Harmful algal blooms (HABs) have significant detrimental effects on the environment and on food and water quality. Furthermore, toxins produced by some algal species may enter the food web via shellfish, finfish or by consumption of contaminated drinking water causing gastrointestinal disorders, liver damage and tumour promotion. This research focused on the algal toxins azaspiracid-1 (AZA1) and microcystin-LR (MC- LR). In addition, the Gram positive bacterium, Bacillus cereus, is a ubiquitous foodborne pathogen with severe health implications. Strict controls are imposed on the levels of these food contaminants and national monitoring programs help to ensure consumer safety. Biosensor technology affords a viable approach to monitor food contaminants with high sensitivity and low cost. In addition, the ability to fully automate such systems allows the possibility for fully autonomous, in situ monitoring systems for algal toxins and for species-level identification of harmful bacterial species. This thesis describes the development and optimisation of recombinant antibody fragments specific to AZA1 and MC-LR for incorporation into such biosensor systems. An anti-AZA1 scFv library was developed but screening programs could not isolate AZA1-specific clones. However, a competitive assay, using polyclonal antibodies, was developed which could detect 1.19 ng/mL of AZA1. A previously developed anti-MC-LR scFv, designated 2G1, was studied by in silico computational modelling and targeted mutagenesis, which allowed for improvements in both antigen-binding and protein stability. An anti-B. cereus scFv library was developed and screened which allowed for the enrichment of clones generating antibodies with preferential binding to B. cereus. This research also focused on investigating the effects of AZA1, MC-LR, and the cyanobacterium Microcystis aeruginosa on the human hepatocellular carcinoma cell line, HepG2. The effects of individual and combined exposure to these contaminants was determined used High Content Analysis. The results demonstrated that AZA1 displayed cytotoxic and apoptotic effects on HepG2 cells, whereas MC-LR exposure resulted in both proliferative and necrotic effects. Co-exposure to MC-LR and AZA1 resulted in antagonistic effect whereas synergistic effects were observed for co-exposure to MC-LR and M. aeruginosa.