pH Dependent Change in the Optical Properties of Surface Modified Gold Nanoparticles Using Bovine Serum Albumin

The effect of coatings of Bovine Serum Albumin (BSA) on the optical properties and reactivity of surface- modified gold nanoparticles in different pH buffer solutions is presented. Aggregation of uncoated gold nanoparticles is seen in all pH buffer solutions. The presence of these aggregations is observed in the absorption spectra by the appearance of a second, red-shifting peak in the spectra and is confirmed in transmission electron micrographs. Coating of individual gold nanoparticles with BSA prevents the aggregation of nanoparticles in solutions with a pH greater than 5. It is concluded, based upon analysis of visible absorption spectra of the coated and uncoated gold nanoparticles, that the BSA coating on the gold nanoparticles also causes a decrease in the scattering of light in lower pH buffe r solutions. Analysis of Mie’s theory on the optical extinction of light by metal particles supports the interpretation of the spectra