The Thymulin ELISA test principle is based on a competition between the antigen in the sample or standards and biotinylated thymulin as a tracer for the binding sites of anti-thymulin antibodies coated on the wells of the microplate.
A peroxidase-conjugated steptavidin is used for detection and quantification, and tetramethylbenzidine (TMB) is used as a peroxidase substrate. An acidic stop solution terminates the enzymatic reaction.
A dose-response curve of the absorbance unit (optical density, OD at 450 nm) vs. concentration is generated using the values obtained from the standards. The presence of thymulin in the samples is determined directly from this curve.