Characterization of viscoelastic properties of adsorbed biomolecules and biomolecular assemblies with high frequency micromachined quartz resonators

Micromachined quartz crystal resonator arrays operating in the 66–69 MHz fundamental mode range were tested for their ability to provide high sensitivity to mass loading and viscoelastic properties of biomolecules and biomolecular assemblies. Calibrations using viscous water–glycerol mixtures give the expected linear dependence on the square root of the density–viscosity product. Sequential adsorption of avidin layers interspersed with dithiobis(sulfosuccinimidylpropionate) (DTSSP) or biotynilated bovine albumin (BBA) cross-linker layers provided thick and planar viscoelastic layers for testing. The data reveal a high Q-factor sensitivity and the observed complex impedance changes could be accounted for using a layer dependent, variable viscosity model treated with continuum mechanics approach. The best interpretation of the frequency and Q-factor changes indicates that the layer material properties are most likely dominated by the frictional effects arising from the inter-linking molecules between the layers. These results show the ability of these high frequency micro resonators as an incisive tool for analyzing both static loading and dynamic viscoelastic properties of bimolecular adsorbates.