Design of mutually interacting multi-directional transducer configurations on a surface acoustic wave device for enhanced biosensing

Transducers used in biosensing applications are plagued by biofouling, which refers to the binding of nonspecific proteins to the device surface resulting in a compromise of the device sensitivity and selectivity. Acoustic streaming, resulting from high intensity sound waves, has the potential to address the issue of biofouling elimination in biosensors. Multi-directional transducers have the capability of achieving the dual objectives of biosensing and non-specifically bound protein removal for improved sensor performance. Also, focused interdigital transducers (IDTs) have the potential for acoustic energy focusing, thereby increasing the intensity of acoustic streaming. We have identified that various crystallographic orientation allow the propagation of different modes thereby rendering them suitable for different applications. For example, in Langasite, shear horizontal modes propagate along (0, 22, 90) Euler direction while mixed modes with prominent surface normal component are obtained along (0, 22, 0) direction. Thus, the (0, 22, 90) and (0, 22, 0) directions are suitable for biosensing and is suited for removal of NSB founding proteins from device surface. In this work, we investigate a Langasite based biosensor with a mutually interacting multidirectional IDT configuration along the two identified Euler directions for enhanced biosensor performance. Uniform IDTs (U-IDTs) are employed in the (0, 22, 90) direction while focused IDTs (F-IDTs) are placed along the (0, 22, 0) direction. The enhancement in sensor performance was analyzed in terms of device sensitivity and acoustic streaming force. Our results indicate that the streaming force and the sensitivity for the device with the mutually interacting U-IDTs/F-IDTs are significantly higher when compared to uniform unidirectional IDTs. Thus, the Langasite based device with mutually interaction U-IDTs and F-IDTs represents a significant enhancement over the conventional SAW device having uniform IDTs and is better suited for biosensing 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.