Protein-protected gold/silver alloy nanoclusters in metal-enhanced singlet oxygen generation and their correlation with photoluminescence

摘要

Photoluminescent noble metal nanoclusters (NCs, core size < 2 nm) have recently emerged as a new type of photosensitizers advantageous over conventional photosensitizers due to their high singlet oxygen (O-1(2)) generation efficiency, excellent photostability and water solubility, as well as good biocompatibility for photodynamic therapy and bioimaging. However, no correlation has been established between the intrinsic O-1(2) generation and photoluminescence properties of metal NCs with their size, composition, and concentration, which is important to customize the molecule-like properties of NCs for different applications. Herein, we report a systematic study to uncover the rational design of bimetallic NCs with controllable O-1(2) generation efficiency by tuning their compositions through spontaneous galvanic displacement reaction. A series of ultrasmall gold/silver alloy nanoclusters (AuAgNCs) were synthesized by reacting bovine serum albumin (BSA) protein-protected Ag13NCs (13 Ag atoms/cluster) with varying concentrations of gold precursor at room temperature. It was found that the O-1(2) generation efficiency of the resultant BSA-protected AuAgNCs were inversely correlated to their photoluminescence intensity. Interestingly, plasmonic gold nanoparticles (> 10 nm) were also formed simultaneously by photobleaching of the BSA-AuAgNCs, leading to significant metal enhancement effect to the O-1(2) generation rate much higher (similar to 45 times) than that of the monometallic BSA-Ag13NC. This versatile two-for-one strategy to develop next generation metal-enhanced bimetallic NC photosensitizers in one pot opens up new opportunities in designing advanced hybrid nanomaterials with complementary and/or enhanced functionalities.