A dual-frequency QCM-D setup operating at elevated oscillation amplitudes.

An often raised, but rarely addressed, question with respect to applications of the quartz crystal microbalance technique is whether the shear oscillation of the sensor surface influences the adsorption kinetics or binding events being studied. Motivated by this uncertainty, as well as by the possibility of using elevated amplitudes to influence and steer specific biomolecular interactions, we have further developed the quartz crystal microbalance with dissipation monitoring (QCM-D) technique to operate in dual-frequency mode. One mode (one harmonic) is utilized for continuous excitation of the QCM-D sensor at resonance, at variable driving amplitudes, while the other mode (another harmonic) is used for combined frequency and energy dissipation (damping) measurements. To evaluate this experimental approach, we investigated the following: (i) the well-established process by which intact lipid vesicles adsorb and decompose into a planar supported lipid bilayer on SiO2, recently shown to be very sensitive to external perturbations, and (ii) specific streptavidin binding to biotin-modified surfaces. In the former case, we observed a clear influence of elevated oscillation amplitudes on the bilayer formation kinetics, while in the latter case, no influence was observed for protein monomers. However, binding was inhibited when the biotin-binding protein was coupled to colloidal particles (o.d. approximately 200 nm).