Enzyme immunoassay with captured hapten. A sensitive gastrin assay with biotinyl-gastrin derivatives.

Two N-terminal biotinyl-gastrin derivatives were synthesized to investigate the effect of the length and chemical properties of the biotin-spacer on both the capture of the hapten by streptavidin or avidin adsorbed on polystyrene, and the antigenicity of the captured peptide. The observed full retainment of antibody binding capacity of the biotinyl-gastrins upon their immobilization, allowed to develop a sandwich-type ELISA with a sensitivity of one order of magnitude better than the standard ELISA with polystyrene-adsorbed gastrin. This hapten capture system reduces desorption particularly pronounced for low mass peptides, and avoids possible modifications or suppression of epitopes by the adsorption process with concomitant reduction of antibody binding affinity of the antigen. This new type of assay procedure may also represent a useful tool particularly for epitope mapping with relatively low mass synthetic protein fragments.