Abstract: A method of assaying a ligand in a sample which method includes the steps of contacting the sample with components comprising(a) a specific binding partner to the ligand and, if desired,(b) at least one reagent selected from ligand analogues and specific binding, partners,at least one of the said components (a) and (b) being labelled with an electron-donor or electron-acceptor,and determining whether (and, if desired, the extent to which) transfer of electrons between the said electron-donor or electron-acceptor label and a suitable charge-transfer partner resulting in charge-transfer complex formation is perturbed by ligand complex formation and/or by controlled external influences.

Abstract: A method of immunoassay of an antigen in a liquid sample wherein a complex is formed between antigen contained in the said sample and two or more antibody reagents, and the said complex is bound to a solid support by non-covalent bonding as defined herein; and the amount of complex becoming bound to the support is determined; the process employing at least one monoclonal antibody reagent. Labelling methods including radio-active, fluorimetric and enzyme labelling may be used to effect determination of the binding of the complex to the solid support. The solid support may take the form of particles, beads, wall-coatings on the reaction vessel or an insert of large surface area. The method is particularly applicable to the assay of TSH, CEA, HCG, alphafeto protein, immunoglobulins, viruses, allergens, bacteria, toxins, drugs and vitamins. Use of monoclonal reagents improves the specificity of the process, and also decreases non-specific binding.