The kinetics of adsorption of monodisperse nanosized silica particles (32-190 nm diameter) on silicon wafers modified with an aminopropylsilane have been studied by optical reflectometry under stagnant-flow conditions. The adsorption of negatively charged particles on a positively charged wafer surface is driven by electrical double layer attraction and was not found to be measurably reversible. The initial rate of particle adsorption decreases with increasing particle size while the equilibrium amount adsorbed increases with electrolyte concentration. The effect of particle adsorption on the ζ potential of similarly modified glass slides was measured using streaming potential apparatus. The coverage of particles was varied using electrolyte as indicated by the reflectometry measurements. The results suggest that displacement of the plane of shear is not localized to particle covered areas.