The development of procedures based on the principles of immunoassay have proved to be of major significance in clinical chemistry. Variations of the technique have made possible the assay of haptens and proteins and resulted in a million-fold increase in sensitivity over previous methods. The increasing availability and usefulness of radioimmunoassay (RIA), however, has raisin several problem and several non-isotopic alternatives hate been proposed. In particular, immunoassacs monitored by chemiluminescence (CIA) have been developed for the measurement of steroids in extracts of peripheral plasma and steroid glucuronides in samples of diluted urine.
The labelled antigens were sythesised by covalent linkage of a steroid glucuronide or carboxy derivative of a steroid to isoluminol through an alkyl chain of varying length. The resulting conjugates produced light upon oxidation with hydrogen peroxide in the presence of microperoxidase with a detection limit in the fmol range. The chemiluminescence reaction conditions have been optimised in terms of the concentration of enzyme and hydrogen peroxide. In addition, the effects of pH and mode of measurement have been investigated. Monoclonal antibodies were produced, characterized and have been used for the development of away, and its potentials is discussed.
Several homogeneous liquid-phase immunoassays, based upon antibody-enhanced chemiluminescence and antibody-quenced chemiluminescence have been developed. These procedures have been shown to have excellent sensitivity and specificity but are subject to interference from biological samples. Consequently, solid-phase (antibody coated plastic tubes) and liquid-phase (with dextran-coated-charcoal separation) heterogeneous CIAs have been devised and these produres have been evaluated in terms of sensitivity, specificity accuracy and precision. Multiple immunoassay which can measure two or more analytes in a single tube, has been developed. In addition, comparisons have been made between the CIAs and their equivalent RIAs. The potential and future development of CIA is discussed.
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