Application of unidirectional transducers in acoustic plate mode biosensors

One of the most important issues in acoustic plate mode (APM) sensor design has been the excitation of a single acoustic mode within the APM spectrum. In order to acheive this selective excitation without incurring high triple transit distortions, single phase unidirectional transducers (SPUDT) are employed. Thick aluminum electrodes are used to provide strong mechanical reflections and improve the directivity, hence the phase linearity, of the resulting delay line. A dual delay line oscillator (DDLO) sensor measurement system has been evaluated for the selective detection of double-stranded DNA. The observed frequency shifts indicate an essentially linear, reproducible response to chemically denatured DNA samples up to at least 200 ng/mL. The observed fractional frequency change per unit mass (1/f δF/δm) is -6×10-8 ng-1 of DNA in a 1 mL solution.