Development of ultrasensitive direct chemiluminescent enzyme immunoassay for determination of aflatoxin M1 in milk.

A direct competitive chemiluminescent enzyme-linked immunosorbent assay (CL-ELISA) for detecting aflatoxin M1 (AFM1) was developed. To improve the sensitivity of the assay, a mixture of 3-(10'-phenothiazinyl)-propane-1-sulfonate (SPTZ) and 4-morpholinopyridine (MORPH) was used to enhance peroxidase-induced CL. The concentrations of the coating anti-AFM1 antibody and the conjugate of AFB1 with horseradish peroxidase the conditions of the chemiluminescent assay were varied to optimise the condition of the chemiluminescent assay. The lower detection limit values and dynamic working range of CL-ELISA of AFM1 were 0.001 ng mL(-1) and 0.002-0.0075 ng mL(-1), respectively. A 20-fold dilution of milk samples prevented a matrix effect of the milk and allowed measurement of AFM1 at concentrations below than the maximum acceptable limit. Values of recovery within and between assays were 81.5-117.6% and 86-110.6%, respectively. The results of using the developed CL-ELISA to analyse samples of six brands of milk that were purchased in Taiwan revealed that AFM1 was absent from all studied samples.