The work described in this thesis involves the production and characterisation of antibodies and recombinant antibodies to aflatoxin Bi (AFBi), a potent mycotoxin and carcinogen. The antibodies produced were then applied for use in a surface plasmon resonance-based biosensor (BIAcore), which measures biomolecular interactions in ‘real-time’. Production of hapten-protein conjugates of the organophosphate pesticides chlorpyrifos and pirimiphos, and characterisation of antichlorpyrifos antibodies were also successfully performed. Rabbit polyclonal and single chain Fv (scFv) antibodies were produced to aflatoxin Bi. The scFv’s were produced from an established phage display system, which incorporated a range of different plasmids for scFv expression. Both sets of antibodies were used in the development of competitive ELISA’s and also for the development of BIAcore-based inhibition immunoassays. The antibodies were also used in the detection of AFBi in spiked grain samples by ELISA and BIAcore. Both the polyclonal and scFv antibodies were found to be suitable for the detection of AFBi, and the assays were reproducible. The production of an activated form of the organophosphate pirimiphos for the production of a pirimiphos-protein conjugate was attempted. However it was not possible to conjugate this pesticide by any suitable means. Chlorpyrifos-BSA conjugates were produced with different molar substitution ratios, and were used for the development of a competitive ELISA with polyclonal anti-chlorpyrifos antibodies.