Paralytic shellfish poisoning (PSP) due to consumption of contaminated shellfish is an increasing problem is the coastal waters of the United States, particularly in New England and the Pacific Ocean. The symptoms of PSP include vomiting, diarrhea, shortness of breath, confusion, and loss of coordination in both marine animals and humans. In severe cases, PSP toxins can cause respiratory failure and death within hours if care is not provided. PSP is precipitated by neurotoxins produced by marine algae, which accumulate in the flesh and viscera of commercially important shellfish species. Currently, US state agencies monitor for the presence of toxic phytoplankton and when the cell count reaches a set level, shellfish beds are tested for the presence of toxin. However, current methods for detection of PSP toxins have serious drawbacks, including lengthy assay time, cost, and false positive and negative results. The purpose of this project is to develop a fluorescence based receptor binding assay for the detection of PSP neurotoxins. A fluorescent sensor based on a molecule that binds at the PSP toxin receptor site (tetrodotoxin) will allow for low cost rapid assays with high specificity for toxic samples, thus limiting false positive and negative results.