Electrochemical biosensing strategy for highly sensitive pesticide assay based on mercury ion-mediated DNA conformational switch coupled with signal amplification by hybridization chain reaction

Abstract

Pesticides are of significant importance in agricultural fields, but the pesticide residues are considered to be strong hazards to the environment and human health. Motivated by the urgent demand for sensitive pesticide assay, this study addresses the need by reporting a new electrochemical biosensing platform for pesticide detection, which is relied on acetylcholinesterase (AChE)-catalyzed hydrolysis product-triggered Hg2+ release coupled with subsequent hybridization chain reaction (HCR) for signal amplification. The hydrolysis product thiocholine (TCh) can interact with Hg2+ embedded in the stem of hairpin structured helper DNA probe to switch its conformation to single-stranded DNA (ssDNA). The ssDNA then triggers the HCR between two hairpin probes and yields long double-stranded DNA, which can capture numerous methylene blue molecules, thus generating a remarkably amplified electrochemical signal. In the presence of pesticides, AChE activity is inhibited and the amount of generated TCh decreases, eventually resulting in the decrease of electrochemical signal. It has been found that the as-proposed approach shows a linear relationship between the peak current and the logarithm of the pesticide concentration. A directly measured detection limit of 10μg/L is achieved by using aldicarb as a model analyte. Furthermore, this method exhibits good applicability for aldicarb detection in real samples. It is also versatile for the detection of other carbamate and organophosphate pesticides that have inhibition effect on AChE activity. Therefore, the proposed method shows great potential for practical application in food safety fields and will provide alternative approaches for the detection of pesticide residues.