Customizable Ligand Exchange for Tailored Surface Property of Noble Metal Nanocrystals

It is highly desirable, while still challenging, to obtain noble metal nanocrystals with custom capping ligands, because their colloidal synthesis relies on specific capping ligands for the shape control while conventional ligand exchange processes suffer from "the strong replaces the weak" limitation, which greatly hinders their applications. Herein, we report a general and effective ligand exchange approach that can replace the native capping ligands of noble metal nanocrystals with virtually any type of ligands, producing flexibly tailored surface properties. The key is to use diethylamine with conveniently switchable binding affinity to the metal surface as an intermediate ligand. As a strong ligand, it in its original form can effectively remove the native ligands; while protonated, it loses its binding affinity and facilitates the adsorption of new ligands, especially weak ones, onto the metal surface. By this means, the irreversible order in the conventional ligand exchange processes could be overcome. The efficacy of the strategy is demonstrated by mutual exchange of the capping ligands among cetyltrimethylammonium, citrate, polyvinylpyrrolidone, and oleylamine. This novel strategy significantly expands our ability to manipulate the surface property of noble metal nanocrystals and extends their applicability to a wide range of fields, particularly biomedical applications.