Facile generation of surface diversity in gold nanoparticles

Surface chemistry is a key determinant of the physico-chemical and biological properties of gold nanoparticles (AuNPs). The introduction of chemical diversity in the surface of AuNPs is usually accomplished by place-exchange reactions using incoming ligands containing the desired terminal functional groups. As an alternative approach, we present here a simple, practical methodology to modify the surface of gold nanoparticles that allows the preparation of AuNPs stabilized with polyethyleneglycol (PEG) ligands with different surface chemistries using AuNPs stabilized with thiol-PEG-amino ligands as starting material. The surface modification reaction involves the acylation of the terminal amino groups in the ligand with an organic acid anhydride in an aqueous buffer. In addition to a full surface modification, this method also allows the synthesis of AuNPs with tailored mixed surfaces, containing two or more different functional groups, each of them at the desired extent. The ease of the experimental conditions for the reaction, purification, and for determining the level of surface modification makes this strategy an attractive alternative to current methods for the preparation of AuNPs with diverse surface chemistry.