In the present work, we use β-casein as a model protein to prepare a smart β-casein stabilized Pt nanoparticle (CM–PtNP) with peroxidase mimicking activity and systematically investigate sulfide-mediated switching effect and mechanism of CM–PtNP nanozyme’s activity. Sulfide-mediated activity switching effect depends heavily on the physicochemical properties of nanozymes and the identity of substrate. On one hand, the binding of sulfide to a Pt nanozyme surface leads to the transform from Pt²⁺ to Pt⁰, resulting in more active sites and the activity “switching on”; on the other hand, the binding of sulfide ions via Pt–S interaction blocks the active sites, resulting in the activity “switching off”. For substrates 3,3′,5,5′-tetramethylbenzidine and 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt, the two factors play different decisive roles since the interaction of substrate molecules with nanozyme allows their different distributions on nanozyme surfaces. By virtue of this specific response, excellent sulfide colorimetric sensors with different limits of detection were developed based on CM–PtNP with different substrates. This is the first report about a fundamental understanding of how substrates influence the anion-mediated activity switching effect by illuminating the nature of anion–nanozyme interaction and nanozyme–substrate interaction. This may be useful to rationally predict the environment factors on the activities of the nanozyme and to design an effective signal amplification based on target-induced nanozyme deactivation/activation.

中文翻译：

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硫化物离子对蛋白质稳定的铂纳米酶的过氧化物酶模拟活性的转换：底物的依赖性，机理和检测。

在目前的工作中，我们使用β-酪蛋白作为模型蛋白来制备具有过氧化物酶模拟活性的智能β-酪蛋白稳定的Pt纳米颗粒（CM-PtNP），并系统地研究硫化物介导的开关作用和CM-PtNP纳米酶活性的机制。硫化物介导的活性转换效应在很大程度上取决于纳米酶的理化性质和底物的身份。一方面，硫化物与Pt纳米酶表面的结合导致从Pt ²⁺到Pt ⁰的转变，从而导致更多的活动站点和活动“开启”；另一方面，硫化物离子通过Pt–S相互作用的结合会阻断活性位点，导致活性“关闭”。对于底物3,3'，5,5'-四甲基联苯胺和2,2'-叠氮基双（3-乙基苯并噻唑啉-6-磺酸）二铵盐，这两个因素起着不同的决定性作用，因为底物分子与纳米酶的相互作用使得它们在纳米酶表面的不同分布。凭借这种特殊的响应，基于具有不同底物的CM–PtNP，开发了具有不同检测限的出色的硫化物比色传感器。这是第一个关于底物如何通过阐明阴离子-纳米酶相互作用和纳米酶-底物相互作用的性质来影响阴离子介导的活性转换作用的基本理解的报告。这可能有助于合理地预测纳米酶活性的环境因素，并基于靶标诱导的纳米酶失活/激活来设计有效的信号放大。