Signal amplification with multilayer arrangements on chemical quartz-crystal-resonator-sensors

Viscoelastic properties of chemically sensitive coatings can amplify the mass sensitivity of quartz-crystal-microbalance-(QCM)-sensors. We developed a sensor concept which is based on a double layer arrangement. Acoustic amplification and chemical sensitivity are separated. With a proper selection of materials the chemical sensitive layer acts pure gravimetrically while the first layer realizes a constant acoustic amplification of the mass effect. Major sensor design parameters are the shear modulus and the thickness of the first layer. They are sufficiently independent from the design of the chemically active layer. Parallel measurement of the resonant frequency of the quartz crystal and its motional resistance in the equivalent circuit can be exploited to check the acoustic amplification.