AC Electric Field Separation, Collection and Detection of Cells and Synthetic Particles

The goal of this dissertation is to develop new tools for the manipulation and characterization of specific cell types in AC electric fields. Cells are polarizable and resistive, therefore, it is possible to manipulate and detect cells using AC electric fields. Novel bio-microfluidic devices using two AC field techniques, AC electrokinetics and impedance spectroscopy, were developed to collect, trap and detect cells and particles in electrolyte suspensions.;First, a new device was constructed to collect cells and particles in a predetermined area on the chip, using AC fields to drive fluid flows with AC electrokinetic phenomena over asymmetric planar electrodes. When an electric field is applied to asymmetric electrodes, the ionic charge mobility above the electrodes creates small eddies of fluid flow, drawing the bulk of the fluid in a manner analogous to a conveyor belt. The gold-on-glass planar asymmetric electrode pattern uses AC electrosmotic (ACEO) pumping to induce equal, quadrilateral flow directed towards a stagnant region in the center of the electrode chip. A number of design parameters affecting particle collection efficiency were investigated including: electrode and gap width; chamber height; applied potential and frequency; number of repeating electrode pairs and electrode geometry. By optimizing these parameters, the device was proven capable of rapidly collecting particles in the stagnant region within six minutes. The robustness of the design was evaluated by varying electrolyte concentrations, particle types and particle sizes. During the evaluation with electrolyte suspensions of particles, the device was prone to electrochemical reactions at the electrode surface and cell suspensions tended to adhere to the glass substrate, reducing the overall particle collection efficiency. Several coatings (silanes, hydrogels and polyelectrolytes) over two electrode compositions (gold and platinum) were investigated to reduce or eliminate this effect. To confirm that the electrochemical reaction had been reduced for each coating type, cyclic voltammetry studies were performed. Platinum exhibited the most promising performance for device robustness. Preliminary analysis suggests polyelectrolytes to be the most effective for reducing electrochemical effects on the electrodes; however the silanes were superior in the reduction of biofouling. These devices are amenable to integration with a variety of cell detection lab-on-a-chip methods, and specifically, are compatible with optical evanescent waveguide detection technique.;The second part of the dissertation focuses on impedance-based cell detection, and the characterization of interdigitated gold electrode devices as well as methods to detect specific cell types by agglutination. Impedance is the resistance and capacitance in an electric circuit while impedance spectroscopy is the measure of impedance over varying applied frequencies at a fixed current and voltage. The effects of agglutination techniques and suspension characteristics on the impedance spectroscopy of yeast/latex particle, yeast/gold nanoparticle and yeast/magnetic particle suspensions were investigated. All of the agglutinated systems demonstrated a distinct, repeatable impedance change versus the non-agglutinated systems, showing impedance spectroscopy across interdigitated electrodes is sufficient to detect distinct agglutinated suspensions. Improving upon existing impediometric detection devices, biospecific ligand-functionalized magnetic particles were used to draw the agglutinated suspensions to the electrodes. To improve the device further, it was inverted so that cells bound exclusively to specifically functionalized magnetic particles. The bound particle and cell conglomerates were manipulable using magnetophoresis and brought to the electrode surface. The bio-chip impedance spectroscopy technique could be extended to determine the feasibility of using impedance spectroscopy methods in a system with fluid flow, to systems with multiple cell types and be of potential use in new novel biomaterials, biosensors, and microdevices.