Abstract
In this thesis, two novel enzyme immunoassay protocols that had been considered in theory were studied in practice. One protocol involved the use of multi-enzyme systems in order to simultaneously quantitate more than one component of a biological fluid. A model dual hapten method was developed in which alkaline phosphatase was conjugated to thyroxine, and B-galactosidase was linked to triiodothyronine. The choice of these two enzymes enabled each to be measured in the presence of the other without cross detection and provided the means for the determination of both thyroid hormones in a single tube. The assay compared well with existing radioimmunoassay techniques and confirmed that the theoretical advantages of the method, in time and cost saving, could be achieved in practice. The other new protocol investigated involved the use of an enzyme inhibitor as a label in an homogeneous system. Homogeneous assays possess the features of rapidity and ease of automation which can be of significant advantage in a routine laboratory. Enzymes have been used directly as labels in homogeneous methods but the use of an enzyme inhibitor label would, in theory, be a simpler process. A series of problems prevented the development of a model method based on this principle although the experimental work carried out did enable a better appreciation of the essential requirements of the proposed system to be gained. A final evaluation concludes that both protocols have potential for future use.