Electrokinetic manipulation of micro to nano-sized objects for microfluidic application

This thesis describes experimental and numerical investigations of various electrokinetic techniques on fluorescent particles, bacteria and protein motors. The aim of this work is to extend the knowledge on the object manipulation, which is an essential part of a practical microfluidic device. The dissertation consists of three major sections that contain novel approaches to object manipulation using electric fields. The effect of dielectrophoretic force on fluorescent particles is analysed first. Using an experimental setup with a controlled switch for the input signal, the theoretical framework for amplitude modulated responce of dielectrophoretic force is developed. Also presented is the image processing software for quantitative particle motion analysis. Another analysis of various electrokinetic techniques (dielectrophoresis, AC electroosmosis, AC electrothermal flow and electrophoresis) was carried out on Pseudomonas Fluorescence bacteria in a solution that supports its growth. These bacteria usually live in geometrically restricted spaces and so spatially confined transparent channels were created to mimic their natural environment. It was noted that in these conditions the motile bacteria do not experience the effect of dielectrophoretic force. The minimum frequency that can be applied to the solution without forming bubbles is too high to distinguish AC electroosmotic effect. Using the numerical simulation, however, the experimental setup that utilises the observed effect of electrophoresis and AC electrothermal flow is designed. The final study was carried out on protein molecular motors. The novel experimental setup to investigate the effect of the electric field on the actin filament motility on five different surfaces, covered with myosin II motors, was developed. The application of higher external electric fields resulted in different velocity increases on different surfaces. Using the numerical simulation, this difference is quantitatively explained by the variation of the number of motors on surfaces. Also presented is a novel method that enables determining the forces exerted by the population of active and resistive motors without the need of expensive equipment

Models of nanoparticle transport in dielectrophoretic microdevices: prediction, parameter estimation and other applications

This paper describes the applications of Fourier Bessel series models for characterising the transport of nanoparticles driven by dielectrophoretic forces and randomized by Brownian motion. Nanoparticle transport using dielectrophoresis continues to be an active area of research and models are fundamental for characterising the process. The models have very useful capabilities including prediction of nanoparticle transport, estimation of parameter values from experimental data, and data decomposition into space and time components. The models also give a frequency domain representation that will be applicable for time modulated dielectrophoretic nanoparticle transport