescence, improving sensitivity.
This gave a detection limit on lateral flow of 820 zM with an idealised biotin-avidin model, just 27 particles in a 55 µL sample: an improvement of 10⁵-fold over gold nanoparticles. This includes a 100-fold improvement using microwave modulation over conventional fluorescence imaging. Extending to an amplicon detection assay gave a 3.7 fM detection limit, 7,500-fold lower than gold nanoparticles. Applying this assay to the detection of HIV RNA led to single-copy detection with the addition of a short 10-minute isothermal amplification step.
Nanodiamonds are applicable to numerous diagnostic formats and targets, with the potential to dramatically improve sensitivity of low-cost diagnostics.
(1) UNAIDS. Global HIV & AIDS statistics — 2020 fact sheet https://www.unaids.org/en/resources/fact-sheet (accessed Jan 7, 2021).
(2) Land, K. J. et al. REASSURED Diagnostics to Inform Disease Control Strategies, Strengthen Health Systems and Improve Patient Outcomes. Nat. Microbiol. 2019, 4 (1), 46–54. https://doi.org/10.1038/s41564-018-0295-3.
(3) Miller, B. S. et al. Spin-Enhanced Nanodiamond Biosensing for Ultrasensitive Diagnostics. Nature 2020, 587 (7835), 588–593. https://doi.org/10.1038/s41586-020-2917-1.

Carbon nanomaterials synthesized through detonation, including nanodiamonds, are known to form aggregates requiring postprocessing to separate. We are using advanced, synchrotron-based time-resolved x-ray scattering to observe these nanomaterials form during the actual detonation events. The nascent morphologies depend on explosive used and what phase carbon products reach under differing pressure and temperature conditions. In all cases producing nanodiamond, aggregation into low fractal dimension structures is apparent as early as 100 ns, suggesting that aggregation occurs on timescales comparable to particle formation. A counterexample is the case of a high-explosive that reaches pressures and temperatures deeply into the carbon liquid phase and that ultimately produces novel carbon nano-onion structures. In this case, no hierarchical scattering was observed for at least 10 μs behind the detonation front. The novel and varied nanomaterials produced by carbon-rich explosives, and what parameters may be tuned during detonation to affect detonation nanodiamond synthesis will be discussed. Additionally, we are now beginning to determine the feasibility of time-resolved core-level x-ray Raman, or variants thereof, implemented at next-generation x-ray light sources, to interrogate nitrogen, carbon, and/or oxygen chemical evolution at nanosecond to microsecond timescales during detonation.

The first artificial nanodiamonds were produced in the 1960s by USSR scientists using a detonation process. In the late 1990s, there was a growing interest in this material since detonation nanodiamonds (DNDs) became available on a large scale. NDs inherit most of their properties of the bulk, such as strong hardness, high thermal conductivity and electrical resistivity, as well as interesting optical properties and fluorescence. NDs are also biocompatible, leading to a large field of possibilities for biomedical applications. The surface of NDs is also highly reactive, thus allowing drug-delivery applications. Nowadays, NDs have high potential in neutronics for slow neutron reflectors [1], magnetic resonance imaging, tribology and lubrification, nanofluids, and in biomedical (cancer treatment, drug delivery, etc.) [2,3].
However, detonation and purification processes of NDs produce a non-negligible amount of impurities. The sp² carbon layer at their surface, the presence of surface functional groups (-OH, -COOH, -CO, etc.) and metallic impurities are especially unfavorable for neutron applications because of their high neutron absorption [1]. Metallic impurities, which can act as “Trojan horses” are undesirable in biomedical applications since they cause more harms than goods. A universal method producing pure NDs does not exist so far; therefore all the DNDs in the industry are different, with a variable amount of impurities [4]. Thus, there is a real need to understand the composition of DNDs in order to obtain high purity DNDs. Adding the fact that the metallic impurities can be present at a content of 1-2 wt.% in the commercial DNDs, without knowing their specific localization (on the surface or within ND clusters), most of the characterization techniques reach their limits of detection (LOD) making impurity identification complicated. The use of sensitive but standard techniques (contrary to Neutron or Prompt-Gamma Activation Analysis and high-resolution ICP-MS) is of urgent need to fully exploit commercial DNDs for the promising applications [1,5].
In this paper, we propose to apply highly selective methods to efficiently purify DNDs. Halogen chemistry has the potential to fully match the requirements of the development of a scalable approach to produce high-purity DNDs. One-pot straightforward gaseous thermal treatments based on chlorine and fluorine gases are shown to selectively remove the metallic impurities and the surface functional groups, respectively with high removal yield. Moreover, with the purpose of filling the gap of understanding of DNDs, we propose an unprecedented method to determine the nature of their metallic impurity inclusions. Total oxidation of DNDs is simply carried out leading to consumption of the carbon species and revealing the remaining impurities in an oxidized state (Me-O) in a highly concentrated state. In order to characterize these impurities in NDs and Me-O, standard techniques have been used, such as Thermogravimetric Analysis, Powder X-Ray Diffraction, X-ray photoelectron spectrometry, Mössbauer, infrared and Raman spectroscopies, as well as Scanning and Transmission Electron Microscopy analyses. The approach proposed here could become a universal process to concentrate the metallic impurities contained in any kind of carbon nanomaterial sample, offering that way a reliable tool overcoming the LOD of all standard characterization techniques for detection and quantification of metal-based impurities.
References:
1 V. Nesvizhevsky, U. Köster, M. Dubois, N. Batisse, L. Frezet, A. Bosak, L. Gines and O. Williams, Carbon, 2018, 130, 799–805.
2 V. N. Mochalin, O. Shenderova, D. Ho and Y. Gogotsi, Nature Nanotech, 2012, 7, 11–23.
3 K. Turcheniuk and V. N. Mochalin, Nanotechnology, 2017, 28, 252001.
4 V. Y. Dolmatov, Russ. Chem. Rev., 2001, 70, 607–626.
5 P. N. Nesterenko, D. Mitev and B. Paull, in Nanodiamonds, ed. J.-C. Arnault, Elsevier, 2017, pp. 109–130.

Contradicting the current opinion that 3-5nm detonation nanodiamonds (DNDs) are monodispersed after their purification, more recent work indicates that even with further surface modifications, DNDs form lacey networks in water in the size range of approximately 100nm. This has significant implications for the use of DNDs in biomedicine, where control of the aggregation behavior is critical to their performance. However, ensuring reliable colloidal stability of DNDs in in-vitro environments is not trivial. This is because any type of nanoparticle surfaces rapidly adsorb macromolecules such as proteins and lipids when being introduced to biological media (e.g. blood or cell culture media containing serum). Additionally, the dynamic environment of high salt concentrations, presence of electrolytes and shifting pH, can result in colloidal destabilization, nanoparticle aggregation, loss of stabilizing ligands on the nanoparticles’ surface and nanoparticle dissolution. Hence, neglecting the characterization of DNDs in biologically relevant buffers may lead to inconsistencies and irreproducibility in data.
In this work we present a systematic study on DNDs with different surface functionalization (-COOH, -OH, -H, -PG) dispersed in buffer with varying pH and saline concentrations using high performance characterization techniques such as small angle X-ray scattering (SAXS) and a new approach of combining machine learning (ML) with cryo-transmission electron microcopy (cryo-TEM) for a quantitative image analysis to get an accurate insight on the performance of DNDs. Our results indicate that depending on the surface functionalization the colloidal behavior and aggregation formation significantly changes. With the help of ML and cryo-TEM we are able to generate a data bank of different scenarios of DNDs behavior in biologically relevant environments, which is a significant aid in creating safer and more efficient DNDs for biomedical applications.

