Ganglioside-liposome immunoassay for the ultrasensitive detection of cholera toxin

An extremely sensitive bioassay has been developed for cholera toxin (CT) detection, using ganglioside-incorporated liposomes. Cholera is a diarrheal disease, often associated with water or seafood contamination. Ganglioside GM1 was used to prepare the liposomes by spontaneous insertion into the phospholipid bilayer. CT recognition and signal generation is based on the strong and specific interaction between GM1 and CT. In a sandwich immunoassay, CT was detected as a colored band on the nitrocellulose membrane strip, where CT bound to GM1-liposomes can be captured by immobilized antibodies. The intensity of the band could be visually estimated or measured by densitometry, using computer software. The limit of detection (LOD) of CT in the assay system was found to be 10 fg/mL which is equivalent to 8 zmol in the 70-microL sample. The assay was also tested with water samples spiked with CT, providing a LOD of 0.1-30 pg/mL, which is much better than previously reported limits of detection from other assays. The assay could be completed within 20 min. These results demonstrate that the bioassay developed for CT is rapid and ultrasensitive, suggesting the possibility for detecting CT, simply and reliably, in field screening.