Mass response of the thickness-shear mode acoustic wave sensor in liquids as a central misleading dogma

Attempts are often made to correlate a shift in series resonant frequency of an oscillating AT-cut device with mass added or removed from the surface of the acoustic wave sensor. For sensors operated in the liquid phase, despite the fact that energy is propagated into the liquid medium, the literature in this field displays a marked tendency to force-fit the Sauerbrey model to experimental results. In reality, the series resonant frequency is governed by a complex array of factors such as interfacial free energy, molecular slip, surface stress and rugosity as well as acousto-electric effects. An unfortunate consequence of the tendency of this adherence to the mass response model is that the extremely exciting promise offered by the acoustic wave sensor, operated in whatever mode, particularly in the study of biological macromolecules, has remained largely unrecognized. Indeed, there is a wide spread belief that the transverse shear mode (TSM) device, for example, is very "insensitive" compared to optical-based devices. The present paper will precis a new model which describes acoustic energy propagation into liquids surrounding the TSM device.