Abstract
This study aimed at developing sensitive competitive enzyme-linked immunosorbent assays (ELISAs) for the banned Sudan dyes using polyclonal antibodies. Three different formats were developed and characterized in terms of sensitivity, selectivity and rapidity. A competitive indirect ELISA was developed, which showed an IC50 of 3.8 µg l–1. Two competitive direct ELISAs were also developed, in which the antibody was added before or simultaneously with the other reagents; the first showed an IC50 of 8.3 µg l–1 and the latter showed an IC50 of 4.9 µg l–1. Nevertheless, considering dilution of extracts which is needed to offset matrix interference, the limits of detection of the three formats were substantially the same (10 µg kg–1). The antibodies in all three test formats were able to recognize Sudan I and partially Sudan II, III and IV; no cross-reactivity was observed with the five edible dyes. Twenty food samples, including chilli powder, paprika, ketchup, and egg, were extracted by a simple sample preparation and very limited dilution. Extracts were analyzed by the developed competitive direct ELISA with the simultaneous addition of reagents. A good correlation was observed (y = 1.19x–10.0, r 2 = 0.991, n = 20) when the data was compared with that obtained through a conventional HPLC method.
Acknowledgement
This work was funded by the Italian Ministry for Universities (PRIN, prot. n. 2005030782_001).