An electrochemical sensor modified with poly(3,4-ethylenedioxythiophene)-wrapped multi-walled carbon nanotubes for enzyme inhibition-based determination of organophosphates

We report on an acetylcholinesterase (AChE) based sensor for the determination of organophosphates (OPs). A nanocomposite consisting of poly(3,4-ethylenedioxythiophene) (PEDOT; a conducting polymer) and functionalized multi-walled carbon nanotubes (f-MWCNTs) was used as a host matrix for covalent immobilization of AChE. The unique properties of PEDOT and f-MWCNTs proved to be highly efficient for retaining the activity and stability of AChE. The effects of pH value of the phosphate buffer, concentration of enzyme, substrate concentration and incubation time were optimized using chlorpyrifos-methyl as a model OP as it exerts a strong inhibitory effect on AChE. Differential pulse voltammetry (DPV) analysis performed at +0.15 V revealed a linear relation of current in respect to chlorpyrifos-methyl concentration range (0.001 to 50 ppb) with 0.001 ppb as a detection limit. The sensor can be regenerated to 97% of its activity by applying 2-pyridine aldoxime methiodide (2-PAM) as a regenerating agent. It can be re-used up to six times and stored up to one month. The sensor was applied to the determination of chlorpyrifos-methyl in spiked lettuce where it gave recoveries ranging between 95 and 97%.