Analysis of the Nature of Oxyanion Adsorption on Gold Nanomaterial Surfaces

Colloidal gold nanoparticles can be isolated from excess citric acid buffer by electrolyte-induced precipitation from water solutions through the addition of oxyanions. This allows the nanomaterials to be isolated as freely soluble powders that can be readily redissolved in water or buffer solution for other applications, such as biolabeling. Analysis by UV−vis and FTIR spectroscopy allows direct analysis of the oxyanion interaction at the surface of the Au nanomaterial. For a series of oxyanions, the order of thermodynamic stability is CO32- < H2PO41- < SO42, while the shift in the SPR band follows the trend H2PO41- > CO32- > SO42-. These studies indicate that the thermodynamic stability and nature of binding are dictated by the availability of d-orbitals for back-bonding, while the surface plasmon resonance (SPR) band frequency is largely modulated by the electrostatics of the ligand. Comparison of the extinction coefficient of the SPR band to Mie theory predictions further illustrates the effect of ligand interactions on the properties of the Au nanomaterials. Overall, this method produces gold colloidal nanoparticles with labile surface-stabilizing groups that maintain the integrity of the shape and size distribution of the original colloidal gold.