Detection of saxitoxin in counterterrorism using a commercial lateral flow immunoassay kit

The neurotoxin saxitoxin (STX) is registered in the list of the Chemical Weapons Convention. In preparation against potential terrorism by STX use, we investigated the performance of a commercially available rapid test kit for paralytic shellfish poisoning (PSP), which is essentially a lateral flow immunoassay kit. Pink lines in the test and control zones appeared after 35 min and were observed by the naked eye and were recorded by a digital scanner. The competitive displacement of gold-labeled antitoxin analog antibody by STX in the test zone was quantitatively shown using the ratio of the intensity of the test zone line to that of control zone line. As the STX concentration increased, the intensity of the pink line in the test zone on the strip decreased. The limit of detection was defined as the STX concentration that gave a ratio half that of the STX blank test, and was calculated to be about 12 ng/ml. Various matrix components, such as wheat flour and the decontamination chemical hypochlorite, were examined for their effects on false positive and false negative results in the determination of STX by the PSP Rapid Test system.