Electrochemical detection of immobilised Neuro-2a cell viability: a first step towards biosensors for neurotoxins.

Ciguatoxins (CTXs), produced by microalgae within the Gambierdiscus and Fukuyoa genera, and tetrodotoxins (TTXs), produced by bacteria, are one of the most potent emerging natural marine toxins in Europe, which act by selectively blocking the action potentials of voltage-gated sodium channels (VGSCs) in nerves, skeletal and cardiac muscle membranes, with opposite mechanisms of action. CTXs block them in an open position, whilst TTXs do it in a closed state.

For the European Food Safety Authority (EFSA), these neurotoxins have been the primary concerns due to the important impact on human health, and their important effects on food safety. The evaluation and characterisation of their risk with adequate detection methods for monitoring procedures are crucial to protect human health. EFSA also encourages the search for occurrence data and the development of reliable and efficient analytical methods. However, despite technological advances, there are still methodological uncertainties and high demand for universal marine toxins detectors. Electrochemical cell-based biosensors seem a promising strategy, which are based on cell-based assays (CBAs) and therefore measure the toxicological effect of toxins on cells and provide an estimation of the composite toxicity of a sample and have the added advantage of the high sensitivity provided by electrochemical detection techniques.

Bearing that in mind, Neuro-2a cells were immobilised on electrodes of different materials, and their viability was assessed using a tetrazolium salt. After optimisation of the assay conditions, the effect of CTX and TTX standard solutions on the immobilised cells was evaluated. Finally, the system was applied to the analysis of fish extracts containing CTX (Variola louti) and TTX (Lagocephalus sceleratus), as a proof of concept. The strategy has been proved to be successful and therefore paves the way towards the development of electrochemical cell-based biosensors for the detection of marine neurotoxins.