This thesis describes the development of biosensing systems incorporating eukaryotic cells. The ultimate objective of this work was to design devices capable of rapidly assessing the toxicity of effluents and environmental pollutants. Although much work remains to be done in order to achieve this goal, the work reported here demonstrates, in principle, the approaches adopted. The first approach exploited the reducing nature of healthy biological cells. So called 'redox mediated whole cell biosensors' have been described before. In this work, an algal toxicity test of short duration was developed and sensors incorporating cultured fish cells were described for the first time. The sensitivity of biosensors incorporating the green alga Selenastrum capricornutum, to diuron and pentachlorophenol, was found to compare favourably with that from other standard ecotoxicological tests. However, although the sensitivity of biosensors incorporating immobilised BF-2 fish cells was found to compare well with that of other fish cell-based toxicity tests, it appeared that whole organism tests were much more sensitive to the compounlds tested. The second approach involved the genetic manipulation of fish cells in order to incorporate luminescent reporter genes. Although this work is less well advanced, it demonstrates that the luc reporter gene can be successfully inserted into BF -2 fish cells and that these transformed cells can produce a luminescent response when incubated with luciferin substrate. Preliminary investigations have indicated that the sensitivity of luc-transformed BF-2 cells to 4-chlorophenol is comparable to that of some standard whole organism ecotoxicological tests and although much work is still required to validate this approach, it could eventually provide a simple, sensitive and rapid route to toxicity assessment.

This thesis presents the development and characterisation of an ultra-sensitive, silicon nanowire (SiNW)-based biosensor devices for the detection of disease biomarkers.

Schistosomiasis is a parasitic disease affecting over 200 million people worldwide. This study reports the design and development of a microfiltration device for isolating schistosome eggs in urine for rapid diagnostics of urogenital schistosomiasis. The design of the device comprises a linear array of microfluidic traps to immobilize and separate schistosome eggs. Sequential loading of individual eggs is achieved autonomously by flow resistance, which facilitates observation and enumeration of samples with low-abundance targets. Computational fluid dynamics modeling and experimental characterization are performed to optimize the trapping performance. By optimizing the capture strategy, the trapping efficiency could be achieved at 100% with 300 mu l/min and 83% with 3000 mu l/min, and the filtration procedure could be finished within 10 min. The trapped eggs can be either recovered for downstream analysis or preserved in situ for whole-mount staining. On-chip phenotyping using confocal laser fluorescence microscopy identifies the microstructure of the trapped schistosome eggs. The device provides a novel microfluidic approach for trapping, counting and on-chip fluorescence characterization of urinal Schistosoma haematobium eggs for clinical and investigative application.

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