Dielectrophoresis and its applications in biochips

Cell manipulation and separation has numerous biological and medical applications, e.g., identification and characterization of individual cells, purification of cell subpopulations from mixture suspension, etc. Dielectrophoresis, the movement of particles in non-uniform AC electric field, is of tremendous interest for these applications at the micro and nanoscale. Dielectrophoresis on micro-fabricated electrodes has been proved especially suitable due to its relative ease of micro-scale generation and structuring of an electric field on microchips. Furthermore, integrated dielectrophoresis biochips provide the advantages of speed, flexibility, controllability, and ease of application to automation. In this thesis, we first present experimental results to demonstrate the basic concept of manipulation and separation of live and heat-treated cells of Listeria on the micro-fabricated devices with interdigitated electrodes by utilizing the difference of dielectric properties between live and dead cells with respect to the suspending medium. Based on this, a microfluidic biochip was then designed and fabricated in silicon substrate with a 12 μm deep chamber and anodic-bonded glass cover. We present experimental results and finite element modeling of the holding forces for both positive and negative dielectrophoretic traps within this dielectrophoretic device. The experimental results and those from modeling are found to be in close agreement, validating our ability to model the dielectrophoretic filter for bacteria, spores, yeast cells, and polystyrene beads. A dynamic simulation was further carried out to optimize the device. All of the knowledge can be very useful in designing and operating a dielectrophoretic barrier or filter to sort and select particles entering the microfluidic devices for further analysis. Last, in order to overcome the inefficiency of dielectrophoretic separation of similar biological species, a novel method was proposed to selectively capture target bacteria using the combination of dielectrophoresis and antibody recognition. Great selectivity has been achieved by using our established experimental protocol