IN-LINE MICROFLUIDIC PARTICLE PRECONCENTRATOR AND DETECTOR FOR CONTINUOUS FLOW MONITORING

This dissertation presents the design and prototyping of three in-line microfluidic devices for continuous monitoring of particulate flows. The three devices are AC electrokinetic (ACEK) and acoustic sample preconcentration techniques for resettable particle enrichment, and an in-line somatic cell counter for mastitis monitoring.

For the ACEK preconcentrator, ACEK is a new and promising technique to manipulate micro/bio-fluid and particles. There are many advantages over other techniques, such as low applied voltage, low cost, portability and notable biocompatibility of lab-on-a-chip (LOC) device. We successfully developed a 3D multi-level electrode platform to extract bioparticles via AC electroosmosis (ACEO) and negative Dielectrophoresis (DEP). Based on ACEO and N-DEP, the device can exert a drag force on particles through fluid motion and collect and concentrate particles. Optimization with respect to AC frequency, external pumping rate and opening size of mesh electrode have been performed.

This research also studies the concentration effect by acoustic wave on diatom cells in seawater environment, since ACEK has limitation in high conductivity medium. Acoustic trapping uses mechanical resonance to focus the target particles into the designated trapping area. It has the advantages of high trapping efficiency, contactless trapping and compatibility with various fluids. Furthermore, since the trapping effect and the vertical trapping location are dependent on the particle properties, binary particle separation and sorting are also highly possible.

Another contribution of this dissertation is the ACEK based capacitive somatic cell counter for use in dairy industry. Using our design, capacitive sensing is capable of detecting and quantifying target concentration in many types of biological solutions. The capacitance changing rate of device can be correlated with different concentrations of somatic cells. In this work, we successfully detected the concentration level of somatic cells in raw milk. The results were verified by flow cytometry.