Polyclonal antibodies to 7-hydroxycoumarin - the main metabolite of coumarin, a plant constituent with many clinical applications - were produced, purified and characterised. This antibody preparation was used to develop a competitive immunoassay for 7- hydroxycoumarin which was carried out on the BIAcore, an optical biosensor based on the phenomenon of surface plasmon resonance (SPR). The immunoassay was optimised and internally validated. Monoclonal antibodies were generated by somatic cell fusion using the spleens of mice immunised with a 7-hydroxycoumarin-protein conjugate. The screening of cell culture supernatants by BIAcore and ELISA was compared, and all of 13 clones isolated by limiting dilution were found to be reactive to the drug-protein conjugate, but not to free drug. The panning of phage displayed antibodies from a naïve library using the BIAcore was investigated, and, although the amount of bound phage was insufficient to generate an SPR signal, subsequent analysis of eluate demonstrated that enrichment had taken place. BIAcore was also used to affinity rank a panel of 3 genetically-produced single chain Fv antibodies against coumarin-BSA and to examine kinetic and affinity data for the interaction of one of these antibodies with immobilised drug-protein conjugate. The interaction of two antibody preparations against the fungal toxin aflatoxin Bi (AFBj), a member of the coumarin family, was studied using both BIAcore and ELISA methods. High affinity constants rendered the monoclonal and polyclonal antibodies unsuitable for use in regenerable immunosensor formats. A range of competitive and sandwich ELISAs for the detection of AFBi were developed using both types of antibody. In addition, methods to facilitate better design of formats for use with BIAcore were established using ELISA to mimic regeneration conditions on the sensor chip surface, and to calculate equilibrium affinity constants. Supercoiled plasmid DNA was also immobilised on the BIAcore sensor surface, and the inhibition of the enzyme topoisomerase II by the coumarin antibiotic novobiocin, as well as the direct binding of a range of coumarin-protein conjugates to nucleic acids, were investigated.