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 ¹²C-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 T₁ = 0.68 ms and T₂ = 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 T₂ relaxation times of these NDs enable shot-noise-limited temperature measurements with a sensitivity of approximately 0.28K/Hz⎯⎯⎯⎯⎯√$0.28\mathrm{K}/\sqrt{\mathrm{Hz}}$$0.28\mathrm{K}/\sqrt{\mathrm{Hz}}$. The combination of bulk-like NV spin properties and enhanced fluorescence significantly improves the sensitivity of ND-based quantum sensors for biological applications.

中文翻译：

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明亮的量子级荧光纳米金刚石


光学可及的自旋活性纳米材料有望作为探测生物样品的量子纳米传感器。然而，为这些材料实现生物成像级别的亮度和高质量的自旋特性具有挑战性，并阻碍了它们在量子生物传感中的应用。在这里，我们通过自旋环境工程富集无 ¹² 自旋 C 碳同位素和减少取代氮自旋杂质，展示了含有 0.6-1.3-ppm 负电荷氮空位 （NV） 中心的明亮荧光纳米金刚石 （ND）。NDs 很容易引入培养细胞中，表现出改进的光学检测磁共振 （ODMR） 光谱;峰分裂 （E） 降低了 2-3 MHz，实现 3% ODMR 对比度所需的微波激发功率降低了 20 倍，与传统的 Ib 型 ND 相当。它们显示 T ₁ = 0.68 ms 和 T ₂ = 3.2 μs（最大 1.6 ms 和 5.4 μs）的平均自旋弛豫时间分别比 Ib 型长 5 倍和 11 倍。此外，这些 ND 的 T ₂ 弛豫时间延长，可实现散粒噪声限制的温度测量，灵敏度约为0.28K/ 赫兹⎯⎯⎯⎯⎯√$0.28\mathrm{K}/\sqrt{\mathrm{Hz}}$$0.28\mathrm{K}/\sqrt{\mathrm{Hz}}$
.块状 NV 自旋特性和增强荧光的结合显著提高了基于 ND 的量子传感器对生物应用的灵敏度。