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

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.

Quantum monitoring of cellular metabolic activities in single mitochondria

“…This sequence is especially convenient because it does not require microwaves. The technique has already been used for several different applications including detection of gadolinium ( 39 ), magnetic structures ( 40 ), nanoparticles ( 41 – 43 ), and, most recently, free radicals ( 44 , 45 ). We demonstrate their use for monitoring metabolic activity in single cells or organelles.…”

Detection of Few Hydrogen Peroxide Molecules using Self-Reporting Fluorescent Nanodiamond Quantum Sensors

“…We considered that there were surface electrons at the ND surface, which made 𝑇 1 buffer smaller for smaller NDs. The amplitude variance of the magnetic noise produced by the OH or O2H radicals, 𝐵 ⊥ 2 = Σ 𝑗 𝐵 ⊥,𝑗 2 , is a sum of the terms due to each radical electron spin 36,42 𝐵 ⊥,𝑗 produced by the OH or O2H radicals, the increased decay rate due to the magnetic noise of the OH or O2H radicals is given by 36 1…”

“…So far, T1 relaxometry has been used for the detection of a range of paramagnetic spins such as gadolinium, 24,[34][35][36] ferritin, [37][38][39][40] manganese ions, 40,41 and most recently free radicals. 42,43 However, T1 relaxometry is insensitive to non-paramagnetic species such as H2O2.…”

SARS-CoV-2 Quantum Sensor Based on Nitrogen-Vacancy Centers in Diamond

“…In particular, paramagnetic molecules such as gadolinium (Gd) complexes can induce strong transverse magnetic noise and significantly reduce the NV spin relaxation time. 8 , 11 , 12 …”