Investigations on molecular adsorption and surface charge densities at colloidal gold nanoparticle interfaces are important for the development and optimization of applications such as plamon-enhanced molecular sensing, catalysis, and photovoltaics. Second harmonic generation (SHG), using an ultrafast laser pulse at frequency ? to generate light at 2?, is a powerful technique for studying colloidal nanoparticle surfaces. The adsorption isotherm of the dye molecule, malachite green, adsorbing to gold nanoparticles in solution is measured using SHG to obtain the adsorbate site density and the free energy of adsorption. The surface charge density of colloidal gold nanoparticles is determined using SHG under varying salt concentrations. The results show excellent agreement with the modified Langmuir isotherm and the modified Gouy-Chapman models, and indicate that a Stern layer of adsorbed ions, image-charge attractions, and the nanoparticle surface curvature are all important considerations for a complete understanding of the colloidal gold nanoparticle surface.

Molecular adsorption and surface charge density of colloidal gold nanoparticles studied with second harmonic generation

245th National Meeting (2013)

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