Symposium BM5 : Materials for Biointegrated Photonic Systems

vivo optogenetics provides unique, powerful capabilities in the dissection of neural circuits that govern brain function. Conventional hardware for such studies, however, physically tethers the experimental animal to an external light source limiting the range of possible experiments. Emerging wireless options offer important capabilities that avoid some of these limitations, but the current size, bulk, weight, and area of coverage represent key disadvantages. Here, we describe materials and device designs for systems that exploit wireless, near-field power transfer and miniaturized, thin flexible optoelectronic implants, for complete optical control in a variety of behavioral paradigms. The devices combine subdermal magnetic coil antennas connected to microscale, injectable light emitting diodes, with demonstrated ability to operate at wavelengths ranging from ultraviolet to blue, green, yellow, and red. An external loop antenna allows robust, straightforward application in a multitude of behavioral apparatuses while retaining the ability to trigger a diverse range of stimulation parameters. The result is a readily mass-producible, user-friendly technology with broad potential in optogenetics, and demonstrated utility in animal studies of neural activity in the brain, spinal cord and peripheral nerves of the bladder.

Lasers are among the most powerful tools in the life sciences but their macroscopic size and sensitive optical components have so far prevented bio-integration for any practical application. Interfacing lasers with living matter requires miniaturized laser resonators and gain media which both need to be biocompatible. Various types of microscopic lasers have been reported [1], but it is not clear if any of these work at physiologically relevant conditions and how the light that they produce can be used.
Polymer microspheres doped with a fluorescent dye trap light by total internal reflection and the resulting whispering gallery modes (WGM) facilitate lasing upon optical pumping. Recently, we [2] and others [3] showed that these WGM microresonators can be internalized by live cells to enable intracellular lasing. Importantly, due to minute differences in size, each resonator features a characteristic lasing spectrum providing each cell with a unique barcode-type tag. To widen the applicability of intracellular lasers, efficient delivery of microresonators to a broad range of cell types is crucial.
Here, we demonstrate that treating the surface of WGM resonators strongly improves the efficiency of resonator delivery, enabling us to efficiently target primary cells from the nervous system as well as cancer and neuronal cell lines. We also demonstrate that WGM resonators facilitate cell tracking over several days and in particular we show that resonators remain inside the cells during cell division, providing strong evidence that the presence of the resonator does not impair cell function. We will demonstrate that the spectral information that characterizes each resonator bears a huge potential to realize a new generation of fast, robust and reliable cell tags. We envision that intracellular lasers can be used to explore the properties of individual cells among large cell populations which is critical to a number of important biological processes like morphogenesis, cancer metastasis, neuronal network development, and immune response.

[1] M. T. Hill and M. C. Gather, Nat. Photonics 8, 908 (2014).
[2] M. Schubert, A. Steude, P. Liehm, N. M. Kronenberg, M. Karl, E. C. Campbell, S. J. Powis, and M. C. Gather, Nano Lett. 15, 5647 (2015).
[3] M. Humar and S. Hyun Yun, Nat. Photonics 9, 572 (2015).

The idea behind bioresorbable electronic devices is the full decomposition of the device inside the patient’s body which prevents an additional intervention for removal after treatment. Organic light-emitting diodes (OLED)¹ and light-emitting electrochemical cells (LEC)² are optoelectronic thin film devices which could function as implantable light sources for biomedical sensing or treatments. Presently, bioresorbable substrates and electrodes are being widely investigated for many types of optoelectronic devices³, however, a bioresorbable composition of a light-emitting device is still to be demonstrated.
In this work we show that the polymer polycaprolactone⁴ (PCL) can be used as a bioresorbable ion solvating polymer in the active layer of a LEC in conjunction with a poly(phenylenevinylene) derivative as an emitter. We characterized the performance of the LECs as a function of PCL content through a comprehensive characterization of the film and the devices by atomic force microscopy, cyclic voltammetry, operational lifetime and impedance spectroscopy. Addition of PCL increased the ionic conductivity up to four orders of magnitude to 10^-7 S/cm to demonstrate its ion-solvating capabilities, reduced the turn-on voltage to 3.2 V and increased the lifetime to the order of 30 h operating above 150 cd/m² within 20 s of turn-on time. Furthermore, we introduce a vitamin-derived solution-processable small-molecule as a bioresorbable emitter. We studied its film forming properties and tested its application as an emitting layer in a regular OLED.

1. Tang C, VanSlyke S. Organic electroluminescent diodes. Applied Physics Letters. AIP; 1987;51(12):913–5.


2. Pei Q, Yu G, Zhang C, Yang Y, Heeger AJ. Polymer light-emitting electrochemical cells. Science. American Association for the Advancement of Science; 1995;269(5227):1086–8.


3. Irimia-Vladu M. “Green” electronics: biodegradable and biocompatible materials and devices for sustainable future. Chemical Society Reviews. Royal Society of Chemistry; 2014;43(2):588–610.


4. Woodruff MA, Hutmacher DW. The return of a forgotten polymer—polycaprolactone in the 21st century. Progress in Polymer Science. Elsevier; 2010;35(10):1217–56.

Organic light-emitting devices have become a big topic in modern research and are often discussed as a future leading technology because of their light weight, flexibility and solution processability.¹ In this work we are presenting an approach to connect organic electronics with the biological world by investigating devices based on bio-resorbable polymers. We show that those polymers do not only offer the possibility of new fields of applications by making the devices more bio-compatible but can also be used to improve the device performance.
In this work, we present light-emitting electrochemical cells (LEC) comprising of the bio-degradable polymer poly(lactic-co-glycolic acid) (PLGA). LECs consist of an emitter material and a polyelectrolyte, both mixed together in one active layer which is deposited between two electrodes. Applying an electric field at the electrodes leads to a dissociation of the cat- and anions of the electrolyte and consequently to a formation of highly doped regions at the contacts, which allows charge injection into the semiconductor material.^2,3 Here in, we utilized a poly(phenylvinylen) derived conjugated polymer as emitter material while the solid polymer electrolyte consists of (PLGA) and the organic salt tetrabutylammonium tetrafluorborate. The device performance was analyzed as a function of the weight ratios of the specific components for three different lactic:glycolic monomer ratios (85:15, 75:25, 65:35) of PLGA. In all three cases adding PLGA to the active layer leads to a significant improvement of the turn-on-time compared to reference devices without PLGA. This can be attributed to an increase in ionic conductivity which was measured by impedance spectroscopy. Increasing the amount of PLGA in the active layer shows that the improvement is limited by phase-separation, which was observed by fluorescent microscopy. The best devices showed turn-on-voltages of about 4.1V and a maximum luminance of 3800cd/m².


