In this study a novel method was developed for the fluorescent and colorimetric determination of cysteine (Cys). The fluorescent determination was designed based on surface plasmon-enhanced energy transfer (SPEET), and phosphorus/nitrogen co-doped CQDs (PNCQDs) were employed as the donor, of which the fluorescence was quenched by gold nanorods (AuNRs) (acceptor). For the colorimetric assay, under the catalytic effect of Fe³⁺, AuNRs were effectively etched by OH· that was generated by the Fenton reaction. The etch of the AuNRs lead to the decrease in the absorbance intensity, the blue shift of longitudinal surface plasmon resonance (LSPR) absorption peak of AuNRs as well as the fluorescence of PNCQDs recovery. However, Cys can suppress this etching reaction by coordination effect between hydrosulfide group (SH) in Cys and Fe³⁺, leading to red shift of the LSPR absorption peak. Similarly, the fluorescence will change with the absorbance. The peak shift and the fluorescence change can be applied to monitor of Cys. Under the optimal operation conditions, highly sensitive determination of Cys was achieved, with the fluorescent detection limit of 1.2 nM and the colorimetric detection limit of 0.9 nM. The linearity of the system towards Cys was in the range of 0.005–25 μM. The highly sensitive determination of Cys in urine samples demonstrates that this method possesses high potential for on-site and visual detection of urine Cys.

在这项研究中，开发了一种用于荧光和比色法测定半胱氨酸（Cys）的新方法。基于表面等离激元增强的能量转移（SPEET）设计了荧光测定方法，并采用了磷/氮共掺杂的CQD（PNCQDs）作为供体，其中的荧光被金纳米棒（AuNRs）（受体）淬灭了。对于比色法，在Fe ³⁺的催化作用下，Fenton反应生成的OH·有效地蚀刻了AuNRs。AuNRs的蚀刻导致吸收强度的降低，AuNRs的纵向表面等离子体激元共振（LSPR）吸收峰的蓝移以及PNCQDs的荧光恢复。但是，Cys可以通过氢硫化物基团（SH）在Cys和Fe ^3+中，导致LSPR吸收峰发生红移。同样，荧光会随着吸光度而变化。峰位移和荧光变化可以应用于Cys的监测。在最佳操作条件下，可以对Cys进行高度灵敏的测定，荧光检测限为1.2 nM，比色检测限为0.9 nM。系统对Cys的线性在0.005–25μM的范围内。尿液样品中Cys的高灵敏度测定表明，该方法具有现场和视觉检测尿液Cys的高潜力。