Hydration shell water surrounding citrate-stabilised gold nanoparticles

Abstract

The presence of foreign particles in an aqueous dispersion perturbs the water layers in the vicinity of the particles. These perturbed water molecules form what is known as the hydration shell and possess different structural attributes from those in the bulk dispersion. Here, Raman spectroscopy was utilised to study such hydration shells around citrate-stabilised gold nanoparticles. An aqueous dilution series of three sizes of gold nanoparticle samples was prepared. The hydration shell spectral response recovered by applying the multivariate curve resolution technique was compared against the spectra of the bulk phase. It could be inferred from the comparison that the hydration shell contains a less extensive hydrogen-bonding network with a smaller number of hydrogen-bonding interactions per molecule being possible than that in bulk. Control experiments and molecular dynamics simulations, using a modified Drude oscillator model for the gold, point to the presence of the gold surface to be the predominant factor behind influencing the hydrogen-bonding structure of the hydration shell water surrounding citrate-stabilised gold nanoparticles.