Direct competitive ELISA based on a monoclonal antibody for detection of aflatoxin B-1. Stabilization of ELISA kit components and application to grain samples

A direct competitive enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody has been developed and optimized for detection of aflatoxin B I (AFB(1)), and an ELISA kit has been designed. This immunoassay was highly specific, sensitive, rapid, simple, and suitable for aflatoxin monitoring. AFB(1) concentrations determinable by ELISA ranged from 0.1 to 10 mu g L-1. The IC50 value was 0.62 mu g L-1. Recovery from spiked rice samples averaged between 94 and 113%. The effect of different reagents on the stability of HRP-AFB(1) conjugate solution was studied. The performance of a stabilized enzyme tracer in ELISA was determined and compared with that of a freshly prepared control solution of HRPw-AFB(1) conjugate. The results showed that stabilizing media containing 0.02% BSA, 0.1% Kathon CG, and 0.05 mol L-1 calcium chloride in 0.05 mol L-1 Tris-HCl buffer (pH 7.2) maintained the activity of HRP-AFB(1) at a dilution of 1:1000 for a period of at least 12 months at room temperature whereas the reference conjugate solution without the additives lost its activity within a few days. Several additives were tested for their stabilizing effect on a monoclonal antibody (MAb) immobilized on the surface of polystyrene microtitre plates. It was shown that immobilized MAb, treated with post-coating solutions containing PVA, BSA, and combinations of these substances with trehalose, retained its activity for at least 4 months at 4 degrees C, whereas the untreated MAb-coated plate lost its activity within 2 days.