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/Gquadruplex DNAzyme as a biocatalyst to produce the bluegreen-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 UVvisible 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.
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