Surface engineering of ultrasmall metal nanoclusters for biomedical applications

Metal nanoclusters (MNCs) have attracted considerable attention in the fields of catalysis and biomedicine due to their ultrasmall size, unique molecular-like properties, rich surface chemistry, good biocompatibility and stability. This report will introduce the progress in the synthesis and application of MNCs from the following aspects: 1) To address the challenges of size control and unclear growth mechanism of MNCs, a universal synthesis method was designed to regulate the reduction kinetics of the reducing agent, achieving controllable tuning of the size of MNCs and revealing the growth mechanism of MNCs of different sizes. 2) By surface engineering, two types of Pt NCs-based catalysts were developed for hydrogen oxidation reaction (HOR) in alkaline media. Theoretical simulations revealed the decisive role of the surface chemistry of Pt NCs in regulating the adsorption and desorption of *H/*OH/CO and the generation of H2O, endowing them with superior catalytic activity and high stability compared to Pt single atoms and Pt particles. Additionally, this catalyst can exhibit high tolerance to CO by weakening the binding energy of CO intermediates. 3) By modifying the surface of Au NCs with different functional molecules, a series of MNC-based theranostic probes were constructed to achieve NIR-II luminescence imaging guided disease treatment. These works may deepen the understanding of MNCs at the atomic level and promote their application in catalysis and biomedicine.