Thickness shear mode acoustic wave sensors for characterizing the viscoelastic properties of cell monolayer

The thickness shear mode (TSM) quartz crystal resonator attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface in real time. In this study, a multilayer acoustic wave sensor model including a quartz resonator substrate, a cell-substrate interfacial layer and a cell layer has been developed based on the state of cell adhesion to the quartz resonator substrate. In order to obtain comprehensive and detailed information on the resonator oscillation, the electrical admittance spectrum of the resonator sensor over a range of frequencies near resonance is measured by an impedance analyzer instead of only measuring the resonance frequency and motional resistance with an oscillator circuit. After cells are fully spread to form a monolayer on the surface, the admittance spectrum of the multilayer loaded acoustic wave sensor was recorded and used to extract the viscoelastic properties of the cell layer by fitting experimental spectrum curve with those obtained from the theoretical model through a curve-fitting algorithm. It is found that the viscoelastic properties of the cell layer are consistent with those measured by other techniques, indicating the quartz acoustic wave sensor can be used as a non-invasive device for characterizing the mechanical properties of cell layers.