Electrochemical Biosensor for the Assessment of Cell Viability Using Methylene Blue. Application to the Detection of Ciguatoxins in Fish from the Canary Islands.

Cell-based biosensors (CBBs) for the detection of marine neurotoxins such as ciguatoxins (CTXs) are of high interest due to the composite toxicological response they can provide and the low limits of quantification (LOQs) they can achieve with the use of sensitive neural cells. However, the development and validation of CBBs are challenging due to the use of living material and the need for appropriate signal transduction strategies. In this work, Neuro-2a cells have been immobilized on thin-film gold electrodes, and their viability after exposure to CTX1B has been evaluated with light optical microscopy as well as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using methylene blue (MB) as a redox indicator. An LOQ of 0.93 pg CTX1B/mL has been obtained. The CBB has been applied to the analysis of fish samples from the Canary Islands, one of them implicated in a ciguatera poisoning (CP) outbreak, and results have been compared with those obtained with a conventional cell-based assay (CBA), showing a very good agreement. The combination of the benefits of cells with those provided by biosensor platforms in terms of ease of use, miniaturization, automatization, and portability could result in the ideal analytical tool for CP management. Additionally, this is the first time MB is used as a cell viability indicator in a CBB, providing a new versatile approach for multiple applications.