Fluorescent carbon dots (CDs) have been identified as potential nanosensors and attracted tremendous research interests in wide areas including anti-counterfeiting, environmental and biological sensing and imaging in considering of the attractive optical properties. In this work, we present a CDs based fluorescent sensor from polyvinylpyrrolidone, citric acid, and methionine as precursors by hydrothermal approach. The selective quantifying of Fe³⁺ and ascorbic acid (AA) are based on the fluorescent on-off-on process, in which the fluorescent quenching is induced by the coordination of the Fe³⁺ on the surface of the CDs, while the fluorescence recovery is mainly attributed to redox reaction between Fe³⁺ and AA, breaking the coordination and bringing the fluorescence back. Inspired by the good water solubility and biocompatibility, significant photostability, superior photobleaching resistance as well as high selectivity, sensitivity, and interference immunity, which are constructed mainly from the N,S-doping and methionine surface functionalization, the CDs have not only been employed as fluorescence ink in multiple anti-counterfeiting printing and confidential document writing or transmitting, but also been developed as promising fluorescence sensors in solution and solid by CDs doped test strips and hydrogels for effectively monitoring and removing of Fe³⁺ and AA in environmental aqueous solution. The CDs have been also implemented as effective diagnostic candidates for imaging and tracking of Fe³⁺ and AA in living cells, accelerating the understanding of their function and importance in related biological processes for the prevention and treatment specific diseases.

荧光碳点（CD）已被认为是潜在的纳米传感器，并因其具有吸引力的光学特性而在防伪、环境和生物传感以及成像等广泛领域引起了巨大的研究兴趣。在这项工作中，我们通过水热法提出了一种基于聚乙烯吡咯烷酮、柠檬酸和蛋氨酸作为前体的碳点荧光传感器。^{Fe 3+}和抗坏血酸（AA）的选择性定量是基于荧光开关过程，其中荧光猝灭是由CD表面Fe ³⁺的配位引起的，而荧光恢复主要归因于Fe ³⁺和AA之间的氧化还原反应，打破了配位并使荧光恢复。主要由N,S掺杂和蛋氨酸表面功能化构成的CDs具有良好的水溶性和生物相容性、显着的光稳定性、优异的抗光漂白性以及高选择性、灵敏度和抗干扰性，其不仅被广泛使用作为多种防伪印刷和机密文件写入或传输中的荧光墨水，还可以通过掺杂CD的测试条和水凝胶开发为溶液和固体中的荧光传感器，用于有效监测和去除环境水溶液中的Fe 3+和^AA。CD 还被用作活细胞中 Fe ³⁺和 AA 成像和跟踪的有效诊断候选者，加速了解它们在预防和治疗特定疾病的相关生物过程中的功能和重要性。