Designing Microfluidic Components For Analyte Concentration and Identification Using AC Electrokinetics

Microfluidics and nanofluidics have recently been on the forefront of new medical devices and new technologies. Due to their ability to adapt to medical and environmental systems, these mechanisms have the capability of replacing standard laboratory techniques with a field applicable rapid diagnostic device. The main problem that is preventing these devices from becoming a viable kit lies in the large discrepancy between the concentrations of the target bioparticle in realistic samples (~100 colony forming units (CFU)/ml) and the concentration thresholds of the on-chip detection mechanisms (~10^6 CFU/ml). Current standards require culturing to amplify the concentration to reach these detection thresholds; however this step is time and laboratory intensive. Alternatively, by taking advantage of the microfluidic characteristics inherent in the chip-scale devices and using AC electrokinetics, manipulation of the bioparticles can be done on-chip, eliminating the bottleneck in the detection time.The advantage of using microfluidics and AC electrokinetic mechanisms is that fluid forces and particle specific forces such as dielectrophoresis and electroosmotic flow can be combined to induce forces that are not only fast and far reaching into the bulk (~1 cm/s) but also specific to the particle's characteristics (permittivity, size, etc.). In particular, the forces that are particle specific tend to only act as short-range forces, acting on the order of 10-100 Ì_å_m from surface. On the other hand, forces that are fast and far reaching in the bulk will act as a long-range force but are not particle specific. Thus by combining these forces in a microvortex, a continuous flow and an AC electroosmotic flow system, bioparticles can be concentrated, sorted, and confined to specific regions on a chip sized device.Detection systems can be integrated into these devices such as Raman spectroscopy and surface-enhanced Raman scattering to detect bacteria and other bioparticles. In particular the manipulation and crystallization of smaller bioparticles such as protein molecules are influenced by the applied AC field which can be tuned to enhance the quality and the size of the crystal grown. In this system, it is speculated that the AC field is not only manipulating the protein molecules themselves, but also disrupting the hydration cage surrounding the molecules, allowing them to interact which increases the probability that nucleation and crystal growth will occur. With the combination of these AC electrokinetic short-range particle specific forces and the long-range bulk forces, it is shown that faster mechanisms can be generated to enhance concentration and detection techniques used on-chip. These advancements will improve the current standards for on-chip detection, allowing for faster diagnostics to be used in the field.