Colorimetric biosensor for the assay of paraoxon in environmental water samples based on the iodine-starch color reaction

•The iodine-starch color reaction was applied for colorimetric assay of paraoxon.•The assay of paraoxon can be performed in homogenous solution without reagent synthesis and enzyme immobilization.•A colorimetric assay for paraoxon was achieved with a limit of detection 4.7 ppb.•This biosensor has the potential of on-site assay of OPs residues in environmental samples.

In this work, a new colorimetric biosensor for the assay of paraoxon was developed via the conventional iodine-starch color reaction and multi-enzyme cascade catalytic reactions. In the presence of acetylcholine chloride, acetylcholinesterase (AChE) and choline oxidase (ChO) catalyzed the formation of H2O2, which then activated horseradish peroxidase (HRP) to catalyze the oxidation of KI to produce an iodine-starch color reaction. Upon exposure to paraoxon, the catalytic activity of AChE was inhibited and less H2O2 generated, resulting in a decrease in the production of I2 and a drop in the intensity of solution color. This colorimetric biosensor showed high sensitivity for the assay of paraoxon with a limit of detection 4.7 ppb and was applied for the assay of paraoxon in spiked real samples. By employing the conventional iodine-starch color reaction, this biosensor has the potential of on-site assay of OPs residues in environmental samples.

Graphical abstractIn the presence of acetylcholine chloride, the enzymes acetylcholinesterase (AChE) and choline oxidase (ChO) catalyzed the formation of H2O2, which then activated horseradish peroxidase (HRP) to catalyze the oxidation of KI to produce an iodine-starch color reaction. Upon exposure to paraoxon, the catalytic activity of AChE was inhibited and less H2O2 generated, resulting in a decrease in the production of I2 and a drop in the intensity of the color of the solution. By employing the conventional iodine-starch color reaction, this biosensor has the potential of on-site assay of OPs residues in environmental samples.Download high-res image (133KB)Download full-size image