Acetylcholinesterase-Free Colorimetric Detection of Chlorpyrifos in Fruit Juice Based on the Oxidation Reaction of H2O2 with Chlorpyrifos and ABTS2− Catalyzed by Hemin/G-Quadruplex DNAzyme

Herein, we for the first time report an acetylcholinesterase (AChE)-free colorimetric method for the detection of chlorpyrifos (CP), which is based on the oxidation reaction of H 2 O 2 with CP and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS 2− ) catalyzed by hemin/G-quadruplex DNAzyme. In the absence of CP, ABTS 2− is directly oxidized by H 2 O 2 with hemin/G-quadruplex DNAzyme as a biocatalyst to produce the blue-green-colored free radical anion (ABTS ·− ), accompanied with an obvious UV-visible absorbance at 418 nm. However, the amount of H 2 O 2 used in H 2 O 2 -DNAzyme-ABTS 2− system will be decreased if CP is first reacted with H 2 O 2 , leading to the decrease of the amount of ABTS ·− and a change in the UV-visible absorbance of ABTS ·− at 418 nm. Thus, an indirect dependence relation between CP concentration and the absorbance of ABTS ·− at 418 nm could be constructed and used for CP detection. Under optimal conditions, the detection range of the method is 0.04–1 μg/mL, with a detection limit of 0.01 μg/mL. Application of the method in real juice samples shows good analytical features in terms of recoveries (95–107.5 %), the relative standard deviation (RSD) (0.6–4.7 %), rendering it as an attractive candidate to current methodologies for the determination of CP.