¹ Forrest, Stephen R: The path to ubiquitous and low-cost organic electronic appliances on plastic. Nature 428, 911-918 (2004).
² Edman, L., Bringing light to solid-state electrolytes: The polymer light-emitting electrochemical cell. Electrochemica acta 50, 3878-3885 (2005).
³ Hernandez-Sosa, Gerardo and Tekoglu, Serpil and Stolz, Sebastian and Eckstein, Ralph and Teusch, Claudia and Trapp, Jannik and Lemmer, Uli and Hamburger, Manuel and Mechau, Norman: The Compromises of Printing Organic Electronics: A Case Study of Gravure-Printed Light-Emitting Electrochemical Cells Advanced Materials 26, 3235-3240 (2014).

Silk protein is a natural biopolymer with intriguing properties, which are attractive for next generation bio-integrated electronic and photonic devices. The devices fabricated on silk protein substrates can be useful for implantable bioelectronics. The direct use of silk protein as a material, rather than the substrate, is attractive for bio-integrated device applications. However, as silk protein is an electrical insulator, it is essential to enhance its electrical conductivity along with modulation of optical properties by doping or combining the metal and semiconductor nanostructures for use in functional bio-electronic devices. Here, we present the negative photoconductive response of Bombyx mori silk protein fibroin hydrogels, triggered by Au nanoparticles. The process of silk protein solution from Bombyx mori cocoons is followed as degumming, dissolution and purification. In a typical synthesis process for Au-silk hydrogels, the formation of Au nanoparticles within the silk protein is mainly due to the reduction of Au⁺³ while interacting with the amine groups of silk protein polymer chains. The room temperature electrical conductivity of Au-silk nanocomposite hydrogels is found to be enhanced with the incorporation of Au nanoparticles over the silk protein sample without Au, due to the increased charge transporting networks through Au nanoparticles within the hydrogel. Au-silk lateral photoconductor devices prepared on interdigitated Pt electrodes show a unique negative photoconductive response under an illumination of 325 nm, with excitation energy higher than the characteristic plasmon resonance band of Au. The enhanced photoconductance yield in the hydrogels over silk protein is attributed to the photo-oxidation of amino groups in the β-pleated sheets of silk around the Au nanoparticles followed by the breaking of charge transport networks. Photoluminescence studies further confirm that the strong interaction between the amino acids within silk protein and Au nanoparticles play a crucial role in electrical transport. The Au-silk nanocomposite does not show any photoresponse under visible illumination because of the localization of excited charges in Au nanoparticles. The negative photoconductive response of hybrid Au-silk under UV illumination may pave the way towards the utilization of silk for future bio-photonic devices using metal nanoparticle platform.

Flexible electronics have a wide range of applications, especially as biomedical implants and wearable devices, due to their thin physical structure which offers minimally invasive clinical operations. Combined with optoelectronics, flexible devices could extend applications to advanced biomedical stimulations and recordings involving light such as, optogenetics and oximetry. Because light is the primary stimulation tool for optogenetics, optoelectronics can benefit from using transparent devices by precisely exposing light on the recording site through transparent electrodes. Recently, graphene was proved by many groups to be an excellent recording electrode, with low artifact levels and comparable recording performance to state-of-the-art metal-based electrodes. With high-transparency, -conductivity, and excellent mechanical properties, graphene electrodes were demonstrated to be potential metal counterparts for optogenetics stimulations, recordings, and imaging applications. However, as laser was used as light source for stimulation externally, the graphene devices without any internally mounted light source, lacked the capability of operating under fully implanted condition. Thus, our team built a multifunctional implantable system utilizing nitride-based microscale light-emitting diodes vertically stacked on top of graphene electrodes where light can pass through the transparent device. This is the first ever built simultaneously stimulating and recording electro-cortical (ECoG) system utilizing transparent graphene. Our preliminary results indicate the suitable use of LED/graphene hybrid as an implantable optogenetics tool that is capable of simultaneously stimulating and recording. Study of the effects and impacts from the hybrid device on the animal tissue and performing simple animal behavioral tests under fully implanted and healthy conditions remain as future tasks. The successful demonstration of graphene electrodes integrated with high-performance flexible optoelectronic devices in thin-film, flexible format has ascertained that the hybrid device can potentially be the building block of multifunctional optogenetics tools for various clinical operations.

