Development of an amperometric enzyme electrode biosensor for sterigmatocystin detection

A simple, rapid and highly sensitive electrochemical biosensor for the detection of sterigmatocystin (ST) based on a new enzyme named aflatoxin-oxidase (AFO), which was cloned from Armillariella tabescens and expressed in Pichia pastoris, was developed. The enzyme was immobilized onto chitosan-single-walled carbon nanotubes (CS-SWCNTs) modified Au electrode via electrostatic interactions and hydrophobic interactions. The fabricated procedures of the biosensor were characterized with Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and electrochemical techniques. Effects of some experimental variables such as pH, applied potential, and temperature on the response of the biosensor were investigated. The CS-SWCNTs nanocomposite matrix could provide a favorable microenvironment for AFO to realize the direct electron transfer on the underlying electrode. The enzymatic electrode exhibited an excellent electrocatalytic response to ST, long-term stability, and good reproducibility. The linear range of ST determination was from 10 to 1480 ng mL−1 with a detection limit of 3 ng mL−1 based on the signal-to-noise ratio of 3. The kinetic parameters such as α (charge transfer coefficient), Ks (electron transfer rate constant), image (the apparent Michaelis–Menten constant), and Ea (activity energy) were evaluated to be 0.4, 0.9 ± 0.02 s−1, 7.8 μM and 38.8 kJ mol−1, respectively.