Optically-active nanocrystals (such as quantum dots and plasmonic noble metal nanoparticles) have received great attention due to their size-tunable optical properties. The indicator displacement assay (IDA) with optically-active nanocrystals has become a common practice for optical sensor development, since no sophisticated surface functionalization of nanoparticles is required. Among the IDA-based optical sensors, the use of metal ions as receptors seems to be attractive. Therefore, in this review, the research progress of optical sensing at the nanobiointerface of metal ion–optically-active nanocrystals has been summarized. In particular, metal ion-mediated selective recognition has been summarized here based on the classical Hard–Soft-Acid–Base (HSAB) principle, which has been seldom mentioned before. Most of the references were therefore categorized according to their located place based on the HSAB theory. Besides, several metal ion modulation strategies that were not related to the HSAB theory (e.g., redox modulation) were also included. Finally, due to the cross-talk of metal ions in selective recognition, we have also summarized sensor array development based on multiple metal ion receptors in IDA sensing with optically-active nanocrystals. Several interesting applications of the IDA sensing with metal ions as receptors and optically-active nanocrystals as indicators are presented, with specific emphasis on the design principles and photophysical mechanisms of these probes.

中文翻译：

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金属离子光学活性纳米晶体的纳米生物界面处的光学传感

光学活性纳米晶体（例如量子点和等离激元贵金属纳米颗粒）由于其尺寸可调的光学特性而受到了广泛的关注。具有光学活性纳米晶体的指示剂位移分析（IDA）已成为光学传感器开发的一种常见实践，因为不需要对纳米粒子进行复杂的表面功能化。在基于IDA的光学传感器中，使用金属离子作为受体似乎很有吸引力。因此，在这篇综述中，总结了在金属离子光学活性纳米晶体的纳米生物界面上光学传感的研究进展。特别是，这里基于经典的硬-软-酸-碱（HSAB）原理总结了金属离子介导的选择性识别，该原理以前很少提及。因此，大多数参考文献是根据HSAB理论根据其所处位置进行分类的。此外，几种与HSAB理论无关的金属离子调制策略（例如，氧化还原调制）也包括在内。最后，由于选择性识别中金属离子的串扰，我们还总结了在具有光学活性纳米晶体的IDA传感中基于多种金属离子受体的传感器阵列开发。介绍了IDA传感的一些有趣应用，其中金属离子作为受体，光学活性纳米晶体作为指示剂，特别强调了这些探针的设计原理和光物理机制。