We report on the fabrication and characterization of solar blind photodetectors based on Zn and Si doped and undoped epitaxial ( -201) oriented β-Ga₂O₃ thin films grown by MOCVD. Triethylgallium (TEGa), diethylzinc (DEZn) and silane (SiH₄) were used as precursors for Ga, Zn, and Si, respectively, and the epilayers were grown on sapphire substrates. The structure, surface morphology, composition and optical properties of the films were characterized by various techniques. Zn doping has increased the unit cell volume without affecting the epitaxy, while Si doping led to the formation of polycrystalline films with an additional phase. The surface quality of the doped films was reduced, but the dopants had no apparent effect on the band gap. Photodetector properties were measured by fabricating the films into metal-semiconductor-metal (MSM) interdigitated devices. As grown films have a large number of defects, resulting in detectors with enhanced internal gain and, hence, high spectral responsivity > 10³ A/W. All the devices showed solar blind selectivity with a cut off wavelength (λ_c) ~260 nm except for the device based on the Zn doped film which had a λ_c of ~285 nm. The red shift in λ_c for the Zn doped device could be related to defects resulting from the substitution of Zn on the Ga site. Post growth annealing in an oxygen atmosphere improved the quality of the films, leading to detectors with reduced dark current (~ nA to ~ pA) and an increased UV visible rejection ratio. The λ_c for the device based on Zn doped film was ~260 nm, suggesting a reduction in defects, but the extra phase in the Si-doped film remained even after annealing. At 20 V bias, the Zn doped Ga₂O₃ detector showed a responsivity of 210 A/W (at 232 nm) and a visible rejection ratio of 5x10⁴. Alternatively, for the undoped β-Ga₂O₃ detector these parameters were found to be five times and three times lower, respectively, suggesting that Zn doped β-Ga₂O₃ detectors have superior performance characteristics. These results provide a roadmap towards achieving high responsivity solar blind photodetectors based on Zn doped β-Ga₂O₃ epitaxial films, providing a solid foundation for future applications.

In this study, we report preparation, luminescence and targeting properties of CdSeTe quantum dots-folic acid-doxorubicin conjugates. A facile method was used to synthesize excellent quality CdSeTe quantum dots (QDs). High resolution transmission electron microscopy (HRTEM) investigation indicated that well separated 4 nm size crystalline QDs were produced. Photoluminescence (PL) study showed emission spectra of the QDs around 520 nm. QDs were first connected to folic acid (FA) using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-N-hydroxysuccinimide (EDC-NHS) chemistry. Doxorubicin (DOX) was then attached to folic acid-QD conjugates via a pH-sensitive hydrazone bond in order to provide the stability of the complex in systemic circulation and drug release in acidic environment inside cancer cells. A systematic investigation of the effect of QD, QD+FA, and QD+FA+DOX was conducted with HeLa (cervical epithelial) cancerous cells using confocal microscopy. Samples were excited at 488 nm and 520 nm with fluorescence emission collected at 525 ± 50 nm and 607 ± 36 nm respectively. The potential of the proposed conjugate in treatment of cancer was investigated.

We review hybrid flexible semiconductor nanomembrane based Si/InGaAs multi-band focal plane arrays based on PDMS transfer printing processes. Optical membrane sensors based on transfer printed photonic crytal membrane Fano resonance filters will also be discussed, for potential applications in bio-integrated photonic systems.

We report recent progress of ultraflexible organic photonic and electronic devices such as organic thin-film transistors (OTFTs), organic photodetectors (OPDs), and organic light-emitting diodes (OLEDs) that are manufactured on ultrathin plastic film with the thickness of 1 μm [1-4]. In particular, we report ultraflexible and conformable, three-color, highly efficient OLEDs and OPDs to realize photonic skins that introduce multiple electronic functionalities such as sensing and displays on the surface of human skin. By integrating green and red OLEDs and OPDs, we fabricated an ultraflexible reflective pulse oximeter. The device was laminated on a finger to measure the oxygen concentration of blood. This work is financially supported by JST/ERATO Bio-harmonized electronics project.

[1] M. Kaltenbrunner, et al., Nature 499, 458 (2013).
[2] M. S. White, et al., Nature Photonics 7, 811–816 (2013).
[3] M. Kaltenbrunner, et al., Nature Communications 3, 770 (2012).
[4] T. Yokota, et al., Science Advances, Vol. 2, no. 4, e1501856 (2016).

Interest in mechanical compliance has been motivated by the development of flexible electronics and mechanosensors. Specifically, studies and characterization of structural deformation at the fundamental scale can offer opportunities to improve the device sensitivity and spatiotemporal response. However, the development of precise measurement tools with the appropriate resolution remains a challenge. In this work we demonstrated a strain-gauge nanolaser by integrating an iron-nail-shaped rod-type PhC platform with a flexible and transparent polydimethylsiloxane (PDMS). Systematic control of the mechanical strain allows the modification of the photonic band structure, and the subsequent spectral behavior of the single-mode lasing peak serves as a strain-gauge mechanism. Photoluminescence measurements showed that a wide range of wavelength tuning (up to ~26 nm) with a sub-nanometer scale spectral resolution (<~0.6 nm) was achieved under repeatable and reversible positive (negative) strains of 11.8% (-9.9%). In addition, three-dimensional (3D) finite-difference time-domain (FDTD) simulations unambiguously reproduced the experimental observations, such as the lasing mode images and resonant wavelength shift. These simulated results support our quantitative analysis of the lasing threshold and strain sensitivity. We also demonstrated a locally interactive strain-based chemical pH sensor, showing robust reversible repeatability and temporal stability. Our technological approach that uses a band-edge lasing mode in the defect-free PhC structure enables detecting nanoscale alternations in arbitrary positions of the structure through the changes of lasing wavelength, and consequently it should be feasible to map local surface strains and deformations in many structures. Furthermore, the strain-gauge nanolaser or an array may be useful to deterministically differentiate particular chemical species and their shapes and concentrations in various chemical/biological systems.

Epidermal electronics is a class of noninvasive and unobstructive skin-mounted, ultrathin and ultrasoft electronics and sensors capable of physiological monitoring, environment sensing, electrical and thermal stimulation, and even controlled drug release. Their softness, conformability, and high performance have enabled unobstructive, continuous, and high fidelity measurement of physiological signals. The high cost of manpower, photomask, chemicals, vacuum equipment, and photolithographic facilities associated with its manufacture generally hinders their accessibility. We therefore invented a cost and time effective, dry and benchtop “cut-and-paste” process for the freeform and green manufacture of multimodal epidermal sensors using gold as the conductive and sensing material in the past [1]. To further reduce their thickness and visibility, we turn to atomically thin, optically transparent 2D materials such as graphene. CVD grown large area monolayer graphene is repeated transferred from copper substrate to ultra-thin, transparent polymer to form double-layer graphene. Using a mechanical cutter plotter, predesigned patterns can be formed in the graphene-polymer laminate which is supported by a releasable tape. Removing excessive regions can leave desirable patterns on the releasable tape. Printing patterned laminate on a temporary support can help the application of those ultrathin, transparent graphene sensors on human skin. Removing the temporary support can finally yield the transparent and stretchable graphene epidermal sensors on the skin. They are both mechanically and optically invisible and has been demonstrated to be able to measure electrophysiological signals, skin temperature, as well as skin hydration, which are all well compared with gold standards. These graphene-based epidermal conductors can also be applied as a wearable but invisible heater for thermal therapeutics.