At least 1 billion people lack access to safe water due to rapid population growth, urbanization, industrialisation and the climate emergency. One of the biggest challenges to water purification is the removal of harmful nanoscale contaminants such as viruses and industrial contaminants such as dyes and pharmaceutical by-products. Of the existing filtration platforms, only nanofiltration or reverse osmosis can achieve high retention levels of such nanoscale pathogens. These systems are expensive and complex, being mostly limited to centralised water treatment systems. This has led to the development of adsorptive depth filtration (ADF) where contaminants are targeted by van der Waals / electrostatics forces, hydrophobic interactions etc driving contaminant adsorption to the membrane surface. A key advantage of such a technology is that retention is not achieved through size exclusion, allowing much higher flow rates and smaller pressure differentials.
In this work¹, quartz filters are modified with hydrogenated diamond nanoparticles, reversing the zeta potential of the membranes from negative to positive across a wide pH range. Untreated quartz filters demonstrate log0.2 (35%) retention of viruses (MS2 bacteriophage) whereas the diamond modified ones exhibit at least log6.2 (>99.9999%) reduction from feed waters. This is due to the overwhelming majority of viruses exhibiting a negative zeta potential in water and thus being attracted to the positively charged diamond modified membrane. The modified membrane was also tested with far smaller contaminants such as acid black 2 dye and demonstrated >90% higher retention over the unmodified filter. Finally, the diamond modified filter was compared to the incumbent alumina-based technology where it demonstrated a consistently higher positive zeta potential over a larger pH range. Thus, diamond modified filters offer higher zeta potentials vs pH and thus higher virus retention over current ADF technologies.
¹ H.A. Bland, ACS Appl. Nano Mater. 4, 3252 (2021).

Using nanoparticles has gained attention due to their small size and high surface to volume ratio, but there are many concerns about their harmfulness for the living organisms. According to the studies available in the literature, the NDs are theleast toxic and the most biocompatible carbon nanomaterials and therefore can be considered as a suitable nanocarriers for targeted drug delivery, improving therapeutic value of various drugs [1]. Nanodiamonds (ND) have emerged since about a decade ago as a key platform for many developments in nanoscience and nanotechnology due to their outstanding mechanical performance, biocompatibility and unique properties. Their large accessible surface allows enlarged loading of drugs, while their surface chemistry could be easily tuned to increase permeability into targeted tissue and enhance the selectivity of drug actions while reducing the adverse effects of their use [2]. NDs also interact with plasma proteins in the blood and cellular enzymes upon crossing the target cell membrane. As a result, the nanoformulation is rapidly excreted from the bloodstream by the kidneys, ending up in an incomplete delivery of the drug release at the targeted sites. By using different techniques of drug coating over the nanoparticle, the circulation time of a drugs in blood, their permeability pathways into the target cells, and controlled release inside can be controlled by changing the type of coating, which greatly affects the overall properties of the nanocarrier. Recently, NDs were reported to affect endothelial permeability to deliver anticancer drugs [3, 4]. Another report included delivery of the quaternary oxime antidotes to the cell lines simulating BBB in order to manage acute poisoning with organophosphorus toxic agents [5].
This study focuses on the basic concept underlying the approach for tuning behavior of NPs by covalent bunding on the ND surface vs non-covalently bound agents - (i) pyridinium oximes as scavengers or antidotes-cholinesterase reactivators; (ii) oxazolopyrimidines as promising anticancer agents [6], whereby the fundamental characteristics such as transportation into (i) BBB simulating (MDCK and HUVEC grown in astrocyte medium) and (ii) oncogenic cells (HeLa), localization inside, and anti-cancer activity (cell viability) were studied. The properties of obtained nanocarriers (surface drug density, aggregation, surface modification) were investigated by FTIR, XRD, DLS, and TEM. Shedding light on the way of cell permeability may give a clue for a surface coating to achieve targeted drug delivery. The advantages of different coating techniques are being discussed.
Aknowledgement. DB and YK acknowledges NATO SPS MYP No.G5565 (DEFIR) for support of this study.
References:
[1] K. Turcheniuk, V. N. Mochalin Nanotechnology, 2017, 28, 27.
[2] N. Bondon et al. Journal of Materials Chemistry B 2020, 8 (48), 10878-10896.
[3] M. I. Setyawati, V. N. Mochalin, and D. T Leong. ACS Nano, 2016, 10, 1170.
[4] H. Li, D. Zeng, Z. Wang, L. Fang, F. LI, Z. Wang. Nanomedicine 2018, 13, 981
[5] (a)Y. Karpichev et al. 2020 Virtual MRS Spring Meeting & Exhibit, Boston, 2020. Material Research Society, S.NM01.10.06. (b) D. Bondar et al, submitted.
[6] Ye. Velihina, Th. Scattolin, D. Bondar, S. Pil'o, N. Obernikhina, O. Kachkovskyi, I. Semenyuta, I. Caligiuri, F. Rizzolio, V. Brovarets, Y. Karpichev, S.P. Nolan. Helvetica Chimica Acta, 2020, 103 (12), #e2000169

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and it is extremely aggressive and lethal, which commonly shows poor prognosis. Small interfering RNA (siRNA) can cause specific gene silencing. Considering that HCC is a highly heterogeneous disease which diverse oncogenes are involved in, siRNA-based gene therapy could be a potential strategy for HCC therapy. However, naked, unmodified siRNA is relatively unstable under physiological conditions and has difficulty crossing the cell membrane. Nanodiamond (ND) is carbon nanoparticle that can be used as a delivery platform. It’s highly biocompatible and well tolerated in various biological systems. Positively charged ND can bind to siRNA through electrostatic interactions. The ND-siRNA complex renders efficient cellular uptake and endosomal escape that protects siRNA from degradation.
Poor penetration into solid tumors is another critical issue that limits siRNA application. Herein, we demonstrate that delivered by ND, siRNA is able to penetrate inside the tumor spheroids. The enhanced penetration capacity making ND an ideal vehicle to deliver siRNA. We further investigate the gene knockdown efficiency of siRNA targeting SALL4 delivered by ND. ND-siSALL4 can significantly knock down the SALL4 expression in tumor spheroids, which results in decreased proliferation in spheroids. Our study demonstrates the potential for ND as a promising gene delivery platform in tumor spheroids.

Titanium alloys are widely used in commercial dental implants (DI). However, Ti-alloys can suffer electrochemical corrosion from oral fluids, releasing TiO₂ particles from the oxidized Ti surface, as confirmed by published articles by our and other groups worldwide, causing tissue inflammation and implant failure in undesirable short time, requiring implant change (~ 15% of DI, inserted in humans in the world, fail in the first 4-5 years), resulting in patients’ health discomfort and extra cost.
A novel ultrananocrystalline diamond (UNCD^TM) coating developed and patented by Auciello and colleagues exhibit outstanding mechanical / biocompatible properties and strong resistance to chemical attack by body fluids, as previously shown for UNCD^TM-coated Si microchip implanted in human eye to restore partial vison to people blinded by genetically-induced retina’s photoreceptors degeneration. This presentation describes R&D performed to develop the technology to produce UNCD^TM-coated commercial Ti alloys-based DIs, using an industrial MPCVD system enabling coating of 100s DI in a single low-cost fabrication process. UNCD coatings are produced by flowing Ar/CH₄ gas mixture in air evacuated chamber, creating a plasma producing UNCD^TM film growth. Several dental implants (DI) were coated, on a holder capable to hold up to 300 DIs (~ 8 mm log, 2-3 mm diameter) vertically distributed in circular patterns. A uniform plasma was produced around all implants, coating them in a single process, with extremely uniform UNCD films (~ 0.2 - 0.3 µm thick), as shown by Raman, SEM and HRTEM analysis. Chemical analysis showed that UNCD^TM-coated DI are not corroded, as Ti-DI are. Histological studies of UNCD-coated Ti-alloy DI, tested/analyzed/ assessed in an in vivo animal model, performed in a collaboration between UTD and Drs. Olmedo and Tasat in Argentina, showed outstanding biocompatibility of UNCD coating and superior osseointegration of the UNCD-coated Ti-alloy DI, in the animal bone, due to superior high density growth of bonce cells on the surface of UNCD coating, and total corrosion resistance, in contrast to current commercial Ti-alloy based dental implants, which are corroded and induce lower density of bone cells growth. In addition, UNCD-coated Ti and Ti-6Al-4V alloys exposed to artificial saliva (pH 6.5) showed no corrosion. UNCD-coated commercial Ti-6Al-4V DI have been implanted in 20 humans, in clinical trials since 2018, conducted by Dr. Giberto López-Chávez, in the world class Institute Bioingeniería Humana Avanzada in Querétaro-México. Extensive X-ray and biological performance studies have shown that UNCD coated DI provide the new revolutionary DI technology, which is planned for insertion into the world market by 2022-2023.

