Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds
Jan Bartoň, Michal Gulka, Ján Tarábek, Yuliya Mindarava, Zhenyu Wang, Jiří Schimer, Helena Raabová, Jan Bednář, Martin B. Plenio, Fedor Jelezko, Miloš Nesládek, Petr Cígler
Abstract
Biocompatible nanoscale probes for sensitive detection of paramagnetic species and molecules associated with their (bio)chemical transformations would provide a desirable tool for a better understanding of cellular redox processes. Here, we describe an analytical tool based on quantum sensing techniques. We magnetically coupled negatively charged nitrogen-vacancy (NV) centers in nanodiamonds (NDs) with nitroxide radicals present in a bioinert polymer coating of the NDs. We demonstrated that the T1 spin relaxation time of the NV centers is very sensitive to the number of nitroxide radicals, with a resolution down to ∼10 spins per ND (detection of approximately 10–23 mol in a localized volume). The detection is based on T1 shortening upon the radical attachment, and we propose a theoretical model describing this phenomenon. We further show that this colloidally stable, water-soluble system can be used dynamically for spatiotemporal readout of a redox chemical process (oxidation of ascorbic acid) occurring near the ND surface in an aqueous environment under ambient conditions.