Adsorption of anionic gold nanoparticles by a layer of cationic microgel particles deposited on a gold-coated, quartz surface: studied by quartz crystal microbalance and atomic force microscopy

The uptake of gold [Au-MES] nanoparticles by pH-responsive poly(2-vinylpyridine) [P2VP] microgel particles, deposited on a surface, has been studied using a quartz crystal microbalance with dissipation monitoring [QCM-D]. QCM-D, which has not previously been applied to such systems, has been shown to be a promising technique for their analysis, especially when combined with a complementary technique such as atomic force microscopy [AFM]. The QCM-D technique, which provides information on mass and viscosity changes of material adsorbed to a surface, has been used to follow the adsorption of microgel particles to a surface, their subsequent swelling and collapse due to changing the system pH, and the uptake of Au-MES nanoparticles by the P2VP particles. Microgel particles with differing cross-linker content have been compared, following uptake by microgel particles in both their collapsed and swollen states. Qualitative differences in the QCM-D response were observed between microgels with differing cross-linker content (and hence different swelling properties). It was shown that uptake of Au-MES nanoparticles acted to fully and irreversibly collapse the swollen P2VP microgels, inhibiting their pH response. The Sauerbrey relationship was used to equate frequency changes measured by QCM-D to mass allowing sorption amounts for the uptake of Au-MES nanoparticles by P2VP particles to be obtained for these surface-constrained systems.