Towards Application of Nanodiamonds for in-situ Monitoring of Radicals in Liquid Phase Chemical Reactions

TL;DR

This paper demonstrates the use of nitrogen-vacancy centers in nanodiamonds to detect short-lived radicals in liquid reactions in-situ, with high sensitivity and potential for real-time monitoring.

Contribution

It introduces a novel application of NV center-based T1 relaxometry for in-situ radical detection in liquid-phase reactions.

Findings

Successfully detected TEMPO radicals using NV center relaxometry.

Observed concentration-dependent relaxation time shortening.

Achieved detection sensitivity in the nanomolar range.

Abstract

In many chemical reactions, short-lived radical intermediates play a crucial role, while detecting such short-lived species in-situ remains challenging. The optically readable electronic spin of nitrogen-vacancy (NV) centers in diamond is a nanoscale sensor for such radical species: its longitudinal spin relaxation time (T$_{1}$) reacts to magnetic fluctuations from the unpaired electrons of radical species in its local environment. In this setting, we demonstrate the successful in-situ detection of the nitroxide radical 2,2,6,6-Tetramethylpiperidinyloxyl (TEMPO) using NV center-based T$_1$ relaxometry after depositing nanodiamonds onto the inner wall of a glass cuvette. A significant concentration-dependent shortening of the relaxation time was observed, from $197\:\mu s \pm 21\:\mu s$ without radical to $66\:\mu s \pm 30\:\mu s$ at a concentration of 1 M TEMPO. The detection is sensitive in the nanomolar (nM) range and the determined signal-to-noise ratio is between 1.6 and 3.