Progress in electrochemistry and electrochemiluminescence of metal clusters

Summary Ultrasmall metal clusters with unique sizes of a few nanometers possess distinct optical, electronic, and magnetic properties different from their nanoparticle counterparts. Over 100 metal clusters with atomically precise designed structures have been reported. In this mini-review, research in the fields of electrochemistry, and electrochemiluminescence (ECL) of metal clusters, has been summarized. Quantized double layer charging voltammetry, or molecule-like voltammetry, could be observed for metal clusters with specific core sizes. These metal clusters always demonstrate rich valence states and can be designed as either electron donors or acceptors; hence, metal clusters are versatile luminophores for ECL. In most cases, the ECL of metal clusters through annihilation routes is very weak, so coreactants are required to enhance the ECL intensity. The mechanisms of these ECL processes can be identified through spooling ECL spectroscopy. This powerful technique yields time-evolved ECL peaks at their corresponding wavelength. The ECL signal could be quenched or amplified by specific biospecies, providing the foundation for ECL applications in biosensors. The thriving development of electrochemistry and ECL of metal clusters provides numerous possibilities for fundamental research and applications.