Boron-doped graphitic carbon nitride quantum dots (B-gC₃N₄ QDs) are synthesized through a simple thermal process and functionalized with l-Cysteine (l-Cys) via an EDC/NHS coupling reaction. The resulting l-Cys/B-gC₃N₄ QDs demonstrate a high quantum yield of 28%, excellent water solubility, and resistance to photobleaching and ionic strength. These quantum dots are employed as fluorescent probes for detecting Cd²⁺ ions at trace levels in water. They exhibit a fluorescence signal enhancement in response to Cd²⁺ ions, attributed to a chelation-enhanced fluorescence (CHEF) mechanism. The sensor detects Cd²⁺ ions within a linear range of 0.1–0.7 μM, with a detection limit of 0.23 μM and a binding constant of 9.83 × 10⁵ M^–1. Cytotoxicity assays reveal that l-Cys/B-gC₃N₄ QDs, both alone and in the presence of Cd²⁺, show no DNA damage or cell membrane disruption, confirming their nontoxic nature. Furthermore, the sensor achieves high accuracy in detecting Cd²⁺ in real water samples, with recovery rates ranging from 95 to 106%. This work presents a sustainable, biocompatible, and cost-effective fluorescent probe for real-time monitoring of cadmium ions in environmental water sources.

中文翻译：

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L-半胱氨酸官能化硼掺杂石墨氮化碳量子点：一种用于水中镉检测的生物相容性荧光传感器


硼掺杂石墨氮化碳量子点 （B-gC，₃，_{N， 4} QDs） 通过简单的热过程合成，并通过 EDC/NHS 偶联反应用 l-半胱氨酸 （l-Cys） 官能化。所得的 l-Cys/B-gC₃N₄ 量子点表现出 28% 的高量子产率、优异的水溶性以及耐光漂白性和离子强度。这些量子点用作荧光探针，用于检测水中痕量水平的 Cd²⁺ 离子。它们在 Cd²⁺ 离子的响应下表现出荧光信号增强，这归因于螯合增强荧光 （CHEF） 机制。该传感器可在 0.1–0.7 μM 的线性范围内检测 Cd²⁺ 离子，检测限为 0.23 μM，结合常数为 9.83 × 10⁵ M^–1。细胞毒性测定显示，l-Cys/B-gC₃N₄ QDs，无论是单独使用还是在 Cd²⁺ 存在下，均未显示 DNA 损伤或细胞膜破坏，证实了其无毒性质。此外，该传感器在检测实际水样中的 Cd²⁺ 时实现了很高的准确度，回收率从 95% 到 106% 不等。这项工作提出了一种可持续的、生物相容性的、具有成本效益的荧光探针，用于实时监测环境水源中的镉离子。