Development and comparison of two immunoassay formats for rapid detection of botulinum neurotoxin type A.

We have evaluated two formats of immunoassays for the rapid detection of Clostridium botulinum neurotoxin type A (BoNT/A), in assay buffer and various matrices (human serum and nasal swabs, fresh milk, sugar, flour and talcum). The two formats, a vertical-flow strip immunochromatography (ICT) and a small disposable immunoaffinity column (IAC), were selected because they are both rapid and readily usable in the field without sophisticated equipment. We utilised the same critical reagents to develop and optimise both assays, making it possible to compare the corresponding technologies on the same toxin preparations, without interference due to the properties of the antibodies. Results were interpreted using a standard statistical test (ANOVA) and showed little difference of sensitivity between matrices. Though both assays were completed in 40 min, the sensitivity of the IAC, evaluated at 0.45 pM (5 mouse LD50 units/ml), was 40 to 80 times better than that of the ICT. Furthermore, the sensitivity of the IAC assay was improved to 0.09 pM (1 mouse LD50 unit/ml) when performed on a 5-ml volume of human serum. Thus, the IAC appears to be one of the most sensitive and rapid assays for the detection of BoNT/A reported to date and, because it is also highly transportable, it is amongst the best suited for field diagnosis of BoNT/A poisoning.