Control of Colloidal Interactions to Form Biodegradable Gold Nanoparticle Clusters with High-NIR Absorbance
There is significant interest in designing metal nanoparticle agents for biomedical imaging which can be efficiently cleared from the body. Herein, we tune the formation of gold nanoclusters from 5 nm primary gold nanospheres by manipulating the colloidal interaction to control nucleation, growth and passivation. The nanoclusters of closely spaced primary particles exhibit high near-infrared (NIR) absorbance as a consequence of the short stabilizing ligands on the particle surface. In acidic environments in endosomes, the nanoclusters have the capability to fully dissociate back to primary particles, which would enable efficient renal clearance. The kinetic aspects of nanocluster formation are manipulated via controlling colloidal interactions, concentration pathways, and quenching with a weakly adsorbed polymer stabilizer. The charge on the primary ~5 nm citrate-coated gold nanospheres is tailored through place exchange reactions with a variety of biocompatible ligands including positively charged lysine and neutral cysteine. Shortly after initiation of nanocluster growth, a biodegradable polymer, PLA(1k)-b-PEG(10k)-b-PLA(1k) is used to quench the particle growth and provide colloidal stabilization, as characterized with TEM and dynamic light scattering. This work is contrasted with earlier studies where the growth was controlled via solvent evaporation.