These applications rely on ensembles of NV -centers in the vicinity of the diamond surface . Due to their large surface area, NV-rich, fluorescent nanodiamonds (NDs) are promising candidates for such applications . Moreover, NDs are biocompatible, and their surface can be functionalized to target specific cells or proteins . NDs can be internalized by living cells, thus probing the microenvironment in subcellular compartments . Furthermore, 13 C enrichment of NDs is desirable to improve the hyperpolarization efficiency for contrast agents, quantum sensing and magnetic resonance signal enhancement .