Bright Quantum-Grade Fluorescent Nanodiamonds
Keisuke Oshimi, Hitoshi Ishiwata, Hiromu Nakashima, Sara Mandić, Hina Kobayashi, Minori Teramoto, Hirokazu Tsuji, Yoshiki Nishibayashi, Yutaka Shikano, Toshu An, Masazumi Fujiwara
Abstract
High Resolution Image Download MS PowerPoint Slide Optically accessible spin-active nanomaterials are promising as quantum nanosensors for probing biological samples. However, achieving bioimaging-level brightness and high-quality spin properties for these materials is challenging and hinders their application in quantum biosensing. Here, we demonstrate bright fluorescent nanodiamonds (NDs) containing 0.6–1.3-ppm negatively charged nitrogen-vacancy (NV) centers by spin-environment engineering via enriching spin-less 12 C-carbon isotopes and reducing substitutional nitrogen spin impurities. The NDs, readily introduced into cultured cells, exhibited improved optically detected magnetic resonance (ODMR) spectra; peak splitting ( E ) was reduced by 2–3 MHz, and microwave excitation power required was 20 times lower to achieve a 3% ODMR contrast, comparable to that of conventional type-Ib NDs. They show average spin-relaxation times of T 1 = 0.68 ms and T 2 = 3.2 μs (1.6 ms and 5.4 μs maximum) that were 5- and 11-fold longer than those of type-Ib, respectively. Additionally, the extended T 2 relaxation times of these NDs enable shot-noise-limited temperature measurements with a sensitivity of approximately 0.28 K / Hz . The combination of bulk-like NV spin properties and enhanced fluorescence significantly improves the sensitivity of ND-based quantum sensors for biological applications.