Detection of protein binding by shear mode ultrasonic reflection coefficients using c-axis tilted ScAlN film above 100MHz

QCM (quartz crystal microbalance) is suitable for biomolecules sensing since AT-cut quartz operates in shear mode. However, it is not clear that whether the decrease of resonant frequency due to protein-binding on the on the resonator surface is caused by mass loading or viscoelastic change near the surface. The ultrasonic reflectometry is one of the ways to determine viscoelastic properties of liquids such as the complex acoustic impedance, the shear modulus, and the shear viscosity. These properties can be determined from the shear wave complex reflection coefficient at the solid - liquid boundary. In this study, we investigated the shear wave reflection change due to biotin-streptavidin interaction using quasi shear mode c-axis tilted ScAlN thin film. As a result, the change of amplitude and phase of shear reflection coefficient were qualitatively observed when 200 µg/ml streptavidin were introduced to the biotin-coated self-assembled monolayers (SAMs) on the reflection boundary.