Homogeneous gold nanoparticle monolayers—QCM and electrokinetic characteristics

Abstract

Deposition mechanism of gold nanoparticles on poly(allylamine chloride) (PAH)-modified silica and mica was investigated by the quartz crystal microbalance (QCM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and streaming potential measurements (SP). The influence of the suspension concentration, ionic strengths and pH was studied. It was shown that the particle deposition was irreversible that enabled to precisely determine the maximum coverage of monolayers. The experimental results were quantitatively interpreted in terms of the random sequential adsorption (RSA) model where the bulk and surface transfer steps were considered in a rigorous way. The results obtained by QCM were exploited as reference data for interpreting the streaming potential (SP) measurements of gold nanoparticle monolayer formation at PAH-modified mica. In these experiments the coverage of particles was determined via SEM and AFM imaging of monolayers. This allowed to quantitatively interpret the zeta potential vs. particle coverage dependencies derived from SP measurements in terms of the general electrokinetic model without using adjustable parameters. In this way, a functional dependence was specified for calculating the nanoparticle coverage in situ. Additionally, by using the SP measurements, thorough electrokinetic characteristics of gold nanoparticle monolayers were acquired. They comprised the dependence of the monolayer zeta potential on ionic strength (for a fixed pH) and the acid-base characteristics of monolayers, derived in pH cycling experiments carried out at fixed ionic strength. It was concluded that these results enable to develop a reproducible method for preparing gold nanoparticle monolayers of controlled coverage and well-characterized electrokinetic properties with potential application as protein adsorption platform.