The secondary antibody has an attached enzyme, horseradish
peroxidase (HRP). In the last step, the attached HRP enzyme
catalyzes color development in the substrate, OPD. The optical
density of the substrate is then measured and is inversely
proportional to aflatoxin concentration.
Aflatoxin concentrations were measured using 96-well
polystyrene microplates that had previously been coated with
AfB1-BSA-conjugate. The AfB1-BSA coated plates were
prepared as follows: To the wells of new microplates, 100 μL
AfB1-BSA-conjugate (5 mg/L) in pH 9.5 carbonate/bicarbonate
buffer were added and equilibrated overnight in a
refrigerator. The coated plates were subsequently washed 6
times using phosphate buffered saline with 0.05% Tween 20
(PBST) and stored dry in a refrigerator until use.
Aliquots (50 μL) of aflatoxin standards containing 0 to
500 ng AfB1/mL in 12% methanol/88% PBST were added to
the wells of AfB1-BSA coated plates. Similarly, blanks and
sample solutions were diluted using 12% methanol/88% PBST
and 50-μL aliquots added to the wells of the microplates.
Then, 50-μL aliquots of a 1:2000 dilution of the rabbit anti-
AfB1 antibody in PBST were added to the microplate wells
and the microplates agitated for 2 h. Afterward, the