Effects of ligand-receptor geometry and stoichiometry on protein-induced aggregation of biotin-modified colloidal gold

Colloidal gold nanoparticles have been modified with a biotin analogue (DSDA). On addition of streptavidin, a biotin-binding protein, nanoparticle aggregation is observed. The extent and rate of aggregation depend on the relative concentrations of gold nanoparticles, DSDA, and streptavidin. To explain these effects, a model has been developed. This model is an extension of both the classical Smoluchowski model of aggregation and the recently developed model of linker induced aggregation (Kisak et al.). The inclusion of geometric and steric factors in our model explains several features that are relevant with our gold particles. The essential differences between our system and that of Kisak et al, are discussed as well as possible future areas of study.