Detonation nanodiamonds (DNDs) in the size range of 3-5nm have a wide range of possible applications [1]. DNDs are known to form aggregates in solutions in the size range of approximately 50-100nm. [2,3] Understanding the aggregation in solution as well as techniques to disperse them onto substrates are essential [4].
Here, we show a tight binding between DNDs and graphene oxide (GO) sheets in solution. We observe that the DNDs are adsorbed in a chain-like structure onto the GO sheets confirming previous cryo-Transmission electron microscopy (cryo-TEM) measurements that showed the chain-like structure in aqueous solution [5]. Well dispersed DNDs on GO sheets allow stable HRTEM analysis. Further, the dispersed DNDs on GO can be transferred to a solid substrate such as SiO₂. The interaction between GO and DNDs were investigated by manipulating the surface charge of DNDs. To test the robustness of the interaction the GO/DND films as membranes, they were tested for water purification purposes. The stable membrane performance over several hours suggests that DNDs are bonded well with GO and are stably intercalated between the GO sheets.
In summary, we demonstrate that the interaction between DNDs and GO is steady and allows to produce well dispersed DNDs on solid substrates, within 2-D laminar membranes as well as freestanding on TEM grids. Therefore, our results help to understand the interaction between GO and DND and open possible applications with well-dispersed DNDs in various forms.
1. Nanodiamonds, ed. J.-C. Arnault, Elsevier, 2017, pp. 1–24
2. J. Phys. Chem, 3(7):896–901, 2012.
3. J. Mater. Chem., 18:4038–4041, 2008.
4. Nanoscale, 2020, 12, 5363-5367
5. Nanoscale, 2021, 13, 14110-14118

The in-field superconducting transport properties of YBa₂Cu₃O_7-δ (YBCO) film can be significantly improved through the introduction of nanosized defects that may have a beneficial effect on film properties in the conditions generally requested for fusion applications, i.e. low temperatures and high magnetic fields. The incorporation of different metal oxides as secondary phases into YBCO has been extensively investigated in the past. On the contrary, Nanodiamond (ND) introduction in YBCO film (YBCO-ND) has never been reported until our preliminary study on chemical solution deposited YBCO-ND film grown by Metal Organic Decomposition approach and the “ex situ” route using ND as preformed nanoparticle. Our first attempts showed ND potential for the improvement of YBCO transport properties [1]. In fact, ND suspension in YBCO compatible solvent, i.e. propionic acid, was prepared and nanoparticles with uniform size below 10 nm were obtained. Despite the uncertainty and the low amount of nanoparticles concentration, ND suspension was used for YBCO precursor solution preparation and epitaxial films were obtained. An improvement of film morphology and superconducting properties was observed. Therefore, further investigations of ND influence on YBCO nucleation and growth appeared to be necessary.
In the present work, the effect of ND on the YBCO nucleation mechanism has been evaluated in order to elucidate the role of ND in promoting film growth. A detailed study on YBCO-ND films quenched at different temperatures of the crystallization process was carried out. Results showed that the reaction responsible for YBCO nucleation appeared effectively affected by ND. Some hypotheses as well as some possible and positive implications of this study will be provided.
Furthermore, ND functionalization has been explored in order to favor the interaction between nanoparticle and solvent and, consequently, to obtain higher and precise ND concentrations, in addition to a more stable precursor solution. Different routes have been attempted. The oxidation through acidic treatment resulted in dramatically decrease nanoparticle stability and dispersibility in YBCO solvent. Therefore, the route of functionalization by radical chemistry was exploited due to its general high efficiency under mild operative conditions. In particular, the work aimed to set up suitable experimental conditions to selectively hydroxylate ND tertiary C-H bonds by means of dioxirane chemistry. It is worth noticing that, so far, such radical route was experimented only on simpler diamondoids system. The results thus obtained will be discussed.
[1] Pinto et al., Thin Solid Films 2020. Doi.org/10.1016/j.tsf.2019.137696

Acknowledgments
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Atom probe tomography (APT) is a technique that uses the controlled field evaporation of ions from a sample to reconstruct a nanoscale 3D model with near-atomic resolution. This technique has been used to study the atomic nanostructure of many different materials, ranging from biological materials to nanodiamond inclusions in meteorites. To prepare samples for APT, the region of interest must be mounted on a micropost and milled into a sharp point, typically using a focused ion beam (FIB). Usually, this process involves lifting out a bar with a triangular cross section and iteratively welding slices of the liftout onto microposts, and then individually sharpening each section. This is a reliable method for most thin-film and bulk samples, but challenges remain in preparing nanoscale diamond samples for APT analysis. For example, the liftout process requires relatively large trenches to be milled into the substrate, and the sharpening process also removes a significant amount of material. For particularly hard materials, such as diamond, this can be time-consuming, and the higher currents required to mill these hard materials can introduce difficulties with charging, especially in nonconductive materials like diamond. Charging also makes it difficult to mill with the precision required to fabricate APT tips. Here we present recent results using microfabricated diamond pillars with nanoscale radii of curvature and a novel FIB liftout procedure in order to improve the process and allow the simple fabrication of APT tips out of nanoscale diamond materials. In this procedure, a diamond membrane was glued to a sapphire substrate and thinned to 10 μm. Subsequently, many 10 μm pillars were dry-etched from the remaining diamond, forming conical nanoscale pillars roughly 2 μm at the base; this is the same diameter as the flat surface of the microposts used to mount APT samples. These posts can then be individually coated with a thin protective layer of platinum and lifted out by cutting near the base at a 52-degree angle to vertical. These can then be attached to the microposts by welding the gap formed by the angled cut. Following this process, minimal if any additional sharpening of the tips is required, only a light FIB polish to remove excess platinum and make minor shape adjustments. This procedure allows the efficient lift-out of well-shaped nanoscale diamond APT tips without the need to remove large amounts of material in the FIB, eliminating a major bottleneck. Additionally, this method allows the lift out of specific pillars, which may be useful for applications where there is a need to investigate individual pillars with well-defined quantum emitters. This approach also has the benefit of being able to measure entire pillars in applications for which the pillar morphology is important to the material’s properties, for example in the case of microcavities for single photon emission or diamond electrodes for bioelectronics.

