Development of a Water Quality Test Based on 3 Dimensional Dielectrophoretic Well Electrode Measurements of Fresh Water Algae.

Dielectrophoresis (DEP) describes the motion of a particle in a non-uniform alternating electric field induced by a dipole. Over the last 60 years it has been increasingly used for the purpose of non-invasive cell analysis and manipulation. The effects of which are predominantly governed by the dielectric properties of the particle with regards to the suspending medium, the electrode design and the frequency of the applied electric field. This thesis investigates the feasibility of using a 3D well electrode to perform dielectrophoresis on a population of algae cells, with the intention of producing a test procedure for the assessment of water quality. The well electrodes were used to produce dielectrophoretic spectra for the two strains of algae used in the recognised European and British standard for Water Quality - Freshwater algal growth inhibition test with unicellular green algae (BS EN ISO 8692:2004; BS 6068-5.10:2004). Experiments were performed for both strains of algae showing the effects for a range of cell concentrations on the DEP spectra. The effects on dielectrophoretic response are presented for a range of well electrode diameter sizes and the optimum radius was determined. An automated process for the vibration of the well electrode and the contained cell solution is also presented. The effects of vibration for each planar axis and paired combination are shown, for the potential use as an automated cell re-dispersion tool. Sedimentation of cells over time is recorded and the effect this could have on DEP results for sequential or prolonged experiments are discussed. The effectiveness of a method presented by Hubner et al (2003), describing how dielectrophoresis with needle electrodes on a population of algae cells can be used to perform rapid water quality analysis is discussed. Alternative experimentally verified conclusions are presented showing proportional changes in cell concentrations in relation to toxicology