Microbalance sensor applications using the piezoelectric crystal material GaPO4

Gallium phosphate, GaPO₄, is a piezoelectric crystal material homeotypic to quartz which features outstanding thermal stability up to 970degC, higher coupling than quartz and good temperature compensation for resonant applications. We report results in the research and development for high- temperature micro balance including thermo gravimetric analysis and for affinity sensor applications in aqueous liquids, such as biosensors. A sensor head for high-temperature micro balance applications with an integrated heater was developed. The clamping and heating device for the GaPO₄ resonator was designed for mechanical stability, reliable contacting and homogeneous temperature distribution. Cycles up to 600degC allow separation of volatile and fixed parts of layers deposited on the resonator surface and pyrolytic cleaning from carbonaceous residues. Another interesting field is the application of GaPO₄ for affinity measurements in liquids, e.g. for biosensors. An optimized crystal cut was developed and tested which allows temperature compensation in contact with an aqueous solution. A flow cell with a design for better reproducibility was constructed.