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

Abstract 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 H 2 O 2 , 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 H 2 O 2 generated, resulting in a decrease in the production of I 2 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.