Date of Graduation
Eberly College of Arts and Sciences
Stephen J. Valentine
In the past few decades, microfluidic technology has been developed rapidly in both fabrication methods and multifunctionality integrations, making it a powerful tool for a wider variety of biological applications. The device fabrication method has expanded from conventional polymer-based micro devices to 3D-printed micro devices, and allows multiple functions such as electric, optic, magnetic and acoustic to be integrated on a single platform. This dissertation focuses on method development of acoustic streaming-based microfluidics in bioanalysis such as immunoassay, enzyme kinetics and DNA fragmentation analysis. In this dissertation, a micromixer was developed based on acoustic streaming generated from sharp-edge structure vibration and achieved rapid and homogeneous mixing of fluids in microscale. Based on this mixing principle, an acoustic streaming-based microfluidic method was developed and performed all the fluid and particle operations of bead-based immunoassay including beads immobilization; active mixing of fluid for bead/target binding; active molecular exchange for reagent loading and washing. The capability of our micromixer is that enables simultaneous particle trapping and active molecular exchange in a dead-end microchannel avoid using magnetic beads or centrifugal forces. The small footprint, simple setup, and continuous flow operation of this acoustic streaming-based method makes it an attractive platform for continuous flow bead-based immunoassay. Additionally, by simply attaching a piezoelectric transducer onto a standard glass microscope slide, a new voltage-free ionization method called Vibrating Sharp-edge Spray Ionization (VSSI) was presented. The sharp-edge based device can generate a spray of liquid samples by either placing a droplet onto the vibrating edge of the glass slide or touching a wet surface with the glass edge. Small organic molecules, carbohydrates, peptides, proteins, and nucleic acids can be ionized through this method eliminating the need for a high electric field (~5000 V·cm−1) for spray generation. The simplicity and voltage free nature of VSSI make it an attractive option for field portable applications or analyzing biological samples that are sensitive to high voltage or difficult to access by conventional ionization methods. Lastly, a 3D printed microfluidics device integrated with a single vibrating sharp-tip mixer was demonstrated. A highly efficient mixing was achieved through acoustic streaming generated by the vibration of sharp-tip. Multiple streams of fluids can be mixed with minimal mixing length (~300 μm) and time (as low as 3 ms), and a wide range of working flow rates from 1.5 μL/min to 750 μL/min. A one-step enzyme kinetics measurement can be achieved by simply adjusting the flow rates of reagents loaded from three inlets in one experiment run, which eliminates the steps of preparing and handling multiple solutions thereby simplifying the whole workflow significantly. With the same integrated device, a DNA fragmentation method can also be achieved under continuous flow without the need of microbubbles. Genomic DNAs can be fragmented into 700 to 3000 bp fragments with a power consumption of 142.3 mW. Due to the small footprint, continuous flow and bubble free operation, and high fragmentation efficiency, this method demonstrated great potential for coupling with other functional microfluidic units to achieve an integrated DNA analysis platform.
Li, Xiaojun, "Harnessing Acoustic Streaming for Bioanalysis in Microfluidics" (2021). Graduate Theses, Dissertations, and Problem Reports. 8253.