Cysteine (Cys) is a crucial amino acid. Developing a method for Cys evaluation and detection is necessary for the diagnosis of various diseases. A variety of sensors use graphene quantum dots (GQDs) for biological compound determination; however, GQDs demonstrate very poor fluorescence quantum yield. Therefore, we doped nitrogen and phosphorus into GQDs to form composite material NP-GQDs with enhanced fluorescence properties. NP-GQDs were characterized by ultraviolet-visible, fluorescence spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Then, we used NP-GQDs as donors and silver nanoparticles (AgNPs) as acceptors to design a fluorescence resonance energy transfer (FRET) system for Cys detection. Optimal conditions for sensing were investigated, and under these conditions our FRET system showed good results in Cys determination. The fluorescence intensity of NP-GQDs was quenched proportionally along with increasing Cys concentration from 0.5 to 4.5 µM and the limit of detection (LOD) was 0.1 µM. In the presence of different amino acids, the FRET system also showed excellent selectivity for the Cys detection.

半胱氨酸 (Cys) 是一种至关重要的氨基酸。开发一种用于 Cys 评估和检测的方法对于诊断各种疾病是必要的。多种传感器使用石墨烯量子点（GQD）进行生物化合物测定；然而，GQD 表现出非常差的荧光量子产率。因此，我们将氮和磷掺杂到 GQD 中以形成具有增强荧光特性的复合材料 NP-GQD。通过紫外-可见光、荧光光谱、透射电子显微镜和 X 射线光电子能谱对 NP-GQD 进行了表征。然后，我们使用 NP-GQDs 作为供体和银纳米粒子 (AgNPs) 作为受体设计用于 Cys 检测的荧光共振能量转移 (FRET) 系统。研究了传感的最佳条件，在这些条件下，我们的 FRET 系统在 Cys 测定中显示出良好的结果。NP-GQDs 的荧光强度随着半胱氨酸浓度从 0.5 到 4.5 µM 的增加而成比例地淬灭，检测限 (LOD) 为 0.1 µM。在存在不同氨基酸的情况下，FRET 系统对 Cys 检测也表现出优异的选择性。