A method using an atmospheric pressure plasma system to convert the gas CO into an extended solid is being developed by Rivis Inc. Dendritic deposits of cauliflower structures result from treatment of CO in a dielectric barrier discharge (DBD) system. Deposits that accumulate on the dielectric barrier material and bare metal electrode may be collected for subsequent use. Extended solids are materials that are typically formed at extremely high pressure and temperature using methods that severely limit the amount of material that can be produced. The use of a DBD plasma system is important in that it is a non-equilibrium plasma that allow one to maintain electrode temperatures < 30°C with cooling even at high discharge powers and high frequency operation. This allows one to deposit the temperature sensitive materials for collection. To increase the deposition rate, we are exploring the use of diamond particles as substrates for deposition of the extended solids. The benefits of using a particulate substrate versus a planar substrate include: (i) significantly increased deposition surface area as compared to a planar surface; (ii) ease and convenience for collection and storage of the final product. The coated particles can be easily removed and transferred to a solvent or used as-is. Use of diamond particles is motivated due to their superior inertness as compared to other candidate materials when exposed to the reactive plasma conditions. Even though diamond is known to be stable to even harsh chemical conditions, it is readily functionalized which contributes to good adherence of the carbon sub(oxide) (COx) extended solids. Upon optimization of the plasma parameters (power, frequency, gas composition and flow rate) for the most efficient COx growth, particle size, amount of particles, particle surface composition and particles placement in the reactor are particle-specific parameters for optimization which will be discussed. Particularly, particle size is an important parameter in two regards: (i) in the process of nucleation and growth of COx (compatibility of the feature sizes between deposit/substrate at a microscale) and (ii) resulting substrate area increase for the COx growth. We will report results of the investigation of particle size dependent growth over the size range from 100 nm to 100 um, and the most suitable parameters for the growth of CO-based extended solids on particulate diamond substrates.

High-pressure high-temperature nanoscale diamond (ND) is the most common host of the nitrogen vacancy center (NVC) for magnetometry and electric field sensing applications. Limiting advancements in NVC charge state control and atomic/molecular control of the diamond surface are the limited chemical routes to removing C-O bonds after aerobic oxidation protocols. Bromination of the ND surface is a robust route for chemical activation using SOBr₂. Previous discoveries about the highly labile C-Br bond on the diamond surface revealed that catalysis-free C-N bond formation was possible at 25^oC and is due to the lability of the alkyl-bromide and a long-lived reactive intermediate. Here we expand the available bond formation chemistry using the reactive C-Br intermediate to generate new C-N and C-C bonds with amines and carbenes. Atomic and molecular details of the diamond surface are confirmed with vibrational spectroscopy and synchrotron-based X-ray spectroscopies. The removal of the highly stable C-O bond allows tunablility of the surface dipole moment with carbon-carbon and carbon-heteroatom bonding environments. The modulation of the surface dipole moment change the depletion and accumulation layer properties of the diamond host and was confirmed with work function measurements. These discoveries are applicable to researchers investigating the modulation of NVC (or other colour centers) photophysics and their use as a biolabeling and quantum sensor nanoprobe.

Paramagnetic centers in solids’ subsurface region are being investigated for applications to spintronic-based devices, and magnetic/chemical/biological sensors, with paramagnetic centers tailoring magnetic interactions with electrons or nuclear spins at the solid / environment interface. Key to the applications mentioned above is formation of nitrogen-vacancy (NV) centers, via N atoms in substituted C atoms lattice position, adjacent to a missing C atom (vacancy) in the diamond lattice.
Work to be discussed relates to initial research focused on investigating fundamentals of NV-centers formation in the subsurface region of single crystal diamond (SCD). Experiments were performed in a commercial XPS system with base pressure of 4×10^-8 Pa. XPS spectra recorded after N⁺ ion bombardment of the SCD surface provide direct quantifiable information on the amount of N atoms implanted in the diamond lattice, by measuring the area of the N 1s peak, and direct evaluation of the diamond surface conductivity, via monitoring of the C 1s peak position. The high vacuum XPS system with integrated XPS analysis/ion beam sources enable unique studies described below.
Formation of NV-Centers in the subsurface region (~ 5 nm depth) of SCD was demonstrated by bombarding SCD electronic grade samples (negligible N content) with low energy (250-4000 eV) N₂ ⁺ ions, generated by a small area (5x5 mm) N₂⁺ ion beam, impacting on the diamond surface at ~ 45 degrees with respect to the normal. Prior to N⁺ ion implantation, the SCD surface was cleaned by in situ Ar Gas Clusters Ion bombardment (AGCIB) (2500 atoms/cluster, ionized to +1, delivering Ar⁺ ions impacting on the surface of the SCD with 8 eV of energy each to sputter atoms from the surface only and negligible radiation damage in the subsurface region), for ~15 mins., until impurity elements (mainly O, H, N), from atmosphere exposure, were removed from as received samples’ surface. XPS analyses were performed, following cleaning, until the peak intensities for N and O, as impurities from atmospheric exposure, were “0”. Following the cleaning process, N⁺ ions were implanted with energies in the range 125- 2000 eV, resulting from rupture of bombarding N₂⁺ ions with energies of 250-4000 eV, to investigate the range of N distribution underneath the surface. XPS analysis revealed the appearance of two N peaks, with the peak at 398 eV, appearing when bombarding the SCD surface with 125 eV N⁺ ions, correlating with the shift of the C 1s peak from 284. 3 eV to 285 eV, which indicates that the SCD surface changed from insulator to electrically conductive, due to N atoms inserted in the SCD diamond lattice, replacing C atoms and releasing electrons to the conduction band (surface electrical conductivity was confirmed by four probe and Hall measurements). The samples were annealed in situ in the XPS system to ~500 C for times between 30 minutes to 5-6 hrs. to investigate the effect of annealing time on NV centers formation.
Studies of NV centers were performed, using a confocal microscope, in which spin manipulation is carried out using the microwave field from a thin copper wire across the diamond crystal. Optical pictures of single-color center were obtained using time-correlated photon counting. A microwave sweep was used to determine the NV center magnetic resonance spectrum revealing splitting of the ground triplet in two, as expected, via point-by-point detection of Rabi oscillations.
HRTEM studies revealed diamond lattice changes due to N ions implantation, extending to about 5-7 nm, which correlates with the information provided by the XPS depth profiling of implanted N atoms.
In summary, the research to be discussed shows that NV-centers can be produced at nanometer depth from the SCD surface, with much lower energy N⁺ ions than used until now by most groups. An additional discovery is that low N atoms subsurface implantation induces surface electrical conductivity in SCD.

Nitrogen-vacancy (NV) centers have been studied during the last years in different applications, such as materials characterization, spin entanglement, nanoscale magnetometry, and life sciences.
In our work, we use nuclear magnetic resonance (NMR) spectroscopy to an NV sensor, which provides information about a molecular structure and dynamics of a target molecule. When we perform these measurements, data collection takes a long time and is difficult to analyze due to noisy data and magnetic noise. Applying an additional magnetic field gradient allows us to target specific nuclear spins resulting in spectrally separated spin resonance frequencies. Under this condition, two spins at distant locations experience different magnetic fields to increase the spectral resolution. For this, we are using a magnetic force microscope (MFM) to apply magnetic field gradients to a dense nuclear spin sample—immersion oil. The magnetic field gradient will increase the spectral resolution of the external nuclear spins 1H Larmor.
This work paves the way to nano-NMR and other resonance techniques such as nano-MRI.

