Porphyrin/Graphene Based Electrochemical Nanosensors for the Detection of Nerve Agent Simulant Dimethyl Methylphosphonate (DMMP)

Abstract

Dimethyl methylphosphonate (DMMP) a nerve agent simulant was electrochemically detected in aqueous media by reduced graphene oxide (RGO)/tetraphenylporphyrin (TPP), RGO/zinc tetraphenylporphyrin (Zn-TPP), RGO/5,10,15,20-tetrakis(para-nitrophenyl)porphyrin (TNPP), RGO/5,10,15,20-tetrakis(para-aminophenyl)porphyrin (TAPP) composites modified electrode in a ratio (1:0.5, 1:1, 1:2), similar studies were performed for the pristine graphene (PG)/porphyrins modified electrode. Nanocomposites were prepared through noncovalent pipi stacking interactions between graphene and porphyrin materials. The characterization of prepared materials was done by Fourier transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), nuclear magnetic resonance spectroscopy (1H NMR), and energy dispersive x-rays spectroscopy (EDX). Also, the electrochemical studies were performed for analyte (DMMP) by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Furthermore, effect of electron withdrawing (NO2) and electron donating (NH2) substituents was observed on porphyrin ring system for electrochemical analysis of DMMP. RGO/TAPP nanocomposite modified electrode presented least peak current response than RGO/TNPP and RGO/TPP, whereas RGO/TNPP showed enhanced current signal than RGO/TPP nanocomposite modified electrode. Moreover, RGO/Zn-TPP (1:2) nanocomposite modified electrode presented optimum peak current response than all other prepared electrodes. RGO/Zn-TPP/GCE (1:2) was used to check the effect of variable scan rate (10-210 mVs-1), pH (4-8) and concentration (100-900 μM). Thus, increase in anodic and cathodic peak current response was observed at high scan rate and with the increase in concentration of DMMP upto 900 μM. Also, the best results were obtained at pH 6 for the electrochemical analysis of DMMP. Selectivity studies were carried out at RGO/Zn-TPP (1:2) modified electrode for DMMP and glyphosate through CV. RGO/Zn-TPP (1:2) nanocomposite modified electrode showed large linear response range (100-900 μM), good electrocatalytic activity, low detection limit (0.25 μM), excellent sensitivity (0.90 μA μM-1 cm-2), good selectivity, stability, repeatability and reproducibility towards DMMP.