Thermal and conductivity dependence of GaAs based acoustic biosensors

GaAs BAW sensors using shear acoustic waves were developed for biological detection and quantification. The sensor consists of a 50-350 mu m thick membrane where thickness shear acoustic waves were produced with a lateral field excitation (LFE). The LFE electrode arrangement is located on one side of the membrane. The other side is dedicated for proteins or cells capture through a bio-functionalized interface formed on the GaAs surface. Sensitivity of this type of sensor had been evaluated by modeling to 0.1ng.Hz(-1). Detection needs to be done in liquid environment with complex biological analytes such as blood or plasma. These analytes can inevitably induce temperature and surface charge variations on the material. Therefore, we have examined in the present work, temperature effect and conductivity influence of surrounding substrate or liquid on the GaAs-BAW sensor. These dependences on the resonant frequency are important features when designing GaAs ultrasensitive sensors. Frequency shift of shear mode induced by temperature deviation is reported at -58.6ppm/degrees C. Charge effects were measured by placing the resonant structure onto various bulk materials, thin films or liquids with varying permittivity and conductivity. Overall impedance module decreases when the device is on a highly conductive material, in same way resonant frequencies amplitudes are attenuated. The strong dependence of the sensor response on these parameters overcomes the known dependence on mass or viscosity. These studies give essential elements for the use of GaAs as a sensitive acoustic sensor in biological field.