Monitoring cell adhesion by piezoresonators: impact of increasing oscillation amplitudes

In recent years, the quartz crystal microbalance (QCM) has been established as a sensitive analytical tool to monitor the attachment and spreading of mammalian cells to in vitro surfaces. Due to its superior time resolution, the device is capable of reading even subtle differences in cell adhesion kinetics. However, thickness shear mode piezoresonators, which are the core component of the QCM approach, can be used not only as a sensor but also as an actuator when the oscillation amplitude of the crystal is increased so that molecular recognition at the solid-liquid interface is disturbed. In this study, we have addressed the impact of elevated lateral oscillation amplitudes on the adhesion kinetics of three mammalian cell lines. We used AT-cut piezoresonators with a fundamental resonance frequency of 5 MHz, and the analytical readout was performed by impedance analysis. Formation of stable cell-substrate contacts is retarded or entirely blocked when the lateral oscillation amplitude (in the center of the resonator) exceeds values higher than 20 nm. Shear oscillations of similar amplitude were, however, not sufficient to displace attached cells from the surface. Moreover, the experimental data prove that the normal QCM readout with oscillation amplitudes smaller than 1 nm is, indeed, non-invasive with respect to mammalian cells.