Ultrasonic plate waves for biochemical measurements

Flexural plate waves can propagate nonradiatively along liquid-immersed plates provided the plate-wave velocity is lower than the speed of sound in the liquid. This low-loss condition has been exploited to measure biochemical processes in liquids. Proteins or other biomolecules that adsorb to the plate surface lower the plate wave velocity, while the viscosity of the liquid causes attenuation of the plate wave. Thin plate-wave structures have been formed with microfabrication techniques. The response of these structures has been experimentally calibrated and found to agree well with theory. The plate-wave delay-line oscillator tested has a mass sensitivity which permits the detection of less than 10 ng of mass adsorbed over the 0.24 cm/sup 2/ membrane area. Fluid viscosities were measured in the range of zero to 10.6 poise. The plate-wave delay-line oscillator frequency was monitored to study the adsorption of protein onto the sensor surface in real time. Plate-wave attenuation was seen to rise sharply over time as a drop of blood on the sensor coagulated.<
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