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pH Dependent Optical Properties of Surface Modified Gold Nanoparticles Using a Bovine Serum Albumin Coating

Y. Xu, K.A. Linares, K. Meehan, B.J. Love and N.G. Love
Virginia Polytechnic Institute and State University, US

Keywords: surface plasmon resonance, gold, nanoparticle, aggregation, bovine serum albumin

Use of gold nanoparticles has significant potential in biosensors. Gold's surface plasmon resonance (SPR) is influenced by the refractive index of the surrounding environment. Changes in the SPR signal can be correlated to changes in the chemical composition of that environment. To study the use of the SPR signal of gold nanoparticles incorporated in live bacteria cells in order to detect changes in the intracellular fluid during a stress response, the tendency of the gold nanoparticles to aggregate must be overcome. Aggregation of uncoated nanoparticles was observed in all solutions (pH 4-8), the range over which the bacteria survive. The presence of these aggregates was observed in the absorption spectra by the appearance of a second, red-shifting peak and confirmed in transmission electron micrographs. Thin coating of bovine serum albumin (BSA) nanoparticles prevented aggregation of gold nanoparticles in solutions with pH > 5. BSA coatings also affected the optical properties of gold nanoparticles. It was concluded, based upon analysis of absorption spectra of the coated and uncoated gold nanoparticles, that the BSA coating on the gold nanoparticles caused a decrease in the scattering of light at lower pH. Analysis of Mei's theory supports the interpretation of the spectra.

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