Kinetics of Noble Metal Nanoparticle Deposition on Silica: Quantitative Interpretation of Quartz Microbalance Results in Terms of the Hydrodynamic Theory

The applicability of the hydrodynamic theory for the interpretation of deposition kinetics of discrete adsorbates with a density much larger than the suspending fluid was assessed. For this purpose, platinum and gold nanoparticles with well-characterized physicochemical properties were used in the experimental investigations. Primarily, the frequency and the bandwidth (dissipation) shifts for various overtones induced by the particle deposition on a silica sensor were acquired as a function of time. These kinetic data were used to determine the imaginary and real components of the sensor impedance scaled by the inertia (Sauerbrey) impedance. The latter was derived from the random sequential adsorption modeling validated by using experimental particle coverage acquired by atomic force microscopy (AFM). In this way, experimental impedance data were determined for various particle sizes, oscillation frequency and ionic strengths. It was confirmed that the experimental results can be adequately interpreted in terms of the hydrodynamic theory, assuming lubricated contact of the particles with the sensor. In contrast, the theoretical results derived for the stiff contact significantly overestimated the experimental data. It was also shown that the imaginary impedance component was weakly dependent on the particle coverage, which enabled quantitative interpretation of the nanoparticle deposition kinetics using the frequency shifts. These results can be used as reference data enhancing the precision of QCM sensing of enzymes and antibodies, where noble metal particle layers are deposited to amplify the signal.