Surface acoustic wave sensors for the detection of gases and for biological applications

Abstract

The presence of organic or inorganic chemical species can be detected by their reaction with a suitable reagent. In acoustic sensors where the sensor reagent is immobilized on the device, the associated mass increase is detected by a change of the propagation characteristics of an acoustic wave. Acoustic surface wave (SAW) devices promise an advantage over the commonly used quartz oscillators because of their inherent higher sensitivity associated with their high operating frequency of up to several hundred MHz. Until now SAW devices have not found widespread application, mainly because of handling difficulties associated with the necessity to mount these devices on sockets and to connect them electrically with bonding wires. In this contribution, techniques will be presented to overcome problems associated with the operation of SAW sensors in aggressive liquids or in gases at elevated temperatures. A new type of SAW device has been developed in which no ohmic electrical contacts are required. Instead, electrical connection between the device and the electronic circuitry is achieved by inductive coupling. In this way, operation and preparation of the devices is considerably eased. Data will be presented on immunosensing in buffer solutions, and on gas sensing at temperatures up to 500 °C.