A γ-Fe2O3/thiophene-sulfur-doped graphene nanozymes-based colorimetric sensor for visual and quantitative determination of chlorpyrifos

The development of an innovative peroxidase mimic is crucial for achieving accurate and low-cost naked-eye detection for pesticide residues in agricultural products. Herein, a visual sensor for chlorpyrifos was engineered by employing γ-Fe 2 O 3 /thiophene-sulfur-doped graphene (γ-Fe 2 O 3 /t-SG) magnetic nanocomposite as an artificial nanozyme . The γ-Fe 2 O 3 /t-SG magnetic nanocomposite with single–crystalline structure was fabricated by a facile thermal-treatment strategy by controlling the annealing temperature between graphene oxide (GO) and ferric sulfate. Significantly, the resulting γ-Fe 2 O 3 /t-SG magnetic nanocomposite revealed the markable peroxidase-like activity toward 3,3,5,5-tetramethyl benzidine oxidation (TMB). A novel colorimetric method for the rapid detection of chlorpyrifos was developed based on the high enzyme-like activity of γ-Fe 2 O 3 /t-SG magnetic nanocomposite and the inhibition of acetylcholinesterase activity by chlorpyrifos. This colorimetric sensor demonstrated excellent performance in chlorpyrifos quantification, with a linear range from 0.5 to 1000 μg mL −1 and a detection limit of 0.17 μg mL −1 (S/N = 3). The stability, ease of separation, and high peroxidase-like catalytic activity of γ-Fe 2 O 3 /t-SG magnetic nanocomposite makes it as an ideal candidate for a wide range of potential applications as peroxidase mimetics.