Sensing in liquids with SH plate mode devices

Two-port acoustic wave sensors have been fabricated which utilize shear horizontal (SH) acoustic plate modes (APMs) to probe a solid-liquid interface. These modes are excited and detected by interdigital transducers on thinned ST-quartz plates. The APMs propagate efficiently with liquid contacting the device and allow sensing to be performed on the side of the device opposite the transducers. The mass sensitivity of the APM device enables it to function as a microbalance in a number of sensing applications. A chemical sensor capable of detecting low concentrations of Cu²⁺ ions in solution has been constructed by chemically modifying the device surface with ethylene diamine ligands capable of binding ions from solution. This binding can be reversed by the addition of acid to the solution