Label-free okadaic acid detection using growth of gold nanoparticles in sensor gaps as a conductive tag

Okadaic acid (OA) is a marine toxin ingested by shellfish. In this work, a simple, sensitive and label-free gap-based electrical competitive bioassay has been developed for this biotoxin detection. The gap-electrical biosensor is constructed by modifying interdigitated microelectrodes with gold nanoparticles (AuNPs) and using the self-catalytic growth of AuNPs as conductive bridges. In this development, the AuNPs growth is realized in the solution of glucose and chloroauric acid, with glucose oxidation used as the catalysis for growth of the AuNPs. The catalytic reaction product H₂O₂ in turn reduces chloroauric acid to make the AuNPs grow. The conductance signal amplification is directly determined by the growth efficiency of AuNPs and closely related to the catalytic activity of AuNPs upon their interaction with OA molecule and OA aptamer. In the absence of OA molecule, the OA aptamer can absorb onto the surfaces of AuNPs due to electrostatic interaction, and the catalytically active sites of AuNPs are fully blocked. Thus the AuNPs growth would not happen. In contrast, the presence of OA molecule can hinder the interaction of OA aptamer and AuNPs. Then the AuNPs sites are exposed and the catalytic growth induces the conductance signal change. The results demonstrated that developed biosensor was able to specifically respond to OA ranging from 5 ppb to 80 ppb, providing limit of detection of 1 ppb. The strategy is confirmed to be effective for OA detection, which indicates the label-free OA biosensor has great potential to offer promising alternatives to the traditional analytical and immunological methods for OA detection.