The near-infrared fluorescence of gold nanoclusters stabilized with bovine serum albumin (BSA -AuNCs) centered at 675 nm could be enhanced by cysteine and then effectively quenched by copper ion (Cu²⁺), therefore, cysteine and copper ion could be detected in sequence. At “on” state, fluorescence enhancement of BSA-AuNCs is generated due to the reaction between cysteine and BSA-AuNCs, via filling the surface defect of gold nanoclusters, while Cu²⁺ can further oxidize the reductive sulfydryl of cysteine and interact with amino acids presented in the BSA chain, inducing gold nanoclusters to aggregate, thus causing “off” state with fluorescence quenching. Fluorescence switch of BSA-AuNCs can be used for cysteine and Cu²⁺ detection in mice brain with Alzheimer's disease (AD) in vitro, with fast response, high chemical stability and sensitivity. Besides, it was able to image the endogenous Cu²⁺ in liver and heart of AD mice in situ. The results are promising, especially in the framework of early diagnosis of Alzheimer's disease.

半胱氨酸可增强以675 nm为中心的牛血清白蛋白（BSA -AuNCs）稳定的金纳米团簇的近红外荧光，然后用铜离子（Cu ²⁺）有效地淬灭，因此可检测到半胱氨酸和铜离子顺序。在“开”状态下，由于半胱氨酸与BSA-AuNCs之间的反应，通过填充金纳米团簇的表面缺陷，BSA-AuNCs产生了荧光增强，而Cu ²⁺可以进一步氧化半胱氨酸的还原巯基并与氨基相互作用BSA链中存在的酸，诱导金纳米团簇聚集，从而导致荧光猝灭的“关闭”状态。BSA-AuNCs的荧光开关可用于半胱氨酸和Cu ²⁺在体外检测患有阿尔茨海默氏病（AD）的小鼠大脑，具有快速响应，高化学稳定性和灵敏度。此外，它能够原位成像AD小鼠肝脏和心脏中的内源性Cu ²⁺。该结果是有希望的，特别是在阿尔茨海默氏病的早期诊断框架内。