We report Brownian motions of colloidal silica particles (diameter: 325 nm) modified with polyacrylamide (PAAm), near the surfaces of PAAm-modified glass. Aqueous solutions of ethanol (EtOH) are used as the dispersion media, and the solvent properties with respect to PAAm chains are tuned by varying the EtOH concentrations. The mean-square displacements, sigma(2), of the individual particles are determined from particle trajectories obtained by optical microscopy. The diffusion coefficients of the particles, determined from the slopes of sigma(2)-t plots, are smaller at higher EtOH concentrations as a result of increases in the magnitude of interactions between the PAAm chains on the colloidal particles and those on the glass surfaces.