Electrokinetic and acoustic manipulations of colloidal and biological particles

摘要

Recent advances in microfluidic technologies have enabled integration of thefunctional units for biological and chemical analysis onto miniaturized chips, called Labon-a-Chip (LOC). However, the effective manipulation and control of colloidal particlessuspended in fluids are still challenging tasks due to the lack of clear characterization ofparticle control mechanisms. The aim of this dissertation is to develop microfluidictechniques and devices for manipulating colloids and biological particles with theutilization of alternating current (AC) electric fields and acoustic waves.The dissertation presents a simple theoretical tool for predicting the motion ofcolloidal particles in the presence of AC electric field. Dominant electrokinetic forcesare explained as a function of the electric field conditions and material properties, andparametric experimental validations of the model are conducted with particles andbiological species. Using the theoretical tool as an effective framework for designingelectrokinetic systems, a dielectrophoresis (DEP) based microfluidic device for trappingbacterial 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 sporeson patterned surfaces is successfully demonstrated. A further investigation of DEPcolloidal manipulation under the effects of electrothermal flow induced by Joule heatingof the applied electric field is conducted. A periodic structure of the electrothermal flowthat enhances DEP trapping is numerically simulated and experimentally validated.An acoustic method is investigated for continuous sample concentration in amicroscale device. Fast formation of particle streams focused at the pressure nodes isdemonstrated by using the long-range forces of the ultrasonic standing waves (USW).High frequency actuation suitable for miniaturization of devices is successfully appliedand the device performance and key parameters are explained.Further extension and integration of the technologies presented in thisdissertation will enable a chip scale platform for various chemical and biologicalapplications such as drug delivery, chemical analyses, point-of-care clinical diagnosis,biowarfare and biochemical agent detection/screening, and water quality control.