N-Acetylcysteine (NAC) plays an important role in optimizing the protective ability of cells as well as in the treatment of some chronic clinical conditions. Unfortunately, current methods for determining NAC based on fluorescence assay strategies remain poorly investigated. In this study, a new fluorescence method for highly sensitive and selective detection of NAC was developed. The detection method employed the fluorescence (FL) signal of branched polyethylenimine-functionalized carbon dots (PEI-CDs) via an off–on mechanism. The detection system was based on the formation of cupric amine complexes by the reaction of Cu²⁺ ions with surface amino groups on PEI-CDs. The FL of PEI-CDs at 460.0 nm upon exciting at 360.0 nm was quenched as a result of electron transfer between the complexes and PEI-CDs. Upon addition of NAC to Cu²⁺-CD solution, electron transfer occurred from the mercapto group on NAC to Cu²⁺, leading to the formation of Cu⁺ species and the dissociation of cupric amine complexes. As a result, the FL signal of PEI-CDs was turned on since single excited electrons cannot be transferred from PEI-CDs to the cupric amine complexes. The detection limit of this method was 0.56 μM, while the linear response ranged from 5.56 μM to 277.8 μM.

中文翻译：

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支链聚乙烯亚胺官能化的碳点作为N-乙酰半胱氨酸的敏感和选择性荧光探针，通过关闭机制

N-乙酰半胱氨酸（NAC）在优化细胞保护能力以及治疗某些慢性临床疾病中起着重要作用。不幸的是，目前基于荧光测定策略确定NAC的方法仍然研究不足。在这项研究中，开发了一种用于高灵敏度和选择性检测NAC的新荧光方法。该检测方法通过关闭机制利用分支的聚乙烯亚胺官能化碳点（PEI-CD）的荧光（FL）信号。该检测系统基于Cu ²⁺反应形成铜胺配合物PEI-CD上具有表面氨基的离子。由于络合物与PEI-CD之间的电子转移，PEI-CD在360.0 nm激发时在460.0 nm处的FL被猝灭。在将NAC加到Cu ²⁺ -CD溶液中后，电子从NAC上的巯基转移到Cu ²⁺，导致Cu ⁺物种的形成和铜胺络合物的解离。结果，由于单个激发电子不能从PEI-CD转移到铜胺络合物，因此PEI-CD的FL信号被打开。该方法的检出限为0.56μM，线性响应范围为5.56μM至277.8μM。