Nonradiative interactions between biotin-functionalized gold nanoparticles and fluorophore-labeled antibiotin

The interaction between antibodies and ligand-functionalized nanoparticles were exploited in this work by taking advantage of the strong influence that metallic surfaces have on emission of fluorescence. The surface of colloidal gold nanoparticles was functionalized with biotin moieties embedded in a nonfouling matrix of di(ethylene glycol) groups to minimize nonspecific interactions. Anti-biotin labeled with fluorophore Alexa T 488 bound to these particles via specific biomolecular recognition interactions. Upon binding of the labeled antibody to the biotinylated nanoparticles, an immediate decrease in emission of fluorescence was observed. Competitive dissociation of the antibody from the nanoparticles with soluble biotin produced a recovery in the intensity of emission of fluorescence. For large concentrations of the antibody, emission of fluorescence (corrected for dilution and absorption/scattering effects) appeared to increase to levels higher than the intensity of emission of the unbound antibody. This apparent increase is ascribed to a decreased extinction coefficient produced during aggregation of the nanoparticles by the bivalent antibodies. This scheme could have applications in detection of small molecules or could be used to study the interactions of ligand functionalized nanoparticles and proteins.