Developing a novel sensitive visual screening card for rapid detection of pesticide residues in food

A novel sensitive visual screening card for rapid detection of pesticide residues was developed based on the blue-green color intensity changes, which were generated as a result of indoxyl acetate hydrolysis catalyzed by acetylcholinesterase (AChE) and the inhibition of AChE activity by pesticides. The procedure for preparing the test card was optimized. The AChE was immobilized onto the Hybond N+ nylon membrane using physical adsorption method. The immobilization temperature was set at 4 °C and the immobilization time was set to 30 min. The immobilized enzyme was freeze dried under vacuum conditions for 2 min. The indoxyl acetate was dissolved in methanol and diluted to 10 mM by phosphate buffer solution (pH7.5). The inhibition time and the color development time were set to 15 min and 10 min respectively. The final experimental results on determining various pesticides showed that the limit of detection (LOD) of this assay system was 1 μg/mL for omethoate, 0.1 μg/mL for dichlorvos, 2 μg/mL for methamidophos, 0.05 μg/mL for chlorpyrifos, 1.5 μg/mL for carbaryl, and 0.8 μg/mL for pirimicarb. Detection results of pesticide residues in real food samples of fruit juices and vegetable showed this visual screening card had high sensitivity, good reproducibility and stable-storage property, suggesting its great potential for practical application in rapid determination of pesticide residues.