Spin Immunoassay for Drug Determination

Abstract

Immunoassay for various drugs and foreign chemicals in biological fluids has become a routine, sensitive and reliable technique. Its principal drawback in routine clinical and forensic laboratories is the requirement for multiple sample manipulation and ultimate separation of the labelled from the unlabelled chemical. The use of electron spin resonance (ESR) as the detection system allows a greatly simplified procedure.

• 1. An antibody-labelled antigen complex is prepared (the ‘label’ is an unpaired electron).

• 2. This complex is mixed with the sample (the only mixing step).

• 3. The ESR absorption of the displaced label is determined.

The main advantage is achieced in step (3): no separation of antibody-labelled antigen complex from displaced labelled antigen is required (nor radioactivity measurement); only the unbound form resonates and is easily quatitated from a standard curve. In another application, binding to endogenous protein in blood or a tissue homogenate may be quantitated directly, by first measuring the resonance absorption of the free, labelled chemical and then the decrease on adding the test material.