[1] Yang et al, “Cut-and-Paste” Manufacture of Multiparametric Epidermal Sensor Systems, Advanced Materials 27(41), 6423-6430 (2015).

Blade coated polymer light-emitting diodes (PLEDs) with different colors are successfully demonstrated on one substrate for optoelectronic sensor applications. Flexible electronics are highly desirable for wearable application, in that they can conform well to human body, which in turn provides diverse usage and better signal quality [1]. Bladecoating solution based materials is an attractive printing scheme to fabricate electronic devices, considering its high throughput and simple method [2]. Here we use bladecoating to fabricate reproducible PLEDs with several colors. Surface energy patterning (SEP) is used to blade coat solution at desired areas. [3] This technique reduces the amount of solution wasted through the sides of the blade, as compared to bladecoating without SEP, which leads to highly homogeneous active layer film and relatively consistent device performance . Using this technique PLEDs with individual colors, red, green and near infrared (NIR) which are known colors that can be used to detect the condition of haemoglobin [4], are separately fabricated with blade coating; 5W from red and green, and 1.5W from NIR PLEDs respectively at 9V from PLED areas of 0.5cm². Luminous Efficacy and EQE of the PLEDs at 10mA/cm² were 4.4lm/W, 7.2% for Red, 14.2lm/W, 9.3% for Green, and 0.04lm/W, 3.6% for NIR. Also, SEP is further utilized to fabricate two PLEDs with different colors on one substrate with no decrease in the performance of the PLEDs. The PLEDs are used in conjunction with a photodiode to perform pulsating photoplethysmogram (PPG) measurements. Furthermore, with the multicolor PLEDs we successfully demonstrate oxygenation measurement. The scheme used here can be employed in large-scale, roll-to-roll, solution processed and flexible applications.

[1] Y. Khan, A.E. Ostfeld, C.M. Lochner, A. Pierre and A.C. Arias, Adv. Mater. 28, 4373-4395, 2016
[2] A. Pierre, I. Deckman, P.B. Lechêne and A.C. Arias, Adv. Mater. 27, 6411-6417, 2015
[3] A. Pierre, M. Sadeghi, M.M. Payne, A. Facchetti, J.E. Anthony and A.C. Arias, Adv. Mater. 26, 5722-5727, 2014.
[4] C.M. Lochner, Y. Khan, A. Pierre and A.C. Arias, Nat. Comm. 5, 5745, 2014.

We need new materials and/or new design principles for future soft electronics. In this talk, I will describe our recent success in using ultrathin gold nanowires as a new class of electronic skins (e-skin) materials. We demonstrated their applications in flexible transparent conductor and highly stretchable wearable sensors and supercapacitors. In particular, we could obtain highly stretchable nanopatches or tattoos which are body attachable and textile integratable, enabling monitoring of wrist pulses, hand gestures, body motions and controlling robotic arms in a wireless fashion. Time permitting, I will also briefly cover our recent work in the fabrication of flexible/stretchable sensors with bio-inspired design, ionic liquids, and copper nanowires.

Mechanically compliant photonic devices are useful for biophotonic applications such as epidermal sensing and minimally invasive implants. Here we present a coherent material selection, micro-mechanical engineering and optical design strategy which enables bendable, stretchable and multi-functional integrated photonics. By combining a multi-neutral-axis design with a Euler spiral waveguide layout, we demonstrated bendable and stretchable polymer and glass optical waveguides capable of sustaining sub-millimeter bending and 42% tensile strain up to thousands of deformation cycles. In addition to mechanically compliant passive photonic components, we have also developed a generic strategy for hybrid integration of active optoelectronic devices with flexible waveguides. Using the approach, we demonstrated flexible waveguide-integrated detectors with 0.35 A/W responsivity at 1550 nm wavelength and down to 0.7 mm bending radius. Application of these devices as sensitive strain gauges have been experimentally validated.

Biological pathways for the conversion of biomass to hydrocarbon biofuels or bioproducts rely upon microorganisms such as E. coli and S. cerevisiae capable of overproducing targeted small molecules. Directed evolution or random mutagenesis of the microbial strains has been widely studied in order to enhance production efficiency of specific metabolites and generate large strain libraries with 10⁷ - 10⁹ variants that must be screened for the most promising candidates. While high-performance liquid chromatography (HPLC) has been commonly utilized, this screening technique is low through-put and has limited screenable library sizes to less than 10³ variants. To address this challenge, we have developed an optically responsive screening platform in a standard 96-well microplate format [1] that allows for the high-throughput screening of biofuels and bioproducts in a reagentless manner. Specifically, the sensing platform consists of photonic crystals embedded in responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogels that are sensitive to the presence of alcohols and organic acids. By exploiting the unique thermal behavior of PNIPAm, the sensitivity of the photonic crystal hydrogel platform may be readily tuned by small changes in the detection temperature or the hydrogel composition. In this presentation, we will discuss the fundamental mechanisms by which our sensing platforms respond and transduce the response into a visual signal, as well as demonstrate their utility for the screening of microbial strain libraries that produce ethanol, lactic acid, and succinic acid.

[1] Sukwon Jung, Joel L. Kaar and Mark P. Stoykovich, “Design and Functionalization of Responsive Hydrogels for Photonic Crystal Biosensors”, Molecular Systems Design and Engineering, 2016, DOI: 10.1039/c6me00031b.

