NV(-) Centers in Diamond as Qubits for Local Sensing of Rotational and Translational Mobilities of Active Proteins

Nitrogen- vacancy (NV) centers in nanodiamonds (10 to 100 nm diameter, FND) can be applied in biotechnology as single fluorescent quantum sensors. They react sensitively to changes in their environment, such as magnetic fields, temperature, or the presence of radical species. The extraordinary photo-physical properties such as very high photo-stability and non-blinking behavior allow for optical detection of magnetic resonance due to the NV triplet spin states. For a targeted interaction, the surface of nanodiamonds can be tailored e.g for specific binding to biological entities and can be modified to prevent non-specific interactions.[1,2] Here we want to exploit the single-spin properties of the luminescent NV-center in diamonds to reveal the dynamics of an active biological protein complex (FoF1-ATP synthase) at physiological conditions with highest spatio-temporal resolution. Enzyme dynamics include (A) ATP-driven subunit rotation and (B) reversible elastic deformation.<br/>In order to specifically bind the respective protein, the surface of the FNDs needs to be modified. We have explored different linker strategies including the grafting of aryl moieties with clickable terminal groups, the use of oligo ethylenglycol spacers with different terminal groups and the binding via biotin/streptavidin. Here we will report on the effect of different linker architectures on the colloidal properties under physiological conditions, the influence on the ratio of NV(0) vs. NV(-) centers and the brightness of the particles for detection in the ABEL trap.<br/>We will also present the characterization of individual nanodiamonds in solution. Using our confocal anti-Brownian electro-kinetic trap (ABEL trap) microscope we determine molecular brightness, spectral ratio and multi-exponential fluorescence lifetimes, but also diffusion coefficient and surface charge for each nanodiamond.<br/>This research has received funding from the Carl Zeiss Foundation as a QPhoton project.<br/>[1] E. Mayerhoefer, A. Krueger, Acc. Chem. Res. 2022, <i>55</i>, 3594.<br/>[2] A. Sigaeva, V. Merz, R. Sharmin, R. Schirhagl, A. Krueger, <i>J. Mater. Chem C </i><b>2023</b>, <i>11</i>, 6642.