Exploring Nanoscale Biology With Chip-Scale Surface and Bulk Ultrasonic Wave Sensors

Biological sensors require high sensitivity, specificity, and low limits of detection. Among the most effective sensing modalities are resonators, which employ sensitive resonance and phase change detection techniques. This review article will discuss the design and use of ultrasonic resonators for biological applications. By functionalizing the device substrate surface, resonators can demonstrate high specificity for a biological target of interest. The sensing capabilities of these resonators can be further optimized through design modifications, such as increasing the resonance frequency, improving the quality factor or altering the device configuration. This review article focuses on the two major categories of ultrasonic resonators used as sensors: bulk acoustic wave (BAW) resonators and surface acoustic wave (SAW) resonators. These devices can be further classified based on the excited wave mode, the device layout, and the functionalized layer configuration. Conceptually, these are hybrid pieces of nanotechnology, comprising of chip-scale resonators physically interfaced with functionalized nanofilms that bind biological targets. This review aims to structure the classification of acoustic resonators for biological sensing and compare the most common categories of chip-scale ultrasonic resonators by outlining the advantages and disadvantages for each wave mode and configuration. This comparison will help deduce the optimal design for various biological sensing applications, ultimately supporting the development of more effective biological and biomedical sensors using chip-scale ultrasonics.