Fluorescent nanodiamonds (FNDs) are nano diamond particles containing color centers with diameters ranging from ten to a few hundred nanometers. As the fluorescence intensity and zero phonon line (ZLP) position and width of emissions from FNDs can be sensitive to the magnetic field, temperature, and electric field, these non-toxic, highly photo-stable and biocompatible materials have attracted huge research interests and market prospects in many applications such as nano sensors, biomedicine, etc.
However, since most of the application prospects are related to the fluorescence properties of the FNDs, one of the major limitations that hinders the broader application of FNDs is their insufficient brightness compared to conventional organic dyes. Therefore, it is of great importance to explore treatments that can effectively improve the fluorescent intensity of the color centers.
To achieve this goal, researchers have tried various methods, such as oxidation, surface functionalization and integration with polymers. Among these methods, surface oxidation is one of the most effective methods since it is believed to be able to remove the surface non-sp³ structures that detrimentally affect fluorescence performance. Among the oxidation treatment methods, it has been reported that molten salt oxidation produces superior enhancement of fluorescence intensity compared to other surface oxidation methods. The origin of the enhancement has been attributed to the resultant “rounder” particle shape and removal of smaller sized particles.
Here, we have conducted a systematic study of FNDs of equivalent nominal size but with two different surface oxidation treatments: air oxidation at 450 degrees Celsius for 1 hour and 500 degrees Celsius KNO₃ molten salt treatment for 1 hour, respectively. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) with cathodoluminescence (CL) were used to measure the particle size and shape distribution, as well as the emission wavelength and intensity of the FNDs. Statistically representative particle size and shape distributions were analyzed using a machine learning algorithm that was developed in-house.
Our analysis shows that there are only small differences in particle size and shape resulting from the oxidation treatments. Thus, enhancement of fluorescence intensity cannot be attributed to the change in particle morphology. However, we have found that the surfaces of molten salt treated FNDs have a 1-2 nm disordered layer. This disordered layer was not observed in the air oxidation treated FNDs. We attribute the disordered structure on the FND surface to the strong oxidation of the molten salt.
The effect of the disordered surface layer to the fluorescence intensity was further investigated by using oxygen plasma to remove the surface disordered layer of the molten salt treated ed FNDs. The fluorescence intensity of FNDs before and after the oxygen plasma treatment were then compared and cross-analyzed.

Detonation nanodiamonds (DNDs) in the size range of 3-5nm have a wide range of possible applications [1]. DNDs are known to form aggregates in solutions in the size range of approximately 50-100nm. [2,3] Understanding the aggregation in solution as well as techniques to disperse them onto substrates are essential [4].
Here, we show a tight binding between DNDs and graphene oxide (GO) sheets in solution. We observe that the DNDs are adsorbed in a chain-like structure onto the GO sheets confirming previous cryo-Transmission electron microscopy (cryo-TEM) measurements that showed the chain-like structure in aqueous solution [5]. Well dispersed DNDs on GO sheets allow stable HRTEM analysis. Further, the dispersed DNDs on GO can be transferred to a solid substrate such as SiO₂. The interaction between GO and DNDs were investigated by manipulating the surface charge of DNDs. To test the robustness of the interaction the GO/DND films as membranes, they were tested for water purification purposes. The stable membrane performance over several hours suggests that DNDs are bonded well with GO and are stably intercalated between the GO sheets.
In summary, we demonstrate that the interaction between DNDs and GO is steady and allows to produce well dispersed DNDs on solid substrates, within 2-D laminar membranes as well as freestanding on TEM grids. Therefore, our results help to understand the interaction between GO and DND and open possible applications with well-dispersed DNDs in various forms.
1. Nanodiamonds, ed. J.-C. Arnault, Elsevier, 2017, pp. 1–24
2. J. Phys. Chem, 3(7):896–901, 2012.
3. J. Mater. Chem., 18:4038–4041, 2008.
4. Nanoscale, 2020, 12, 5363-5367
5. Nanoscale, 2021, 13, 14110-14118

Daicel, as a century-old company, has worked on products and services for the medical field over many years. Specifically, we have manufactured several active pharmaceutical ingredients (APIs) and intermediates. In recent years, we launched new products of novel concept such as pre-mixed excipient for orally disintegrating (OD) tablets, as exemplified by “Granfiller-D^TM”, and pyro-drive jet injector “Actranza^TM Lab”.
In the meantime, there have been a lot of publications for biomedical application of nanodiamonds (NDs). Since Daicel have been developing detonation nanodiamond (DND) products, “Dinnovare^TM”, these statements motivate us to pursue our NDs to apply in this field. In the talk, we introduce the following topics as our representative R&D activities related to DNDs.
1. Polyglycerol modified nanodiamonds (DND-PG)
DND-PG have originally been created by Prof. Komatsu in collaboration with Daicel [1]. They are highly dispersible in water of even high ionic concentration and, thereby, promising in various applications. In this context, we have developed manufacturing process of DND-PG for commercial production. As well, we are seeking applications such as nanodrugs for cancer treatment through further precise chemical modification, and exploring unique and prominent dispersive characteristics [2, 3].
2. Fluorescent detonation nanodiamonds (f-DNDs)
Color centers such as nitrogen-vacancy (NV), silicon-vacancy (SiV) and other heteroatom-related centers have been studied by many groups for bio-sensing and imaging. DNDs having color centers are especially desired because of their comparable size to biomolecules, which should be advantageous to trace those molecules in cells. Recently, we successfully synthesized single-digit SiV-DNDs via straightforward detonation process, in which a selected silicon-containing compound was mixed in explosive charge [4]. We are exploring applications of f-DND as well as fabrication of other color centers.
3. Nanometer-scale ordered precise arrangement of DNDs on substrate
We have developed a novel technique to arrange DND particles on a substrate in nanometer-scale [5]. Using the lift-off process combining electron beam lithography and surface functionalization, the static electrical charge of substrate is locally controlled and precise patterning with DND particles by the electrostatic deposition can be achieved. This technique will open the way to nanometer-scale sensors using DNDs.
[1] L. Zhao, T. Takimoto, M. Ito, N. Kitagawa, T. Kimura, and N. Komatsu, Angew. Chem. Int. Ed. 2011, 50, 1388.
[2] M. Nishikawa, H. G. Kang, Y. Zou, H. Takeuchi, N. Matsuno, M. Suzuki, and N. Komatsu, Bull. Chem. Soc. Jpn. 2021, 94, 2302.
[3] T. Yoshikawa, M. Liu, S. L. Y. Chang, I. C. Kuschnerus, Y. Makino, A. Tsurui, T. Mahiko and M. Nishikawa, “Steric interaction of polyglycerol-functionalized detonation nanodiamonds”, in press.
[4] Y. Makino, T. Mahiko, M. Liu, A. Tsurui, T. Yoshikawa, S. Nagamachi, S. Tanaka, K. Hokamoto, M. Ashida, M. Fujiwara, N. Mizuochi and M. Nishikawa, Diam. Relat. Mater. 2021, 112, 108248.
[5] T. Yoshikawa, M. Liu, H. Miyake, R. Ieki, R. Kojima, Y. Makino, A. Tsurui, T. Mahiko and M. Nishikawa, Appl. Phys. Express 2021, 14, 055003.

The complex microbial community, e.g., biofilms residing in our oral cavity, have recognized the clinical significance, as they are typically the main causes of infections. Particularly, they show high resistance to conventional antibiotics, and alternatives including nanotechnology (e.g., bactericidal nanoparticles) are being intensively explored nowadays to provide more efficient therapeutics. The diamond nanoparticles, namely nanodiamonds (NDs), with many promising physico-chemical properties, have attracted significant growth of interest in their biomedical usage over recent years. Despite extensive works using NDs as labeling, imaging, sensing, and drug delivery agents in mammalian cells, only a limited number of studies have been conducted with bacterial (or fungal) cells. For example, the detonation NDs have been demonstrated to work as an effective antibacterial agent against planktonic cells (free-floating state) in the most studied model system Escherichia coli. However, little is known about the behaviors of NDs against biofilms (sessile state). Contrary to the commonly used detonation NDs, the promising (ultrapure, robust, biocompatible, and fluorescent) high-pressure high-temperature (HPHT) counterpart with stable color centers has been chosen in the current study. Here, for the first time, we have performed systematic microbiological studies of high-quality HPHT NDs on several oral and systemically important pathogens. Those “on purpose” chosen microorganisms include fungi (Candida albicans and Candida glabrata) and bacteria (Streptococcus mutans and Porphyromonas gingivalis), all of which are known to cause common human oral diseases. From the determined sub-inhibitory concentration by the routine test of HPHT NDs on planktonic cells, we have further investigated their capability of inhibition, as well as their role in gene regulation during biofilm formation. Furthermore, we also studied the effects of NDs on disrupting preformed biofilms, in a time and concentration dependent manner. These achievements further our mechanistic understanding of NDs on oral pathogens, paving the way for their clinical and translational applications such as drug carriers and/or additives in the human oral cavity.

