Surface Modification of Fluorescent Nanodiamond for Quantum Sensing

Developments in quantum sensing which surpass the capabilities of classical measurements will improve the understanding of complex events in molecular disease biology and enable new modalities for drug and biomarker discovery. The negatively charged nitrogen-vacancy (NV) center in fluorescent nanodiamond can sense local electromagnetic fields, free radicals, temperature, and pH with nanoscale resolution. However, charge transfer and electromagnetic noise from the particle’s surface destabilize negatively charged NV^- emitters and convert them to non-sensing, neutral NV0 centers. This effect is important because sensing has a strong dependence on distance, and thus the quality of shallow NVs relates to sensing characteristics. Additionally, at small particle sizes the fraction of destabilized NV centers near the surface becomes significant. Here we report results for conversion and stabilization of NV^- by plasma surface modification with fluorine and nitrogen groups to provide enrichment and stabilization of NV^-. The treatment is shown to be suitable for particles of differing sizes and initial surface chemistries, allowing for scalable production of nanodiamond particles adapted for quantum sensing applications.