Development of a Novel Biosensor-Based Rapid Detection Platform for Marine Biotoxins in Nigerian Coastal Waters

Marine biotoxins produced by harmful algal blooms pose severe threats to shellfish safety, fishery closures, and human health, yet current detection methods remain laboratory-based, expensive, and too slow for real-time coastal management applications in resource-limited settings. This research develops and validates a novel portable biosensor-based detection platform for paralytic shellfish toxins, domoic acid, and okadaic acid applicable for field deployment in Nigerian coastal monitoring programmes. The biosensor architecture integrates aptamer-based recognition elements with electrochemical impedance spectroscopy transduction on a graphene oxide-modified electrode substrate. Aptamers with high affinity and selectivity for each target toxin were selected using systematic evolution of ligands by exponential enrichment. Electrode modification and sensing chemistry were optimised through cyclic voltammetry, scanning electron microscopy, and X-ray photoelectron spectroscopy characterisation. Analytical performance was validated against certified reference materials and real environmental water samples from the Nigerian coast, with parallel comparison against regulatory mouse bioassay and ELISA methods. The optimised biosensor achieved detection limits of 0.42 micrograms per litre for saxitoxin, 0.18 micrograms per litre for domoic acid, and 0.38 micrograms per litre for okadaic acid, below regulatory trigger values for all three analytes. Specificity testing against 22 structurally related compounds confirmed selectivity greater than 0.95. The platform detected all 7 spiked environmental samples that were positive by reference ELISA methods. A prototype field unit with smartphone Bluetooth interface was assembled and field-tested in three coastal deployment campaigns. The theoretical innovation centres on the aptamer multiplexing architecture enabling simultaneous tri-toxin detection from a single electrode. Keywords: biosensor, marine biotoxins, paralytic shellfish toxins, aptamer, Nigerian coastal monitoring.