The stability of Au nanoparticles (AuNPs) is easily affected by environmental factors, and the use of expensive disposable AuNP-based probes not only wastes resources but also increases the cost of detection. Therefore, there is an urgent need to develop stable and recyclable AuNP-based probes. Here, highly stable AuNPs were synthesized via an in situ reduction reaction between HAuCl₄ and hyperbranched polyethylenimine (HPEI). We used HPEI to replace the small molecule reducing agent as a green reducer and template for the green and facile preparation of AuNPs as well as a good stabilizer and decorator of AuNPs. Due to the good properties (massive amount of amino groups, excellent reduction ability and hyperbranched topology structure) of HPEI, the HPEI–AuNPs are highly stable under high temperatures, strong ionic strength and different pH conditions. Meanwhile, the reductive HPEI was also used as the reducing agent to reduce Ag⁺ to Ag⁰; this can combine with AuNPs to form stable Au–Ag core–shell NPs accompanied by a special red-to-brown color change, achieving the colorimetric detection of Ag⁺ by the naked eye. Moreover, this HPEI–AuNP probe not only exhibits good selectivity and high sensitivity (a LOD of 0.41 μM) towards Ag⁺ but has also been successfully applied in real water samples (drinking and tap water). More importantly, by taking advantage of an etching reaction of the Ag shell of the Au–Ag core–shell NPs, a recoverable and reusable HPEI–AuNP probe towards Ag⁺ was developed successfully. This novel colorimetric system shows excellent recyclability and reusability, which is inspirational for the development of low-cost AuNP colorimetric probes and consistent with the idea of green chemistry.

中文翻译：

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可循环使用的比色探针：用于选择性Ag +检测的原位制备高度稳定的HPEI–AuNPs

Au纳米颗粒（AuNPs）的稳定性容易受到环境因素的影响，使用昂贵的基于AuNP的一次性抛弃探针不仅浪费资源，而且增加了检测成本。因此，迫切需要开发稳定且可回收的基于AuNP的探针。在这里，通过HAuCl ₄之间的原位还原反应合成了高度稳定的AuNP和超支化聚乙烯亚胺（HPEI）。我们使用HPEI代替小分子还原剂，将其作为绿色还原剂和模板，用于绿色，简便地制备AuNPs，以及良好的AuNPs稳定剂和装饰剂。由于HPEI的良好特性（大量的氨基，出色的还原能力和超支化的拓扑结构），HPEI–AuNP在高温，强离子强度和不同pH条件下都非常稳定。同时，还使用还原性HPEI作为还原剂将Ag ⁺还原为Ag ⁰。它可以与AuNPs结合形成稳定的Au–Ag核－壳NPs，并伴随特殊的红棕色变化，从而实现Ag ⁺的比色检测用肉眼 而且，这种HPEI–AuNP探针不仅对银⁺表现出良好的选择性和高灵敏度（0.41μM的LOD），而且已成功应用于真实水样（饮用水和自来水）中。更重要的是，通过利用Au-Ag核-壳NP的Ag壳的刻蚀反应，成功开发了可回收和可重复使用的针对Ag ^+的HPEI-AuNP探针。这种新颖的比色系统显示出出色的可回收性和可重复使用性，这对于开发低成本AuNP比色探针具有启发性，并且与绿色化学的思想相一致。