Intranuclear Quantum Sensing with Fluorescent Nanodiamond Enabled by Electron-Irradiation and Surface-Chemical Optimization for Microinjection

Abstract Fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) centers are promising quantum sensors for intracellular measurements, yet nuclear applications remained out of reach because optically detected magnetic resonance (ODMR) signals are weak and capillary delivery is inefficient. This study addresses both constraints by optimizing the electron irradiation dose to balance NV creation and charge-state stability, and by grafting hyperbranched polyglycerol with terminal carboxyl groups (HPGCOOH) to suppress aggregation and prevent needle clogging. The optimized dose yields strong ODMR contrast while preserving fluorescence suitable for microscopy. HPGCOOH surfaces enable smooth and reproducible microinjection through fine capillaries. Using this strategy, the microinjection of ODMR-active FNDs into the nuclei of living COS7 cells is achieved, and clear intranuclear spectra comparable to cytoplasmic readouts are obtained. Furthermore, field-of-view temperature sensing across multiple cell nuclei is demonstrated, enabling quantitative and spatially resolved thermal mapping within the genomic environment. This methodology provides a practical route to nuclear quantum sensing and opens opportunities for nanoscale physicochemical measurements within the genomic environment. Competing Interest Statement The authors have declared no competing interest. Footnotes ↵* Email: yharada{at}protein.osaka-u.ac.jp Funding: This work was supported by Early-Career Scientists (19K16089 and 21K15053 to S.S.), Toyota Riken Scholar Program (to S.S.), Kyoto Technoscience Center (to S.S.), JST-FOREST Program (JPMJFR2428 to S.S.), JSPS KAKENHI (22H02583 and 24H02306 to Y.H., and 25K08446 to K.F.), MEXT Q-LEAP (JPMXS0120330644 to Y.H.), JST CREST (JPMJCR24B6 to Y.H.), and JSPS Postdoctoral Fellowship (PE23701 to A.G.).