Quantum-enabled electrochemical sensing of redox-driven nitrogen-vacancy charge state dynamics

Redox signaling, fundamental to cellular processes and implicated in disease, involves dynamic electron transfer events that are challenging to probe within complex biological environments. This study introduces an innovative quantum sensing platform for biological electrochemistry. We demonstrate its capacity for real-time investigation of the redox-driven nitrogen-vacancy (NV) center charge state dynamics in fluorescent nanodiamonds (fNDs). The platform integrates disposable indium tin oxide screen-printed electrodes with inverted light microscopy, enabling simultaneous electrochemical control (cyclic voltammetry and amperometry) and optical monitoring of fND photoluminescence (PL). We show that varying electrochemical potentials directly modulate fND PL intensity, reflecting NV charge state transitions, and that interaction with the well-characterized electron-transferring protein, Cytochrome C (Cyt-c), results in a reversed PL response, indicating electron exchange. Importantly, the platform’s functionality in human serum (HS) is demonstrated through Cyt-c detection at both 5-fold and 2-fold dilutions, illustrating the performance achievable in the presence of a biological matrix. Overall, this simple quantum sensing approach, integrating electrochemical control and optical monitoring on a disposable, microscopy-compatible platform, offers a significant advance for probing biological redox processes, with the potential to enable future spatially resolved studies of cellular signaling and to inform new diagnostic strategies.