Electrokinetic and acoustic manipulations of colloidal and biological particles



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Recent advances in microfluidic technologies have enabled integration of the functional units for biological and chemical analysis onto miniaturized chips, called Labon- a-Chip (LOC). However, the effective manipulation and control of colloidal particles suspended in fluids are still challenging tasks due to the lack of clear characterization of particle control mechanisms. The aim of this dissertation is to develop microfluidic techniques and devices for manipulating colloids and biological particles with the utilization of alternating current (AC) electric fields and acoustic waves. The dissertation presents a simple theoretical tool for predicting the motion of colloidal particles in the presence of AC electric field. Dominant electrokinetic forces are explained as a function of the electric field conditions and material properties, and parametric experimental validations of the model are conducted with particles and biological species. Using the theoretical tool as an effective framework for designing electrokinetic systems, a dielectrophoresis (DEP) based microfluidic device for trapping bacterial spores from high conductivity media is developed. With a simple planar electrode having well defined electric field minima that can act as the targetattachment/ detection sites for integration of biosensors, negative DEP trapping of spores on patterned surfaces is successfully demonstrated. A further investigation of DEP colloidal manipulation under the effects of electrothermal flow induced by Joule heating of the applied electric field is conducted. A periodic structure of the electrothermal flow that enhances DEP trapping is numerically simulated and experimentally validated. An acoustic method is investigated for continuous sample concentration in a microscale device. Fast formation of particle streams focused at the pressure nodes is demonstrated by using the long-range forces of the ultrasonic standing waves (USW). High frequency actuation suitable for miniaturization of devices is successfully applied and the device performance and key parameters are explained. Further extension and integration of the technologies presented in this dissertation will enable a chip scale platform for various chemical and biological applications such as drug delivery, chemical analyses, point-of-care clinical diagnosis, biowarfare and biochemical agent detection/screening, and water quality control.