A novel three dimensional fluid-structure interaction finite element model of wave propagation in SAW device: Application to biosensing & microfluidics

The key issues related to biosensor technology include selectivity, sensitivity, response and recovery times, and detection limit; most of these limitations stem from biofouling resulting from the binding of undesirable moieties such as non-specific proteins to the sensor surface. Thus, removal of non-specifically bound (NSB) proteins remains a significant challenge in biosensing applications. Operation of biosensors in liquid media necessitates an investigation of the fluid-device interaction to understand the mechanisms of biofouling elimination. In this study, we report for the first time, a fully coupled three dimensional transient finite element fluid-solid interaction (FSI) model of the SAW device subject to liquid loading to investigate the streaming velocity fields and forces induced by SAW device. Our simulation results suggest that the SAW-fluid interaction creates a pressure gradient in the direction of acoustic wave propagation in the fluid, leading to an acoustically driven streaming phenomenon known as SAW streaming which can be used for removal of non-specifically bound (NSB) proteins. Computed velocity fields indicate that the normal component of fluid velocity is smaller than the tangential component along the propagation direction. Thus, the SAW induced drag force, arising from the tangential component of fluid velocity and leading to particle advection is an important mechanism in biofouling removal from the SAW device surface and the normal component would prevent the reattachment of the particles to the device surface. Apart from microfluidic applications, this work broadly applies to all transducers used for biological species sensing that suffer from fouling and non-specific binding of protein molecules to the device surface.