Diverse and tunable mechanical actuations in response to environmental stimuli is essential for various emerging applications, such as biosonsors, smart optical systems and microelectromechanical systems. The visible light is easy for access, convenience for operation and represents an ideal stimulus, but previous photo-responsive actuators limited by slow response speed, small displacement and simple deformation, which hindered their abovementioned applications. A general and effective strategy is inspired by mimicking the microscopic structure in plants that are able to generate rapid, large and diverse mechanical motions, in which the orientation of cellulose fibrils embedded in a matrix of hemicellulose, lignin, pectin and structural proteins plays a key role.

Here, we have developed visible-light-responsive actuators with diverse and tunable deformations by embedding aligned carbon nanotubes in paraffin wax on a polyimide substrate. Photomechanical actuations from phototropic/apheliotropic bending to three-dimensional helical buckling are highly tunable with carbon nanotubes alignment and can be completed in milliseconds reversibly without detectable fatigue after 100,000 cycles. Furthermore, a new family of lightweight fiber-shaped electronic, such as solar cells and supercapacitors, have been developed and integrated with the photo-responsive actuators into intelligent electromechanical devices.

Surface instability such as wrinkles commonly occurs in various materials with a wide scope of dimensions. Herein, we introduce three types of moisture responsive wrinkling surfaces with different dynamics as exposed to high humid environment based on a bilayer structure. All the three surfaces are initially flat and forming wrinkles as moisturized but with different responsive behaviors upon being further moisturized, dried and re-moisturized. In the first responsive dynamics, the highly opaque wrinkling surface can be rapidly generated as being moisturized and sustains for ca. 30 s followed by rewinding to transparent flattening surface upon further moisture exposure. No wrinkling surface is created again upon being re-exposed to moisture. This allows the design of an intriguing moisture responsive encryption device with the capability of “erase after read”. In the second dynamics, the wrinkling surface can be rapidly generated as being moisturized and keeps stable regardless of moisture exposure time. Upon drying, the winkles can release back to the original flattening surface. The wrinkling and flattening surface can be repeatedly and reversibly created upon multiple dry/moisture cycles. A corresponding novel application of breathing activated anti-counterfeit tab is demonstrated. In the third dynamics system, the wrinkling surface can be generated as being moisturized and keeps stable in moisturized and dried state. This surface can be applied as a water indicator for electronic circuit, anti-glare surface, and optical diffusor.

We here present a novel method for direct-writing functional materials such as metals, dielectrics, semiconductors, and biomolecules into 3-D patterns with 100nm resolution over millimeter length scales. In our method, using a two-photon microscope, chosen chemical moieties are first patterned at defined 3D locations throughout a polyelectrolyte hydrogel. Subsequently, these reactive moieties are used as anchors for the attachment of functional materials to the hydrogel backbone. The hydrogel is then shrunken isotropically by an order of magnitude in linear dimension, obtaining a final pattern with <100nm resolution. The final substrate is anhydrous, transparent, flexible, and has surface smoothness comparable to a silicon wafer. We explore the creation of conductive 3D metal patterns and 3D patterns with high refractive index contrast, with no limitations on the aspect ratio nor connectedness of the patterns. Finally, the process is both fast and inexpensive, and may thus facilitate the rapid prototyping and deployment of functional materials in photonics, electronics, biotechnology and nanotechnology.

Surface-enhanced Raman scattering (SERS) has been proven to exhibit high sensitivities and low detection limits for a wide variety of analytes in laboratory settings. Although hand-held Raman spectrometers enable on-site analysis, the facile fabrication of disposable sensors that can be mass produced is imperative. One technique for creating low-cost sensors—“nanoimprinting”—allows for control over the sensor topography and nanostructure spacing. In this work, the repeating nanostripe (template) was imprinted onto thin layers of epoxy resin. Compared to a planar surface, nanometric gratings, which are high surface area substrates, possess a higher density of hotspots and a greater number of surface interaction sites for molecules and biological analytes. Moreover, such periodic arrays (or gratings) have unique optical resonance features that have been shown to further enhance the SERS signal. The polymer arrays were briefly treated with oxygen plasma and then decorated with silver nanoparticles that were fabricated in situ on the imprinted surface using a simple, environmentally-friendly process. The nano-imprinted SERS substrates exhibited a competitive detection limit using rhodamine 6G (R6G). In addition, label-free detection of lipopolysaccharide (LPS), also known as endotoxin, was achieved, therefore demonstrating the versatility of the sensor. Finally, these sensors can be mass produced: one 4” silicon wafer template can produce at least 250 sensors and the imprinting process can be readily transitioned to flexible substrates for continuous roll-to-roll, high-volume manufacturing.

To enable optical fiber device for potentially bioinegrated photonic applications, such as bio-resorbable optical fiber in minimally invasive procedures for diagnosis and therapy, wearable sensing textile, organ-machine interfaces, many conventional optical fiber components might be modified to fulfill new requirements. These desire modifications may include the development of biodegradable optical fiber, flexible and miniaturized visible/infrared source, detector, and modulator, etc.

At present, this study aims to develop miniaturized fiber modulators (single crystalline LiNbO3) and bio-resorbable optic fibers (P2O5-based glass). A phosphate based glasses is chosen for the feasibility of fiber drawing and resorption behavior in phosphate-buffered saline (PBS; pH of 7.4) as function of various Li2O-Na2O-CaO-SrO concentrations. Regarding the development of modulator, a single-mode LiNbO3 optical fiber with ITO electrode was made successfully with the CO2 laser-heated pedestal growth technique. The fiber has a half-wave voltage (Vπ) of 7 V and effective electro-optic coefficient of 23 pm-V. A modulation performance comparison at 1.55 microns between the fiber and conventional LiNbO3 planar waveguide will be discussed in detail. Furthermore, potential applications of both optical fiber components in wearable photonic sensing for volatile compounds inside and outside skin will be presented.

