Luminescent noble metal nanoclusters as an emerging optical probe for sensor development

In the past few years, highly luminescent noble metal nanoclusters (e.g., Au and Ag NCs or Au/Ag NCs in short) have emerged as a class of promising optical probes for the construction of high-performance optical sensors because of their ultrasmall size (<2 nm), strong luminescence, good photostability, excellent biocompatibility, and unique metal-core@ligand-shell structure. In this Focus Review, we briefly summarize the common syntheses for water-soluble highly-luminescent thiolate- and protein-protected Au/Ag NCs and their interesting luminescence properties, highlight recent progress in their use as optical sensors with an emphasis on the mechanisms underlying their selectivity, and finally discuss approaches to improving their sensitivity. The scope of the works surveyed is confined to highly luminescent thiolate- and protein-protected Au/Ag NCs.