Immunosensor array platforms based on self-assembled dithiols for the electrochemical detection of tetrodotoxins in puffer fish

The recent detection of tetrodotoxins (TTXs) in European fish and shellfish has emphasized the urgent need to develop specific, selective, rapid and easy-to-use methods for their detection to assess the potential risk posed to human health. For this purpose, a dithiol self-assembled monolayer (SAM)-based immunoassay previously performed on maleimide plates (mELISA) has been adapted to gold electrode arrays for the development of an electrochemical immunosensor for TTX. The electrochemical SAM-based immunosensor designed herein, provided an oriented, stable and spaced sensing platform for the determination of TTX, attaining a limit of detection of 2.6 ng mL^-1. The applicability of the biosensor array was demonstrated by the accurate quantifications obtained in the analysis of different tissues of several puffer fish species (Lagocephalus lagocephalus, L. sceleratus and Sphoeroides pachygaster) caught along the Mediterranean coast of Spain. The good agreements found between the TTX concentrations determined by the immunosensor array platforms and those determined by mELISA, surface Plasmon resonance (SPR) immunosensor and liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis, proved the feasibility of the approach. The electrochemical immunosensor enables the determination of TTXs at levels as low as 0.07 mg TTX equiv. kg^-1 tissue, thus, well below the Japanese value of 2 mg TTX equiv. kg^-1 tissue used as a criterion to consider puffer fish safe for consumption. Compared to the colorimetric SAM-based approach, the immunosensor array described herein shows promise towards the development of disposable, portable and compact analysis tools applicable in monitoring programs for the surveillance of fishery products.