A biocompatible workflow for in vivo spin imaging using charge-engineered polyglycerol nanodiamonds

Surface condition critically influences the biological labeling and performance of nanodiamond (ND) quantum sensors hosting nitrogen-vacancy (NV) spins. Polyglycerol (PG) grafting improves colloidal stability and suppresses nonspecific biomolecular adsorption, but can also reduce intestinal retention, making sufficient ND loading a key challenge for in vivo optically detected magnetic resonance (ODMR) imaging. Here, we introduce PG-grafted NDs with different terminal groups,–COOH, SO3Na, and NH2, to investigate charge-dependent biocompatibility for whole-intestinal ODMR imaging in Caenorhabditis elegans (C. elegans). Positively charged PG-NH2 NDs exhibit the highest intestinal retention in C. elegans without detectable toxicity, while maintaining bright fluorescence and stable NV spin signals. Combined with an adaptive masking algorithm to remove halo artifacts resulting from strong fluorescence, this labeling strategy enables reliable two-dimensional in vivo spin-active fluorescence imaging over the entire worm body. These findings identify surface-charge engineering of PG-grafted NDs as a practical strategy for establishing bright and biocompatible workflows for quantum-sensor-based bioimaging.