Development of a third-generation biosensor to determine sterigmatocystin mycotoxin: An early warning system to...

A third-generation enzymatic biosensor was developed to quantify sterigmatocystin (STEH). It was based on a glassy carbon electrode modified with a composite of the soybean peroxidase enzyme (SPE) and chemically reduced graphene oxide. The optimal conditions to construct the biosensor were obtained through an experimental design based on the response surfaces methodology. The experiments were performed in 0.1 mol L^-1 phosphate buffer solution, pH 5. Amperometric measurements were carried out at - 0.09 V vs Ag/AgCl (3 mol L^-1 NaCl). The biosensor showed a lineal response in the concentration range from 6.9 × 10^-9 to 5.0 × 10^-7 mol L^-1. The limit of detection was 2.3 × 10^-9 mol L^-1 for a signal: noise ratio of 3: 1. Values of the apparent Michaellis-Menten constant, K_M^app, obtained by using both Lineweaver-Burk and Eadi-Hofstee methods were (1.5 ± 0.2) × 10^-6 and (1.2 ± 0.2) × 10^-6 mol L^-1, respectively. STEH was analyzed in corn samples spiked with STEH, with an average recovery of 96.5%. The biosensor was also used to determine STEH in corn samples inoculated with the Aspergillus flavus fungus, which is an aflatoxins producer. Considering that STEH is a precursor of aflatoxin B₁ (AFB₁) in its biological transformation, its decrease over time was related to the production of AFB₁. The STEH concentration determined using the biosensor was in very good agreement with that determined by HPLC.