While the field of nanomaterials design has benefited from the application of conventional machine learning methods by leveraging the correlations between structure and property variables, the outcomes from purely correlational studies lack actionability due to missing mechanistic insights. Statistical learning, particularly causal inference, can potentially provide access to more actionable insights by allowing the discovery and verification of deeply obscured causal relationships between variables, using strong correlations as starting points. In this presentation interpretable multi-target machine learning will be used to identify simultaneous correlations between the charge transfer properties of diamond nanoparticles, as a basis for statistical learning. Using Bayesian inference, directed graph models will be developed to predict causal pathways characteristic of the mechanisms responsible for the ionization potential the electron affinity, the electron band gap and the thermodynamic probability, and compare the likelihood that tuning a property via one causal path will impact another.

The unique properties of negatively-charged Nitrogen-Vacancy (NV^-) defect in diamond, make nanodiamonds with NV^- defects attractive for various applications. One of the important properties of NV^- centers is the possibility to efficiently initialize them in the m_s = 0 state at room temperature up to a very high degree (>90%) by illumination with green light. Using one of the dynamic nuclear spin polarization (DNP) techniques the polarization of NV^- centers can be transferred to surrounding nuclear spins, increasing the polarization of nuclear spins beyond thermal equilibrium. The advantage of nanodiamonds is their high surface to volume ratio. This provides an opportunity for efficient transfer of the nuclear polarization from inside of the diamond particle to external target nuclear spins. Therefore, it is expected that nanodiamonds with NV^- centers can be efficiently used as polarized magnetic resonance imaging (MRI) contrast agents.¹
One of the most important factors for the success of realization of NDs as hyperpolarized MRI agents is the possibility to achieve the properties of diamonds material that would fulfil the requirement for the efficient polarization transfer from NV^- centers to nuclear spins inside and outside of diamond particles. Those properties include high NV^- concentration, good spin properties of NV^- centers and nuclear spins, and tailored ¹³C composition. The desirable nanodiamonds properties can be achieved by improving synthesis and treatment techniques, with the help of careful characterization.
We show that simultaneous electron irradiation and annealing, with adjusted irradiation dose, provide a high conversion efficiency of substitutional nitrogen (P1 center) to NV^- defects in diamond powder². The presence of P1 defects, which constitute a noise source in the diamond lattice, is undesirable. Therefore, high conversion efficiency of P1 centers to NV^- defects, without important creation of other irradiation-induced defects, is also beneficial for spin properties both, of NV centers and ¹³C nuclear spins.
Having tailored ¹³C concentration, it is possible to increase the hyperpolarized signal³. Using the high pressure high temperature (HPHT) growth method, we synthesized diamond particles (20 nm to 2 µm) with different ¹³C content (5-30 %).⁴ To transfer the nuclear polarization from nuclear spins located inside of diamond particles to nuclear spins outside diamond, we also synthesized “core-shell” particles, where nanodiamonds with a natural (1.1%) abundance of ¹³C doped with NV centers are covered with a diamond layer with ¹³C content close to 100%.⁵ The synthesized material was analyzed with Scanning Electron Microscopy as well as Electronic Paramagnetic Resonance (EPR), Nuclear Magnetic Resonance (NMR) and Optically Detected Magnetic Resonance spectroscopy.
As a first step towards the realization of DNP techniques in nanodiamonds, we used micro-sized diamond material with improved properties to demonstrate the implementation of nuclear hyperpolarization, using a combined EPR-NMR system.

References:
1) A. Ajoy, K. Liu, R. Nazaryan, X. Lv, P. R. Zangara, B. Safvati, G. Wang, D. Arnold, G. Li, A. Lin, et al., Scien. Advan. 4 (2018).
2) Y. Mindarava, R. Blinder, C. Laube, W. Knolle, B. Abel, C. Jentgens, J. Isoya, J. Scheuer, J. Lang, I. Schwartz, B. Naydenov, F. Jelezko, Carbon 170 (2020).
3) A. J. Parker, K. Jeong, C. E. Avalos, B. J. M. Hausmann, C. C. Vassiliou, A. Pines, J. P. King, Phys. Rev. B 100 (2019).
4) Y. Mindarava, R. Blinder, Y. Liu, J. Scheuer, J. Lang, V. Agafonov, V. A. Davydov, C. Laube, W. Knolle, B. Abel, B. Naydenov, F. Jelezko, Carbon 165 (2020).
5) Y. Mindarava, R. Blinder, V. A. Davydov, M. Zaghrioui, V. N. Agafonov, C. Autret, P. Balasubramanian, R. Gonzalez, F. Jelezko, submitted.

We [1] have calculated the proton affinity (PA) and gas phase basicity (GPB) values of diamantane, triamantane, particular isomers of tetramantane and pentamantane, and then some significantly larger diamondoid molecules that are essentially globular, ranging up in size from containing 51 carbon atoms to containing 131 carbon atoms (and terminated on their surfaces with H atoms in C-H bonds). I'll discuss the PA and GPB values, atomic charge distribution in neutral diamondoids vs charged products by Bader charge analysis, and calculated NMR spectra (for example) for the charged products. To the best of our knowledge, only diamantane has been "protonated" and this was not done in the gas phase but in solution phase by Olah and Lukas using magic acid [2], in which they observed C14H20 + H+ yields C14H19+ plus H2(g). Their reported NMR spectrum is compared with our calculated spectra for a number of different C14H19+ isomers that we find as products of the above reaction (on the isolated gas phase molecule, and per calculations). In the lab, we are now preparing carborane acid(s), thus we expect to contact diamondoids, starting with diamantane, with carborane acid to find out if proton transfer occurs and to study the products. Future studies will involve larger diamondoid molecules such as perhaps through particular isomers of pentamantane, and also exposure of certain nanodiamond particles to carborane acids as well. I appreciate support from IBS BS-R019-D1. [1] Dulce C. Camacho Mojica, Jong-Kwon Ha, Seung Kyu Min, Robert Vianello, and Rodney S. Ruoff. Proton affinity and gas phase basicity of diamondoid molecules: diamantane to C₁₃₁H₁₁₆. Physical Chemistry Chemical Physics (2021) (under review). [2] Olah, G. A.; Lukas, J., Stable Carbonium Ions. 54. Protonation of and Hydride Ion Abstraction from Cycloalkanes and Polycycloalkanes in Fluorosulfonic Acid-Antimony Pentafluoride. J Am Chem Soc 1968, 90 (4), 933-938.

