Electrodynamic droplet actuation for lab on a chip system

Abstract

This work presents the development of electrowetting on dielectric and liquid dielectrophoresis as a platform for chemistry, biochemistry and biophysics. These techniques, typically performed on a single planar surface offer flexibility for interfacing with liquid handling instruments and performing biological experimentation with easy access for visualisation. Technology for manipulating and mixing small volumes of liquid in microfluidic devices is also crucially important in chemical and biological protocols and Lab on a Chip devices and systems. The electrodynamic techniques developed here have rapid droplet translation speeds and bring small droplets into contact where inertial dynamics achieve rapid mixing upon coalescence.In this work materials and fabrication processes for both electrowetting on dielectric and liquid dielectrophoresis technology have been developed and refined. The frequency, voltage and contact angle dependent behaviour of both techniques have been measured using two parallel coplanar electrodes. The frequency dependencies of electrowetting and dielectrophoretic liquid actuation indicate that these effects are high and low-frequency limits, respectively, of a complex set of forces. An electrowetting based particle mixer was developed using a custom made electrode array and the effect of varying voltage and frequency on droplet mixing was examined, with the highest efficiency mixing being achieved at 1 kHz and 110 V in about 0.55 seconds.A composite electrodynamic technique was used to develop a reliable method for the formation of artificial lipid bilayers within microfluidic platforms for measuring basic biophysical aspects of cell membranes, for biosensing and drug discovery applications. Formation of artificial bilayer lipid membranes (BLMs) was demonstrated at the interface of aqueous droplets submerged in an organic solvent-lipid phase using the liquid dielectrophoresis methods developed in this project to control the droplet movement and bring multiple droplets into contact without coalescence. This technique provides a flexible, reconfigurable method for forming, disassembling and reforming BLMs within a microsystem under simple electronic control. BLM formation was shown to be extremely reliable and the BLMs formed were stable (with lifetimes of up to 20 hours) and therefore were suitable for electrophysiological analysis. This system was used to assess whether nanoparticle-membrane contact leads to perturbation of the membrane structure. The conductance of artificial membranes was monitored following exposure to nanoparticles using this droplet BLM system. It was demonstrated that the presence of nanoparticles with diameters between 50 and 500 nm can damage protein-free membranes at particle concentrations in the femtomolar range. The effects of particle size and surface chemistry were also investigated. It was shown that a large number of nanoparticles can translocate across a membrane, even when the surface coverage is relatively low, indicating that nanoparticles can exhibit significant cytotoxic effects