Characterization of Protein Using Two-Port STW Resonators

Abstract

A surface acoustic wave (SAW) is an acoustic, mechanical wave that propagates on the surface of a piezoelectric crystal. Coupling to any medium that interacts the surface strongly affects the velocity and amplitude of the wave. In a typical surface transversal wave (STW) resonator, an electrical signal is converted at interdigital transducers (IDT’s) into polarized transversal waves travelling parallel to the sensing surface, utilizing the piezoelectric properties of the substrate material. This approach is very sensitive to biological interactions on the sensor surface. Typically, the wave transmitted is confined to the surface of the substrate. Thus, the acoustic energy is concentrated within the guiding layer rather than in the bulk of the piezoelectric material. The sensitivity of the sensor for surface modifications is increased, by the choice of material, and the design of the guiding layer as well as by the structure of the sensor and the transducers. The output signals are transformed in terms of their frequency or phase with respect to the input signals, due to the interaction of the input signal with the fluid contacting the sensitive surface. Surface acoustic wave (SAW) devices hold a promise in providing ultra fast sensing platform. Research focus is on studying methods to characterize conductance, susceptance, viscosity, and other properties of protein samples, like albumin using Two-Port Surface Transverse Wave (STW) resonator devices quickly and inexpensively using nano-liter volume. When a mass is deposited on the electrode the resultant decrease in resonant frequency can detect mass changes at nanogram level. We propose to advance the sensitivity of the characterization by use of quartz Two-Port STW resonator since they can operate at much higher frequency than bulk wave oscillators.