Parallel detection of okadaic acid and saxitoxin in mussels with an electrochemical aptamer-based assay

Phycotoxins are highly toxic compounds bioaccumulating in marine organisms, thus seriously affecting human health. Two electrochemical aptasensors for parallel detection of okadaic acid (OA) and saxitoxin (STX), exploiting a competitive strategy, are then proposed in this study. Screen-printed electrochemical cells were modified first by the electrodeposition of gold nanoparticles and then by the electropolymerization of poly(aniline-co-anthranilic acid) copolymer or poly(l-lysine) film. A conjugate between bovine serum albumin and each phycotoxin was immobilized covalently on the polymeric film and competed with the free phycotoxin in solution for the binding with a specific biotinylated aptamer. The competition was traced with an enzymatic conjugate between streptavidin and alkaline phosphatase: upon addition of 1-naphthyl phosphate, the enzymatic conversion of the substrate occurred. Differential pulse voltammetry (DPV) measurements were carried out to detect the enzymatic product 1-naphthol. A signal-off response was retrieved with detection limits of 66.4 pg/mL for OA and 7.9 pg/mL for STX, respectively. The aptasensors were also tested in the analysis of real mussel samples and their performance was compared with those of commercial enzyme-linked immunosorbent assays. The developed sensing strategy offers an efficient approach for monitoring OA and STX in seafood, thus representing a significant step towards ensuring consumer safety.