Detection of biomolecules from fluid samples using both qualitative and quantitative assays is essential for patient diagnosis, disease monitoring, and public health surveillance, among other applications. Numerous factors impact assay performance, workflow requirements, and potential end-use cases. These factors include the target biomolecule type, the type of matrix from which the biomolecule is to be detected, and the type of biorecognition elements that can interact with the target. Many qualitative assays benefit from user-friendliness, minimal points of error, and simple signal readouts that eliminate the need for complex instrumentation; however, they often fail to detect rare biomolecules. Moreover, while convenient for rapid testing, they typically cannot yield quantitative results, which lessens their usefulness in some areas. Quantitative assays, however, have the capacity to provide numerical readouts that offer a more comprehensive understanding of patient conditions. However, such assays commonly have multiple potential points of user-related error that can lead to false results; moreover, they often necessitate extensive user engagement and the use of complex, expensive, and bulky instrumentation, ultimately limiting their use to specialized laboratory settings.

This dissertation presents multiple projects that focus on the engineering of microparticle systems to drive advancements in quantitative biomolecule detection approaches by simplification of signal transduction methods and assay processing requirements. To simplify signal transduction methods, we show proof-of-concept for a label-free, motion-based biomolecule detection system using active particles that propel via induced-charge electrophoresis (ICEP). We prepare induced- charge electrophoretic microsensors (ICEMs) for the capture of two model biomolecules and show that the specific capture of biomolecules leads to direct signal transduction through ICEM speed suppression at low concentrations. We further present dielectrophoretic polarizability measurement (DPM) as a method to study the effects of surface modifications on the polarizability of surfaces in systems that leverage induced-charge electroosmotic flows and study to the speed of surface-modified particles similar to ICEMs that propel by ICEP. Through use of this method, we show that ICEM speed suppression upon protein capture likely arises from both changes to the surface polarizability of the particle as well as interactions of the particle with solid surfaces.

To simplify assay processing requirements, we present a new a class of acoustic-responsive microparticles, termed functional negative acoustic contrast particles (fNACPs), and a handheld, ergonomic acoustic pipette for the rapid, sensitive, and user-friendly detection of biomolecules. The fNACPs are decorated with biorecognition motifs for the specific capture of target biomarkers from whole blood, and the acoustic pipette contains an acoustofluidic trapping channel in which fNACPs are robustly trapped and rapidly separated from whole blood. Using this system, we demonstrate the detection of an antibody biomarker from whole blood at picomolar levels. Finally, in a separate project, we present a multiplexed fNACP assay for the simultaneous detection of multiple biomolecules from single samples, as well as a high-throughput, siphon-based multichannel acoustic separator for the simultaneous separation of fNACPs from multiple samples. Overall, the findings presented in this dissertation provide numerous advancements in the fields of particle-based biomolecule detection, acoustofluidics, and electrokinetics, among others.