Clinical evidence suggests a strong association between type 2 diabetes (T2D) and Alzheimer’s diseases (AD) with T2D patients having a significant higher risk of developing AD compared to non-diabetic individua’s. Both AD and T2D share the accumulation of aggregated beta amyloid (Ab) or human islet amylin (hIAPP) with the accumulation and deposition of the proteins resulting in cell dysfunction and death. Prevention of Ab and hIAPP aggregation can be accomplished with various compounds such as dopamine or heparin, reducing cytotoxicity by inhibiting and/or delaying protein aggregation.
We have recently investigated the action of diamond nanoparticles and of carbon quantum dots (CQDS) against Ab and hIAPP aggregation. Within the field of amyloidosis, CQDs derived by the hydrothermal carbonization of glucosamine using ethylenediamine as a passivating coating have shown to be in particular efficient as nano-inhibitors but more interestingly for the disintegration of Ab and hIAPP aggregates. Similar to amyloidosis, fibrillation of collagen I is prevented most strongly by positively charged CQDs. In combination with pulsed-laser illumination the destruction of type I collagen aggregates and vitreous opacities, arising from clumped collagen fibers within the vitreous body that cast shadows on the retina, could be achieved.
References:
A. Barras et al. Carbon quantum dots as a dual platform for the inhibition and light-based destruction of collagen fibers: implications for the treatment of eye floaters. Nanoscale Horizon, 2021, 6, 449-461

The X-ray photoemission (XPS) spectroscopy is a suitable technique to finely characterize the surface chemistry and the reactivity of nanodiamonds (ND) [1]. Nevertheless, the interpretation of XPS spectra needs to be carefully considered as the ND size becomes comparable to the photoelectrons inelastic mean free path in diamond, namely a few nanometers [2]. In that case, due to geometrical consideration, an enhancement of the carbon signal occurs, as reported by Baer et al [3].
In the present study, detonation nanodiamonds were annealed between 800 and 950°C under vacuum or argon atmospheres to form sp² carbon at their surface [4]. The monitoring by XPS of induced modifications versus the annealing temperature will be presented. Results will be then compared to HR-TEM, FTIR and Raman measurements. According to XPS, the part of sp² carbon rises up to 30% for detonation ND annealed at 1100 °C under vacuum. Looking to HR-TEM images, the graphitization is only limited to the first outer shell. This is explained by a nano effect which exalts the extreme surface chemistry of detonation ND by a factor of 2.5 in the C1s core level.
References
[1] Arnault, Diam. Relat. Mater. 84 (2018) 157
[2] Tanuma et al, Surf. Interface Anal. 43 (2011) 689
[3] Baer et al, J. Surf. Anal. 12 (2005) 101
[4] Ducrozet et al, Nanomaterials 11 (2021) 2671

The application of nanomaterials in the field of biomedicine depends strongly on the interaction of their surface with the surrounding medium, with proteins, saccharides and other components of physiological environments.
Undesired non-specific interactions can prevent the application of otherwise promising nanomaterials, e.g. due to the masking of originally intended functionalities, unwanted agglomeration of nanoparticles or due to issues with biocompatibility.
Here we report on strategies for the functionalization of diamond nanoparticles with different types of organic molecules that effectively suppress the formation of a protein corona originating from unspecific interactions of surface groups with serum proteins. This includes the grafting of zwitterionic moieties onto the nanodiamond particles. Further, using a similar approach, pyrene-based moieties can be established that enable the specific sensing of heavy metals in aqueous environments using functionalized nanodiamond.
Besides, surface modifications with different types of groups such as small peptides, saccharides and polyethers will be presented, that improve the colloidal properties of nanodiamond in physiological media. In vitro experiments with different cell types show the effectiveness of these approaches and allow for future studies of biomedical applications of these materials.

Motivation: According to the World Health Organization, more than 300,000 deaths occur each year as a consequence of burn injuries¹. Each year in Australia, over 8000 patients are hospitalised for burn injuries, with acute treatment costing over $106M¹. Assessing wound repair requires removal of the dressings, which is a painful, time-consuming process based on subjective visual observation of the wound, and is disruptive to healing. Hence there is a critical need to improve this process as wound monitoring has a key role in identifying progress or deterioration for optimal patient management.
Biomarkers of interest: Temperature and pH of wound surface are two vital indicators of wound healing and progression^2,3. A clinically diagnosed wound infection elevates the temperature by +3° C to +5° C compared to the healthy skin². The pH of wound fluids is found to rise³ prior to the onset of more vital signs of local infection. Strongly alkaline pH at the wound surface is known to enable the invasion of microorganisms into the tissue layers below the dermis. In contrast an acidic wound environment aids healing through protease activity, increased oxygen release and reduction in microbial growth.
Aim: Our work aims to develop a smart and biocompatible silk dressing, integrated with temperature and pH sensors, capable of monitoring early signs of infections via non-invasive light-based measurements.
Materials and methods
Diamond particles for temperature sensing - The nitrogen vaccancy centre (NV) in diamond is highly sensitive to temperature due to changes in its electron spin energy levels. Diamond micro and nanoparticles with NV centres can be used as photostable, biocompatible and non-invasive sensor of temperature changes. The temperature changes (down to millikelvin resolution) can be detected via fluorescence using the optically detected magnetic resonance technique⁴.
Organic fluorophore 5,6-carboxynapthofluorescein (CNF) can measure pH within a wound-relevant pH window of 6.5-8.0, with a high sensitivity of 0.2⁵. CNF is a ratiometric pH sensor and its emission spectrum changes with respect to pH, providing a measurement technique that is robust even when the intensity of the fluorescence varies significantly. The ratio of the emission peaks around 550nm (green) and 680 nm (red) is a function of pH.
Optically transparent silk fibroin performs the crucial role of encapsulating the two sensors whilst preserving their sensing capabilities and preventing their release (uptake) into the healthy cells and tissues. Transparency of silk dressings will also enable non-invasive optical coherence tomography imaging to assess wound repair, scar formation and healing progression.
Results: We have obtained preliminary results indicating that silk membranes embedded with nanodiamond sensors are able to monitor temperature changes in the wound relevant window of 32-40 °C⁴. The in vitro tests revealed that the surface of the hybrid diamond-silk membranes enables eukaryotic cells attachment and promotes their growth. When applied to an in vivo wound model, the hybrid membranes enabled healing and the presence of nanodiamonds did not cause adverse effects on wound healing and closure. The hybrid membranes were found to be highly biocidal towards major skin wound infecting bacteria, P. aeruginosa and E. coli. We have also established that the pH-sensitive fluorophore CNF can be encapsulated within a silk matrix to provide in vivo measurements of acidity or basicity in vivo⁵. Hence hybrid sensor embedded silk dressings can be used as a multifunctional platform for biosensing as well as provide a network of fibres that supports a healthy wound healing process.
[1] Australian Institute of Health and Welfare 2019.
[2] A Chanmugam, et al, Advances in Skin & Wound Care, 30 (9), 2017.
[3] S Ono, et al, Burns, 41 (4), 2015.
[4] A Khalid, et al, ACS Applied Materials & Interfaces, 12(43), 2020.
[5] A Khalid, et al, Sensor and actuators B. Chemicals, 311, 2020.

Individual color centers offer unique capabilities as versatile, nanoscale sensors. Most of these sensing capabilities rely on their electronic spin and its optical state read-out. Consequently, efficiently collecting color center fluorescence is important. For scanning probe-based sensing and imaging, we incorporate color centers close to the apex of conically shaped nanopillars. These nanostructures, manufactured in sophisticated top-down processes [1], enable scanning color centers near a sample and enhance fluorescence collection [2]. We also investigate the coupling of excitation laser light with different laser wavelengths into various nanopillar types and find significant enhancements of the excitation fields in the nanopillars [3].
We furthermore optimize color center-based sensing via optimal control approaches [4] and novel sensing modalities: Using numerical methods, we optimize spin manipulation via shaping microwave pulses and spin initialization using laser pulses with optimized duration and intensity. While magnetic sensing is our main application field, novel approaches to color center-based sensing are evolving using near field processes such as Förster resonance energy transfer (FRET). We recently realized FRET between nitrogen vacancy (NV) centers and a luminescent two-dimensional material, namely WSe₂ [5]. We will discuss recent advances in this field including approaches to manufacture hybrid nanostructures consisting of diamond and two-dimensional materials.
[1] M. Radtke et al. Micromachines, 10, 718 (2019)
[2] P. Fuchs et al., New Journal of Physics, 20, 125001 (2018)
[3] A. Hochstetter and E. Neu, AIP Advances, 11, 065006 (2021)
[4] P. Rembold et al., AVS Quantum Science 2, 024701 (2020)
[5] R. Nelz et al. Adv. Quantum Techn. 3, 1900088 (2019)

