Electrochemical impedance sensor for herbicide alachlor based on imprinted polymer receptor

Abstract

Alachlor (ALA), a carcinogenic herbicide is detected in surface and groundwater, as well as in milk, eggs, and meat. So, the sensitive detection of ALA is essential for humans. To respond, we report a molecularly imprinted polymer (MIP) receptor for simple electrochemical sensing of ALA. The MIP film was immobilized onto glassy carbon electrode by electrodeposition of o‑phenylenediamine (o‑PD) in the presence of ALA as a template, followed by the ALA leaching out to create specific recognition cavities to ALA. The stepwise fabrication of the sensor was characterized by recording cyclic, square wave voltammetry peak currents and the electron transfer resistance (Ret) where the [Fe(CN)6]3−/4− was used as an electro-active probe. The mole ratio of ALA to o‑PD as well as the controlled release of the alachlor from the MIP‑o‑PD network was optimized to create a maximum number of free imprinted sites that affected the sensor sensitivity and its linear range. The increment in the Ret of the redox probe [Fe(CN)6]3−/4− upon selective recognition of ALA to the free cavities of MIP film is employed as the sensor response. At the optimal experimental conditions, the relative change in Ret is linearly correlated to the ALA concentrations in a range of 1 nM to 1 μM ALA. This sensor shows the high sensitivity of ALA with a limit of detection of 0.78 nM ALA. The affinity of MIP to ALA is proved by calculating the dissociation constant (Kd) in nM range. The high selectivity of the MIP sensor against the interferences propachlor and metalaxyl has been confirmed. Finally, the reliability of MIP-GCE for ALA detection is proved in tap water samples spiked by ALA. These findings indicate that such a sensor can be used for in-field measurements of other herbicides as a simple detection platform.