Toward Subcellular Action Potential Detection with Nanodiamond Quantum Magnetometry.

Quantum sensing with nitrogen vacancy (NV) defects in diamond enables detection of extremely small changes in temperature, host material strain, and magnetic and electric fields. Action potential detection has previously been demonstrated with cardiac tissue and whole organisms using NV defects in bulk diamond crystals. Nanodiamonds (NDs) with NV defects were previously used as effective fluorescent markers, as they do not bleach under laser illumination like conventional fluorescent dyes. Subcellular-level action potential recording with NDs is yet to be demonstrated. Here, we report our results on the confocal imaging of NDs and the feasibility of optically detected magnetic resonance (ODMR) experiments with Cath.-a-differentiated (CAD) mouse brain cells. 10 nm and 60 nm NDs were shown to diffuse into cells within 30 min with no additional surface modification, as confirmed with confocal imaging. In contrast, 100 nm and 140 nm NDs were observed to remain localized on the cell surface. ND photoluminescence (PL) signals did not bleach over the course of 5 h long imaging studies. ODMR technique was used to detect externally applied millitesla-level magnetic fields with NDs in cell solutions. In summary, NDs were shown to be effective, non-bleaching fluorescent markers in mouse brain cells, with further potential for use in action potential recording at the subcellular level.