Fabrication and application of noble metal nanoclusters as optical sensors for toxic metal ions

Atomically precise noble metal nanoclusters with ultrasmall physical sizes in the subnanometer range have emerged as a new class of probing fluorophores and have attracted considerable research interest because of their intrinsic physical, chemical, optical, biological, and electrical properties, such as stability, biocompatibility, and molecule-like photoluminescence. In comparison with traditional fluorophores such as organic dyes and quantum dots, noble metal nanoclusters have significant advantages, including low toxicity toward the environment and biological tissues, high stability when exposed to irradiation, and small size, that make them more suitable for biological sensing or biological labeling applications. Several reviews have summarized the fabrication of noble metal nanoclusters, including gold, silver, copper, and bimetallic nanoclusters. However, these reviews focused either on various facile preparation methods or multidisciplinary application areas. Here, we focus on the application of noble metal nanoclusters as optical sensing materials for toxic metal ions, including new synthetic approaches and discussion of the detection mechanism. We briefly summarize the development of metal cation monitoring technology that uses ultrasmall nanoclusters as the sensing probes. We also provide a fresh opinion on research expectations in the field of inorganic nanoscience and nanotechnology Finally, perspectives for future research hot topics are discussed.