Aptamer-Based Electrochemical Biosensors for Marine Toxins

Marine toxins are naturally occurring chemicals that can contaminate certain seafood. They are usually tasteless, odourless and have no toxic effect on shellfish. However, they exhibit toxicity towards marine mammals, birds, fish and humans. The ethical problems as well as the technical difficulties associated with the currently employed analysis methods for marine toxins are encouraging the research for suitable alternatives to be applied in a regulatory monitoring regime. Here, we report electrochemical biosensing platforms for okadiac acid (OA) as well as brevetoxin-2 (BTX-2) detection using aptamers as specific receptors. Using in vitro selection, high affinity DNA aptamers to OA and BTX-2 were successfully selected for the first time from a large pool of random sequences. The binding of the toxins to aptamer pools/clones was monitored using fluorescence and electrochemical impedance spectroscopy (EIS). Most of the selected aptamers exhibited high binding affinity to their target toxins with a dissociation constants in the nanomolar range. The effects of the incubation time, pH and metal ions concentrations on the aptamers-toxins binding were studied. The highest affinity aptamers were then used to construct label-free impedimetric biosensors for both OA and BTX-2 detection showing good sensitivity. A high degree of cross reactivity of the selected BTX aptamers to the two similar congeners, BTX-2 and BTX-3 was observed, whereas no cross reactivity to other marine toxins was obtained. Moreover, the aptasensors were applied for the detection of OA and BTX-2 in spiked shellfish extracts showing very good recovery percentages. We believe that the continual emergence of novel, high-affinity aptamers will open the way to a variety of biosensing architectures, particularly for small-molecule toxin detection in complex samples.