The self-assembly of colloidal semiconductor nanoparticles, or quantum dots (QDs), with nanoscale precision enables us to exploit new collective properties for applications to optical detection, solar energy harvesting, biological research, etc. Various molecular linkers have been developed to functionalize the nanoparticles for self-assembly, but the precise control of interparticle distances is very challenging. DNA has demonstrated its usability in programming the spatial arrangement of molecules and nanoparticles in angstrom-to-nanometer scales, which makes the design and fabrication of complex functional structures possible. Here we report the aqueous-phase synthesis of highly luminescent cadmium chalcogenide CdTe/CdS QDs and their functionalization with single strand DNAs (ssDNA) for DNA-directed self-assembly in an aqueous solution. Water-soluble mercaptopropionic acids (MPA) were used to initially passivate the surface of CdTe core QDs. The MPA-capped CdTe QDs have an estimated diameter of 1-2 nm with a maximum absorption at 457 nm and green emission at 511 nm. After purification and dispersion in de-ionized water, the CdTe QDs are encapsulated with CdS shells. During the shell passivation, phosphorothioate oligonucleotides (ptDNA) are used for conjugation to the surface of QDs because the sulfur atoms in the ptDNA can be inserted into the CdS shells. The resulting phosphorothioate ssDNA-wrapped CdTe/CdS core/shell QDs exhibit a band-edge emission maximum at 604.4 nm. The prepared QD-ssDNA conjugates display a photoluminescence (PL) quantum yield of 39.7 % compared with the PL intensity of rhodamine 6G as a reference dye. The DNA-directed self-assembly of the QDs is confirmed by TEM analysis and gel electrophoresis. Furthermore, the hybridized structure of dye-modified ssDNA and ssDNA-functionalized QDs is prepared to study short- and long-range interactions between dyes and QDs in an aqueous solution for their applications as a Forster-type resonance energy transfer (FRET)-based fluorescence nanoprobe. The ssDNA-coated CdTe/CdS QDs and Cy5-labelled ssDNAs function as FRET donors and acceptors, respectively. When the target ssDNA are hybridized with both of the ssDNA-QDs and ssDNA-dye, the excitation of the QDs at 450 nm results in FRET excitation of Cy5, leading to the red emission from Cy5. We are currently investigating the optimization of experimental parameters for the ssDNA-QD assembly in order to obtain a higher FRET efficiency, which can increase the sensitivity of the nanoprobes. This research was supported by Nano Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science, ICT and Future Planning (MSIP) (2012M3A7B4049802).

Curcumin ((1,7-bis-(4-hidroxi-3-metoxifenil)-1,6-heptadieno-3,5-diona)), has several benefits related to medical applications, which are properties such as antitumor, antiviral, anti-inflammatory, antioxidant, anti-Alzheimer, among others, as can be seen in recent works. Curcumin compounds, isolated or blended with other anticancer drugs, has been cited as an inhibitor of several effects related to cancer cells. Clinical human trials shown curcumin is safe even at high dosages (12 g per day), with just a few side effects. In this work we present a study on the optical behavior of Curcumin for two solvents and solvent mixtures with distinct properties. The first solution were prepared using a concentration of 0.3 mM of Curcumin in ethanol (S1) and the second uses 0.34 mM of Curcumin in ultrapure water in basic media (few drops of NH₄OH; S2). We also studied a mixture solution with 70% of S1 and 30 % of S2 (S3). Optical absorbance measurements shows that S1 present a well defined band around 430 nm and a small band around 270 nm, related to the p®p* transition and a second broadband below 230 nm, related to s®s* transitions. The spectra of S2 shows a displacement of the p®p* bands, now centered at 335 and 260 nm. However, S3 behavior is different, showingS1 and S2 bands and, also, another band centered at 520 nm. This behavior is also present in photoluminescence results, realized with several excitation wavelengths. S1 does not change its waveform when we change the excitation from 260 nm to 430 nm. However, S2 present a 40 nm red shift when the excitation changes from 260 nm to 340 nm, suggesting distinct electronic processes. However, the most interesting result appears when we investigate S3, a solution that shows a carmine red color. The waveform completely changes when we chance the excitation wavelength, suggesting changes in the electronic structure of the sample, a behavior never watched before that brings our attention to the possibilities of build a tunable biological probe, something very interesting for biological applications.

Disordered nanoporous Ag nanomembranes (NPAg) (~100 nm thick) fabricated by a thermally-assisted dewetting method can increase the photoluminescence (PL) intensity of conjugated polymer thin films compared to those on planar Ag.¹ This is evidence that NPAg could serve as a platform in biocompatible, organic-conjugated-polymer-based, thin-film, light-emitting devices, which could be used as light sources for wearable optoelectronic biosensors, to achieve better light-extraction efficiency (η_ex) and, therefore, improve device efficiency.² Two possible mechanisms were proposed to explain the observed PL enhancement (E_PL): 1) the plasmonic properties of the nanopores could enhance the local electric field and, thus, enhance the radiative decay rate (Γ_r) and PL quantum efficiency (η_PL) of the polymer; 2) the polymer-filled pores might exhibit “waveguiding” behavior (WG) which could confine the emitted light to smaller emission cone and improve η_ex. However, the existence of these mechanisms and the extent to which they influence the E_PL remains unclear. Furthermore, the roles of nanopore diameter (D) and polymer chain organization on E_PL need to be further investigated to develop NPAg that could controllably enhance η_ex for a given conjugated polymer.
To study mechanisms of enhanced PL on NPAg in more detail, we applied poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT) (two conjugated polymers with similar absorption (400 - 600 nm) and emission wavelengths (600 - 800 nm), but different chain morphology and η_PL) to NPAg nanomembranes (1 - 3 cm²) with D of 0.38 ± 0.11 μm and pore densities (ρ) of either ~2.2×10⁷pores/cm² (B1) or ~4×10⁶ pores/cm² (B2). Small molecular weight MEH-PPV is believed to have random chain alignment in solid thin films and exhibit high η_PL, while P3HT showed dominantly ordered edge-on packing and exhibit very low η_PL.
Excitation-power-corrected, large-area, transmission-mode PL spectra indicated that MEH-PPV on both B1 and B2 NPAg showed larger E_PL (6.6 and 3.4, respectively) compared to that of P3HT (0.9 and 1.3, respectively). The spatially-resolved, reflection-mode PL lifetime studies proved that local electric field enhancement effects of nanopores didn’t affect Γ_r of either high or low η_PL polymer noticeably and was not the reason for the E_PL observed in the large area study. The fact that decreasing the ρ could reduce the E_PL of MEH-PPV significantly while slightly increase the E_PL of P3HT supported the aforementioned WG mechanism since better WG ability would be achieved from pores filled with more randomly-oriented polymer chains, i.e., MEH-PPV. Single pore studies on the relationship between D and E_PL are underway and a positive correlation between the D and E_PL of MEH-PPV is expected to further verify the existence of the WG mechanism.
1. Z. Shen et al., Adv. Funct. Mater. 2015, 25, 3302.
2. A. K. Bansal et al., Adv. Mater. 2015, 27, 7638.

Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure and pulse oxygenation have applications in both fitness monitoring and medical diagnostics. Pulse oximetry is a ubiquitous non-invasive medical sensing method for measuring pulse rate and arterial blood oxygenation and requires optoelectronic devices. Conventional pulse oximeters use expensive optoelectronic components that restrict sensing locations to fingertips or ear lobes due to their rigid form and area-scaling complexity. We have developed a flexible pulse oximeter sensor based on organic semiconducting materials and solution processing deposition, which are compatible with flexible substrates. Green (532nm) and red (626nm) organic light-emitting diodes (OLEDs) are used with an organic photodiode (OPD) sensitive at the same wavelengths of the peak emission of the OLEDs. The electronic materials are deposited from solution-processed materials using a combination of deposition techniques such as blade coating, screen-printing and inkjet printing. The all-organic optoelectronic oximeter sensor is calibrated and interfaced with conventional electronics at 1kHz, and the performance is compared with a commercially available oximeter. The organic sensor accurately measures pulse rate and oxygenation with errors of 1% and 2%, respectively. The long-term stability of the organic optoelectronic pulse oximeter, like most organic optoelectronics, is limited by the robustness of the encapsulation technology employed in its fabrication. With our encapsulation process, we see a 24% signal intensity decrease in the green and a 54% decrease in the red photoplethysmogram (PPG) signal over a 7-day time frame. While we observe a decline in signal intensity; the PPG signal remains intact and oxygenation values are obtained in the period of a week. We have also shown that the flexible form factors of the photodiodes reduce the noise in the measurement, caused by ambient light, due to the proximity of the skin. We will discuss other uses of this technology and strategies to obtain a truly flexible and wearable optoelectronic sensor.

Nanomembranes with outstanding electronic and photonic functionality are self-assembled into ultra-compact lab-in-a-tube architectures monolithically integrated on a single chip. Such functionalized microtubular systems provide an ideal platform to study single cell behavior in 2D confined channels mimicking natural capilliaries. In our case we concentrate in particular on mitosis and migration behavior of cancer and stem cells. Our microtubular devices include high sensitivity optofluidic microcavities, tubular impedence sensors for attomolar DNA concentration detection and first stimuli-responsive biomimetic integrated circuitry. New concepts towards 3D impedence cell tomography and chiral light generation in newly designed lab-in-a-tube systems will also be introduced.

Within mammalian nervous system billions of neurons connected by quadrillions of synapses are exchanging electrical, chemical and mechanical signals. Our ability to study this complexity is currently limited by the lack of technologies available for interrogating the nervous system across all of its signaling modalities without inducing foreign-body reaction.
Optogenetics, a method introduced a decade ago, enables optical manipulation of neural activity with millisecond precision. Unlike electrical stimulation, optical modulation permits simultaneous electrical recording of neural activity necessary for two-way communication with the neural circuits. To achieve minimally invasive bi-directional control of neurons in vivo, we have recently developed multifunctional flexible polymer-based fiber-probes. Produced via fiber-drawing techniques these devices incorporate optical waveguides, conductive electrodes, and microfluidic channels to allow for simultaneous electrical recording, optical stimulation and drug delivery into the brain of freely moving mice. Furthermore, these compliant structures allow for implantation into the spinal cord where they can be used for optical control of locomotor activity. Finally, fiber-drawing process can be applied to produce optoelectronic scaffolds allowing for topographic control of the developing neuronal processes and intimate electronic and optical interfaces with neural tissues integrated directly within these devices.

In the past decade, many progresses have been made in exploring novel materials for biophotonics devices. Silk fibroin, regenerated from aqueous solution, provides a new option for mechanically robust, biocompatible and bioresorbable optical system. On the other hand, as a key component for photonic systems, optical resonators, such as whispering gallery mode (WGM) microresonator, build an excellent platform for biosensing, chemical sensing, nanoparticle sensing and thermal sensing. In this work, we experimentally demonstrated all silk fibroin WGM microresonator by using solution-based molding and self assembly technique, with quality (Q) factor as high as 0.9×10⁵. We also present a high-sensitivity thermal sensor based this silk fibroin microtoroid with the sensitivity of 1.17 nm/K, that is 8 times higher than previous WGM resonantor based thermal sensors. The high sensitivity of the silk resonantor thermal sensor originates from the large thermal expansion coefficient of silk, which is three order of magnitude larger than that of silica. This protein-based microresonators on a flexible chip enable the fabrication of photonics system for biophotonic applications in vivo.

