Monitoring spin coherence of single nitrogen-vacancy centers in nanodiamonds during pH changes in aqueous buffer solutions

TL;DR

This study evaluates the stability of nitrogen-vacancy (NV) center-based nanodiamond quantum sensors in aqueous buffer solutions across a pH range of 4 to 11, demonstrating their potential for reliable quantum sensing during pH fluctuations.

Contribution

The paper introduces a method to monitor the spin coherence of single NV centers in nanodiamonds during pH changes, highlighting their stability and measurement accuracy in different buffer solutions.

Findings

NV centers maintain stable spin coherence times during pH changes

Resonance frequency fluctuations are within measurement error

The system enables observing individual NDs in various buffer solutions

Abstract

We report on sensing stability of nanodiamond (ND) quantum sensors in various pH aqueous buffer solutions for the two detection schemes of quantum decoherence spectroscopy and thermometry. The electron spin properties of single nitrogen-vacancy (NV) centers in 25-nm-sized NDs have been characterized by a spin-measurement compatible perfusion (SMCP) chamber where observing the same individual NDs in different buffer solutions is possible. With this system, we have determined the stability of the NV quantum sensors during the pH change from 4 to 11 as the fluctuations of +- 12% and +- 0.2 MHz for the spin coherence time ($T_2$) and the resonance frequency ($\omega_0$) of their mean values, which are comparable to the instrumental error of the measurement system. Here, we discuss the importance of characterizing the sensing stability during pH changes and how the present observations affect ND-based NV quantum sensing.