Water contamination by copper ions (Cu²⁺) and sulfide anions (S^2-) has been a longstanding human health hazard. The limitations of current detection strategies have created a high demand for effectively monitoring the concentrations of these ions in water systems. A facile fluorescent bioassay for Cu²⁺ and S^2- was developed in this study based on “on-off-on” fluorescent nitrogen-doped carbon dots (N-CDs). N-CDs were synthesized for the first time via thermal treatment using hexamethylene-tetramine and ammonium citrate precursors. The obtained CDs were highly stable in aqueous solution, with a strong green emission and a 51.2% quantum yield. The maximum fluorescence emission peak was observed at 478 nm for a 360-nm excitation. Notably, the fluorescence intensity of N-CDs can be quenched by a factor of 6 by Cu²⁺, which can be applied to Cu²⁺ assays ranging from 0.05 to 5 μM with a limit of detection (LOD) of 25 nM. Interestingly, further addition of S^2- recovered the fluorescence of the N-CD@Cu²⁺ nanocomplex, which can be used to quantify S^2- in a broad range from 0.05 to 10 μM with an LOD of 32 nM. The N-CD and N-CD@Cu²⁺ nanocomplexes were also demonstrated to be highly specific towards Cu²⁺ and S^2-, respectively. Finally, the sensor was successfully applied to lake water for detecting both Cu²⁺ and S^2-, demonstrating excellent application prospects for analytical chemistry and environmental remediation.

铜离子（Cu ²⁺）和硫化物阴离子（S ^2-）对水的污染一直是对人类健康的长期危害。当前检测策略的局限性对有效监控水系统中这些离子的浓度提出了很高的要求。Cu ²⁺和S ^2-的简便荧光生物测定在这项研究中基于“开-关-开”荧光氮掺杂碳点（N-CD）开发了碳纳米管。通过使用六亚甲基四胺和柠檬酸铵前体进行热处理，首次合成了N-CD。所获得的CD在水溶液中高度稳定，具有强烈的绿色发射和51.2％的量子产率。对于360 nm激发，在478 nm处观察到最大荧光发射峰。值得注意的是，N-CDs的荧光强度可通过Cu ²⁺淬灭6倍，可将其应用于范围从0.05到5μM的Cu ²⁺检测，检测限（LOD）为25 nM。有趣的是，进一步添加S ^2-可恢复N-CD @ Cu ²⁺纳米复合物的荧光，可用于定量S^2-的范围从0.05到10μM，LOD为32 nM。N-CD和N-CD @ Cu ²⁺纳米复合物也分别对Cu ²⁺和S ^2-具有高度特异性。最终，该传感器成功应用于湖水中，可同时检测Cu ²⁺和S ^2-，在分析化学和环境修复方面具有很好的应用前景。