Ratiometric electrochemical quantitation of methyl parathion based on NiHCF/PDDA@rGO nanocomposites

This work presents an on-off ratiometric electrochemical quantitation study of methyl parathion (MP), one of the most popularly used organophosphorus pesticides, based on electrode modification with a newly developed nanocomposite, i.e., reduced graphene oxide (rGO) functionalized with poly(diallyldimethylammonium chloride) (PDDA) and nickel hexacyanoferrate (NiHCF). It was shown that MP strongly adsorbs on the modified electrodes and produces a distinct reduction signal (-NO 2 ), which increases proportionally with its concentration; meanwhile, the intrinsic reduction signal (Fe(III)/(II)) from the nanocomposite (NiHCF/PDDA@rGO) decreases due to the inhibited electron-transfer process upon MP binding. Indeed, plotting the ratiometric signal (the ratio of decreased Fe(III)/(II) current and the increased MP current) as a function of the analyte (MP) concentration produces a linear calibration curve in the range of 0.05 μM to 10 μM (R 2  = 0.9987), with a limit of detection (LOD) of 16 nM. The method was further validated in real water samples, showing recoveries of 96.2–102% with relative standard deviations below 3.3%, which are comparable with standard HPLC results.