An electrochemical sensor based on carboxymethylated dextran modified gold surface for ochratoxin A analysis

A disposable electrochemical immunosensor method was developed for ochratoxin A analysis to be applied for wine samples by using a screen-printed gold working electrode with carbon counter and silver/silver chloride pseudo-reference electrode. An indirect competitive enzyme-linked immunosorbent assay (ELISA) format was constructed by immobilising ochratoxin A conjugate using passive adsorption or covalent immobilisation via amine coupling to a carboxymethylated dextran (CMD) hydrogel on the gold working electrode. Electrochemical detection was performed using 3,3′,5,5′-tetramethylbenzidine dihyrochloride (TMB) and hydrogen peroxide with horse radish peroxidase (HRP) as the enzyme label. Chronoamperometry at −150 mV vs. onboard screen-printed Ag–AgCl pseudo-reference electrode was then used to detect the generated signal. The performance of the assay and the sensor was optimised and characterised in pure buffer conditions before applying to wine samples. The resulting immunosensor for ochratoxin A in buffer achieved a limit of detection of 0.5 μg L−1 with a linear dynamic detection range of 0.1–10 μg L−1 for passive adsorption of the toxin conjugate. While for covalent immobilisation through CMD-modified gold electrode, a limit of detection of 0.05 μg L−1 was achieved with a linear dynamic detection range of 0.01–100 μg L−1. The CMD-modified gold immunosensor was then evaluated in spiked and affinity purified wine samples achieving a detection limit comparable to buffer solutions (0.05 μg L−1).