Iron is an essential yet toxic redox active element that is found in many cells, including neurons and glial cells. Although substantial efforts have been devoted to understanding the mechanisms behind the abnormal iron accumulation in the diseased neurons and cells [1,2]. Different technqiues, including scanning proton induced X-ray emission spectrometry, have been used to quantify iron in neurons and glial cells [3]; however, most are incapable of high spatial resolution imaging inside a single cell. Diamond quantum sensors based on nitrogen vacancy (NV) centers have emerged as a powerful tool for detecting magnetic signal in iron-containing biological samples with a good combination of spatial resolution and sensitivity [4,5]. Cytochrome C (Cyt. C) is iron-containing biomolecule that plays an important role in the electron transport chain of mitochondria and it is in the Fe(III) paramagnetic state under ambient conditions. We report measurements of Cyt C under different concentrations and locations of the 10-nm NV doped diamond chip. We show a reduction of the NV relaxation time T₁ from few milliseconds to hundreds of microseconds, explained by the spin noise from the intracellular iron spins. We then discuss plans of imaging Cyt C and other iron-containing biomolecules and cells on nanostructured diamond chip integrated with dielectric gratings. [1] S. Oshiro, Adv. in Pharm. Sci. 378278 (2011). [2] R. Ward, et al., The Lancet. Neur. 13(10), 1045 (2014). [3] A. Reinert, et al., 20(1), 25 (2019). [4] P. Wang, et al., Sci. Adv. 5(4), eaau8038 (2019). [5] I. Fescenko, A. Laraoui, et al., Phy. Rev. App. 11(3), 034029 (2019).
Acknowledgment: This material is based upon work supported by the National Science Foundation/EPSCoR RII Track-1: Emergent Quantum Materials and Technologies (EQUATE), Award OIA-2044049. The research was performed in part in the Nebraska Nanoscale Facility: National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience (and/or NERCF), which are supported by the National Science Foundation under Award ECCS: 2025298, and the Nebraska Research Initiative.

A particularly interesting application of diamond based quantum sensing is the detection of nuclear magnetic resonance on nanometer scales, including the detection of individual nuclear spins or small ensembles of external nuclear spins. Single nitrogen vacancy (NV) color centers in diamond currently have sufficient sensitivity for detecting single external nuclear spins and resolve their position within a few angstroms. The ability to bring the sensor close to biomolecules by implantation of single NV centers and attachment of proteins to the surface of diamond enabled the first proof of principle demonstration signle molecule NMR. However, for that purpose, NV magnetometers must reach spectral resolutions comparable to that of conventional solution state NMR. New techniques for this purpose will be discussed. We will also pese t NV sensing experiments using colour centres in nanodiamonds

With its unique quantum features at room temperature, NV center has been recognized as a promising candidate for many applications in diverse fields. For instance, contrast-enhanced imaging has been achieved based on spin-dependent fluorescence of NV center, which is modulated by applied microwave fields or magnetic fields. Nevertheless, another intrinsic feature of NV center (i.e., polarization-selective excitation) seems to be underestimated in actual applications. For example, contrast-enhanced imaging also can be achieved based on this property. Here, we propose the linear polarization modulation (LPM) method to achieve contrast-enhanced imaging in model systems and living cells. Particularly, we would like to emphasize two advantages of LPM method: 1) high contrast, and 2) wide accessibility. Specifically, the observed contrast for a single NV center is approximately 10-90%, while that for ensemble NV centers is on the order of 20-60%. One should notice that our all-optical method is well fitted with a standard fluorescence microscope with slight modification, being easy for implementation. Therefore, this study paves the way for wider accessibility of NV centers in actual imaging applications.

Novel electrically conductive/Li-corrosion resistant/low-cost N atoms-grain boundaries incorporated ultrananocrystalline diamond (N-UNCD) coating provides excellent chemically robust encapsulation of commercial natural graphite (NG)/copper (Cu) anodes for Li-ion batteries (LIB), providing a solution to the problem of chemical degradation of the NG layer in LIBs’ NG-Cu anodes, due to Li-induced corrosion, via LiC₆, LiC₁₂, Li C₂₄ formation, as shown by XRD analysis in our prior R & D.
One key component of the R & D to be discussed in the presentation relates to the development of two processes to grow electrically conductive/Li-ion corrosion resistant N-UNCD coating on commercial NG/Cu anodes used in current Li-ion batteries, namely: 1) Microwave plasma chemical vapor deposition (MPCVD) process with Ar/CH₄/N₂ gas flow into a vacuum system, coupling 2000 Wats microwave power, creationg a plasma that cracks the CH₄ molecules producing a unique mixture of C₂ dimers and CHx (x=1, 2, 3) species, which react chemically on the surface of the NG layer heated to temperatures in the range 700-800 C, inducing the growth of N-UNCD encapsulating coating; 2) Hot Filament Chemical Vapor Deposition (HFCVD), featuring an array of parallel tungsten filaments, heated to ~2300 C, cracking CH₄ molecules flown in a H₂/ CH₄/Ar/N₂ gas mixture, reacting chemically on the NG/Cu anode on a holder heated to ~ 700 C. The research demonstrated that the N-UNCD coating grown on the NG layer of the NG/CU anode enables good conductivity of both electrons and Li-ions while exhibiting outstanding inertness to electrochemical Li-induced corrosion, and mechanical strength, resulting in the formation of robust SEI films, as shown by SEM and HRTEM analysis, effectively eliminating unceasingly cracking of SEI, exposure of fresh anode surface in commerecial NG/Cu anodes, resulting in repairing of the SEI by electrochemical reduction of the electrolyte and the formation of additional SEI compounds, which increase the impedance for the lithium ion diffusion and causes the electrolyte to be prematurely depleted. Results on Capacity Energy vs Charge/Discharge Cycles will be presented for three types of LIBs: 1) LIB with commercial NG/Cu anode, 2) LIB with conventional UNCD-coating on NG/CU anode, and 3) LIB with electrically conductive Li-corrosion resistant N-UNCD-coated NG/Cu anode, all of which show that LIBs with N-UNCD-coated anodes provide stable Capacity Energy with practically no degradation up to 3000 Charge/Discharge Cycles, in comparison with the other Test LIBs, showing the superior performance of the LIBs with N-UNCD-coated commercial NG/Cu anodes.
Also, new preliminary data will be presented showing that insulating/corrosion resistant UNCD coating, grown by MPCVD and by HFCVD, can be used to coat Aluminum metal, with a template layer on the surface, to enable grwoth of efficient / dense / pin-hole free UNCD coating, thus enabling to use Al as the less expensive/lighter metal for LIBs’ cases, with the inner walls protected from Li corrosion by the Li-corrosion resistant UNCD coating.
Detailed XPS analysis provided key information to understand the chemical link between N and C atoms in the N-UNCD coating on NG layers, to understand the chemical performance in relation to interaction with Li ions.

Color centres in diamond have emerged as promising candidates for emerging applications in quantum photonics, quantum information and quantum sensing. Specifically, group IV defects in diamond – namely the silicon vacancy (SiV), germanium vacancy (GeV) and tin vacancy (SnV) color centers are attracting an increased attention due to their favourable optical properties. These defects possess a very narrow linewidth and an inversion symmetry, that makes these defects less sensitive to local fluctuation in electric fields. An additional advantage of group IV defects is their high Debye-Waller factor that is manifested in a significant portion of the emission being concentrated in the zero phonon line.
In this talk I will discuss emerging applications utilising these defects - namely nanoscale thermometry. I will show two distinct modalities to harness temperature sensing with diamond color centres. The first, would be based on anti-stokes excitation of color centres, that enables high resolution sensing, down to a single defect level. In the second, I will show the potential of “single shot” temperature readout employing purely optical means, with spatial nanoscale resolution.
Overall, I will discuss an emerging topic of nanoscale optical thermometry employing color centres in diamond and nanodiamonds.