Acetylcholinesterase-catalyzed silver deposition for ultrasensitive electrochemical biosensing of organophosphorus pesticides

Herein, an electrochemical biosensing platform with acetylcholinesterase (AChE)-catalyzed silver deposition was developed for the ultrasensitive detection of organophosphorus pesticides (OPs). The biosensing mechanism is based on the fact that AChE can catalyze the rapid hydrolysis of indoxyl acetate to form hydroxyindole, which in turn reduces silver ions to metallic silver, resulting in the deposition of silver on the gold electrode. Upon sweeping positive voltages on the gold electrode using linear sweep voltammetry (LSV), the deposited silver on the gold electrode surface undergoes a rapid electrochemical oxidation reaction. Due to its lower oxidation potential under facile conditions with a relatively sharp peak, a small amount of deposited silver generated from AChE-catalysis could result in a significant change in the LSV response. In the presence of OPs, the AChE-catalyzed hydrolysis of indoxyl acetate is blocked, and then the silver deposition on the gold electrode declines, leading to a remarkable decrease in the LSV response and, thus producing a large signal output for the ultrasensitive detection of chlorpyrifos, a proof-of-concept OP in this work. The change in the LSV peak current intensity is linearly correlated with the logarithmic value of the chlorpyrifos concentration ranging from 10 pM to 10 nM with a low detection limit of 4.0 pM. To the best of our knowledge, this is the first example of a biosensing platform for ultrasensitive OP assay using AChE-controlled silver deposition to enhance the output of electronic signals.