There is great potential for stimulating and recording from the peripheral nervous system and the organs that it controls to understand the neural circuits and organ function control, as well as to enable widespread deployment of these systems for variety of treatments. However, current technologies to do this are severely limited. Implantable stimulators are usually bulky because of the need for batteries and/or antennas/coils large enough to receive power with acceptable efficiency and at depth, and therefore require invasive surgery and multiple implanted cables connected to electrodes on specific nerves. Miniaturization, along with a robust and safe wireless connection, overcomes these limitations and also enables the possibility of having a network of sensor nodes for applications like multisite neural recording and stimulation. However, certain key applications such as optogenetics and electrical nerve stimulation require high power levels, typically 100 µW to a few mW, and this makes the design of the power delivery system even more challenging by simultaneously requiring high power density and efficiency. For this application we utilize acoustic waves in the ultrasonic range for power transfer since it has wavelengths comparable to the size of the implant, which enables focusing of the energy at the device site, leading to a higher link efficiency and lower heating in surrounding tissue as compared to RF powering techniques.

This contribution will describe recent work to incorporate pi-conjugated molecules of interest for organic electronics into self-assembling oligopeptides of interest for biomaterial applications. The assembly process leads to the formation of supramolecular polymers fashioned into 1-D nanomaterials ca. 10 nm in diameter. Using this general platform, a series of energy transport examples will be discussed, spanning transistor-based gating for carrier mobility, photonic activation for exciton transport, and the photonic creation of static electric fields. Prospects for using these hybrid electronic biomaterials to elicit biological adhesion or other specific responses in an externally tunable manner will be addressed.

Polyvinyl alcohol (PVA) and laponite nanocomposite coatings were fabricated, which exhibited iridescent color change in response to moisture exposure. Upon exposing the coatings to water vapor, a strong color reflection is achieved because of interference of light at the interface between multi-layers. Due to PVA’s sensitivity to water vapor and laponite’s contribution to the confinement of layered structure of the nanocoatings, a reversible color switch could be achieved. We also designed a patterned coating, in which a specific region was crosslinked to minimize the response to water vapor. Using this process, a fully reversible patterned coating was fabricated. Such a novel and low cost coating is expected to find applications in products in need of forgery prevention.

Photosystem I (PS I), the photosynthetic membrane protein complex, undergoes light activated (λ=680 nm) charge separation that drives unidirectional electron transfer with near unity quantum efficiency. The robust and efficient photoelectrochemical (PEC) activities of PS I make it an ideal candidate for incorporation into bio-hybrid photovoltaic and/or, optoelectronic devices. But, the first step towards rational design of such devices requires systematic electrochemical characterizations of uniform PS I thin films deposited onto self-assembled monolayer (SAM) and/or, nano-architectured surfaces. Our previous work had shown the use of detergent-mediated colloidal chemistry and electric field assisted assembly for surface immobilization of uniform PS I monolayer from aqueous buffer suspensions. ^[1-3] Our recent photoelectrochemical measurements indicate successful photocurrent generation from PS I monolayer on SAM/Au substrates. ^[4] Specifically, detailed electrochemistry measurements reveal a new mechanism wherein dissolved O₂ in aqueous electrolytes form a complex intermediate species with the soluble electron acceptor (Methyl Viologen, MV²⁺) that, in turn, becomes responsible for scavenging the electrons from the reduced terminals of PS I under aerobic conditions. These critical insights into the redox-mediated electron transfer pathways allow for rational design of electron scavengers in PS I-based PEC devices through systematic tuning of redox potentials for the intermediate mediators. Finally, PS I deposited on thiolated Ag nanostructures of truncated pyramids, with plasmonic peaks at λ~650-720 nm, indicate a 3 - 4 fold increase in the photocurrent generation when compared to the values from planar PS I/SAM(thiol)/Ag substrates. ^[5] Such photocurrent increments are attributed to the enhanced electric field and optical absorption resulting from the localized plasmon enhancement effects. These findings can provide a paradigm shift in the future design of PS I-based bio-hybrid constructs as photo-anodes in PEC cells and/or, plasmon coupled optoelectronic sensors and devices.
References:
[1] D. Mukherjee, M. Vaughn, B. Khomami, B. D. Bruce, Colloids and Surfaces B: Biointerfaces 2011, 88, 181
[2] D. Mukherjee, M. May, B. Khomami, J. Colloid Interface Sci. 2011, 358, 477.
[3] D. Mukherjee, M. May, M. Vaughn, B. D. Bruce, B. Khomami, Langmuir 2010, 26, 16048.
[4] T. H. Bennett, H. S. Niroomand, R. Pamu, I. Ivanov, D. Mukherjee, B. Khomami, Phys. Chem. Chem. Phys. 2016, 18, 8512.
[5] R. Pamu, B. Lawrie, R. Kalyanaraman, B. Khomami, D. Mukherjee, To Be Submitted. 2016.

In recent years, Tissue Engineering is utilized as an alternative approach for the organ transplantation. Success rate of tissue regeneration influenced by the biomaterials, cell sources, growth factors and scaffold fabrication. Design and precise fabrication of scaffolds are required to support cells to expand and migrate to 3D environment. Common scaffold fabrication techniques use heat, adhesives, molds or light. In this research, “inverse-photolithography” which is a light based fabrication technique was used to generate the scaffolds. In order to control the interior architecture of the scaffold “a single vertical strut” and “a y-shape” were fabricated with the 3D printer by using the dissolvable filament. Then, the strut and the y-shape were immersed into the photo-curable solution which is poly(ethylene glycol) diacrylate (PEGDA) and photoinitiator mixture. UV light with the 365nm wavelength was placed up-side down under the solution. Photocurable mixture was exposed to the UV light for 3 minutes to cure the entire scaffold. Solidified scaffold with the strut and y-shape inside was kept in the limonene solution. Limonene penetrated through the open ended strut and y-shape and it dissolved the 3D printed strut and y-shape away leaving the fabricated PEGDA based scaffolds. This preliminary research showcases, the 3D scaffolds with the controlled interior design, can be fabricated with the “inverse-photolithography” technique.