Electromagnetic excitation of high frequency acoustic shear waves for the study of interfacial biochemical phenomena.

摘要

Excitation of acoustic waves in quartz discs has been instigated by exposing the piezoelectric substrate to the electromagnetic field generated from a nearby spiral coil. It has been argued that an induced fluctuating magnetic produces secondary electric fields that couple with the piezoelectric tensor. A comparison of acoustic resonance envelopes derived in air and under liquid demonstrate that the spurious resonant modes, generated in air, appear to be dampened when the disc is exposed to liquid. At the same time, it also appears that the dielectric properties of the liquid medium, at the device liquid interface, contributes to the overall excitation field. In agreement with previous acoustic measurements, increased viscosity of the overlying liquid dampens the mechanical resonance manifesting itself as a change in frequency coupled with a decrease in resonant amplitude and quality factor. Careful manipulation of a number of instruments settings, including the capacitance, the signal generator output voltage, coaxial cable length, and the level of frequency modulation, allows the application of different harmonics as high as the 75th harmonic; although at this level the resonant envelope begins to break down due to a significant reduction in the acoustic Q value. Using quartz crystals with a higher fundamental frequency allowed the generation, of what I believe to be, the first ever-recorded bulk acoustic wave over one gigahertz.; The application of higher harmonics demonstrated a linear dependence between the applied harmonic with the observed frequency shift. Based on previous results from this lab, it is postulated that higher applied frequencies amplify slip effects between the adsorbed layer and the surface of the transducer. In addition, it is proposed that the slip effects do not occur right on the surface of the transducer, rather at a defined plane within the adsorbed layer. The properties of the material within which the plane resides will determine how the acoustic energy propagates in, and interacts with the deposited material. This opens up the potential to increase the sensitivity of the sensor by tailoring the surface chemistry to enhance expected responses.; The new EM configuration was directly compared to a more conventional acoustic wave sensor, the thickness-shear-mode (TSM). The TSM was operated at the first harmonic (9MHz), whereas the EM device functioned successfully at 453 MHz (47th harmonic). The nature of the signals produced from the two devices are compared based on their respective signal-to-noise rations and relative standard deviations. A compared response of the new EM configuration to the introduction of the protein neutravidin demonstrated a signal-to-noise ratio that was at least seven times higher than the conventional bulk-acoustic wave structure. The two structures were again compared in response to the interaction of the tat protein to a TAR RNA sequence. The new EM configuration again outperformed the conventional device by demonstrating a three-fold increase in sensitivity to the TAR-tat interaction.; The detection limit of the new EM configuration was investigated using increasingly dilute solutions of neutravidin and was found to be between 7.5 and 5 ppm. However, it should be noted that this was the bulk concentration and not the on-surface concentration. In the future, radiolabelling experiments should be used in order to establish the on-surface detection limit of the device.