The work described is primarily concerned with the understanding of the induced AC electrokinetic properties of latex particle complexes. The assays are based on the electrorotational response of elliptical latex particles to the binding of bacteria or biomacromolecular species. Two coliform bacteria systems were investigated, gram-negative £. coli and gram-positive B. subtilis. Latex particles were coated in antibodies against these two bacteria and this resulted in adhesion of the bacteria to the latex particles when placed together in an aqueous suspension. The electrorotational response of both viable and non-viable E.coli and B. Subtilis bound to particles was investigated. The resulting assay proved to be sufficiently sensitive to be able to detect at the single organism level and it was possible to measure the bound bacterial concentration. In addition., the bacteria possessed distinct electrorotational properties and it proved possible to distinguish between the two species. This section of the work is likely to be of benefit to the water and food industries. The effect of binding antibodies and nucleic acids to the surface of latex particles was also investigated. It was found possible to detect the presence of nucleic acid on the particle surface using electrorotation measurements. For antibody-coated particles, it was possible to distinguish between primary, secondary and tertiary antibody coating. In addition, binding of gold conjugated antibodies was found to elicit a considerably greater change in the electrorotational characteristics of the system. These findings have potential benefits in medical diagnostic applications.