Double-enzymes-mediated Fe2+/Fe3+ conversion as magnetic relaxation switch for pesticide residues sensing

It is a great challenge to develop a newly rapid and accurate detection method for pesticide residues. In this work, based on acetylcholinesterase (AChE) and choline oxidase (CHO), a double-enzymes-mediated Fe2+/Fe3+ conversion as magnetic relaxation switch was explored for the measurement of acetamiprid residue. In the double-enzymes reactions, acetylcholine chloride (ACh) can be catalyzed to produce choline by AChE, which is successively hydrolyzed to betaine and hydrogen peroxide (H2O2) by CHO. According to the enzyme inhibition principle, AChE activity will be inactivated in the presence of acetamiprid, thus leading to the less production of H2O2. Wherein, Fe2+, ACh, AChE and CHO were optimized as the reaction substrates. In the reaction system, acetamiprid can be reflected by the transverse relaxation time (T2) that related with H2O2 mediated Fe2+ variations, which was further developed as an enzyme cascade amplification method. The detection linear range is 0.01∼1000 μg mL−1 (R2 = 0.99), and the limit of detection (LOD) is 2.66 ng mL−1 (S/N = 3, n = 3), behaving a 335-fold improvement in LOD than that of traditional enzyme inhibition method (0.89 μg mL−1). This method can realize “one-step mixing” detection of acetamiprid, which makes it a promising analytical tool for monitoring pesticide residue in complicated samples.