Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds

TL;DR

This paper introduces a quantum sensing method using nitrogen-vacancy centers in nanodiamonds to detect and monitor redox chemical processes at the nanoscale with high sensitivity and real-time capability.

Contribution

It presents a novel nanoscale quantum sensor that detects paramagnetic radicals and monitors redox reactions dynamically in aqueous environments.

Findings

Sensitive detection of ~10 radicals per nanodiamond.

Real-time monitoring of redox processes like ascorbic acid oxidation.

Theoretical model explaining T1 relaxation changes due to radicals.

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 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 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.