Integration of Surface Acoustic Wave and Microfluidic Technologies for Liquid-Phase Sensing Applications

Sammanfattning: This thesis discusses a new concept for construction of a novel SAW in-liquid sensor employing surface acoustic wave resonance (SAR) in a one-port configuration. In this concept, the reflective gratings of a one-port SAW resonator are employed as mass loading-sensing elements, while the SAW transducer is protected from the measurement environment, reducing power losses significantly. Microfluidic technologies have developed during the last decades into versatile platforms for miniaturized analytical devices. The devices are small, low cost, capable of multi-step automation resulting in fast turnaround, and allow reducing the amount of reagent and sample consumption, while maintaining a precise control over the environment. In this context, small, cheap and efficient sensors capable of in-liquid operation within microfluidic devices are in a great demand. The introduction of acoustic wave technology onto lab-on-a-chip platforms provides sensing capability that meets these criteria, and allows for an extended set of functions to be implemented, e.g., fast fluidic actuation, contact-free particle manipulation, sorting, and others. A resonant SAW sensor topology embedded in a polydimethylsiloxane (PDMS) microfluidic analyte delivery system was fabricated and characterized. Designs with the best performance were identified, and initial measurements in a liquid environment are discussed. In comparison to a delay-line topology, the proposed one-port resonant configuration features improved sensitivity, while offering better electrical performance and smaller size, which allows for wafer-scale fabrication and facilitates integration. Following optimization, sensing performance was evaluated by means of different assays, and multiparametric sensing was demonstrated by sharing of sensor components for simultaneous SAR sensing and electrochemical impedance spectroscopy in different frequency bands. This technological advancement may open pathways to new analytical instrumentation. The small sensor footprint, low energy consumption, and simple two-wire readout facilitate the integration in hand-held “lab on a chip” assay devices, the construction of sensing arrays for parallel sample processing, and the implementation of wireless data transfer schemes.