Extraction-Less Amperometric Detection of Tetrodotoxin in Seawater

Tetrodotoxin (TTX), a potent neurotoxin, has recently been detected in marine fauna and waters in multiple locations outside its historical range and is projected to increase in both stability and bioavailability in acidifying oceans. We report the first biosensor designed to detect sub-ng ml−1 concentrations of TTX directly in natural seawater. The compact sensor chip employs a competitive enzyme strategy with a glucose oxidase-TTX conjugate that generates an amperometric response in the presence of a ferricyanide redox mediator. The biorecognition layer synthesis is confirmed by attenuated total reflection Fourier transform infrared spectroscopy. Cyclic voltammetry and electrochemical impedance spectroscopy are used to probe the stability and hydrophilicity of the biorecognition layer. We investigate the effects of nonspecific adsorption on sensor results and find that bovine serum albumen is an excellent blocking agent for preventing NSA when incubating with filtered seawater samples. The biosensor has a limit of detection of 0.053 ng ml−1 and a sensitivity of 87 nA ng−1 ml. Requiring no extraction or preconcentration steps with a time-to-results of under an hour, our biosensor provides a new tool for detecting TTX in natural waters, which can lead to more proactive monitoring and higher throughput testing.