Moringa oleifera mediated MnO2 electrochemical sensor for ammonia detection in aqueous medium

Abstract

The development of metal oxide-based electrochemical sensors are simple to use, portable, and affordable with excellent performance, stability, and sensitivity for the precise detection of targeted analytes in food safety has received a lot of interest as a result of advancement trends in recent studies. In this work, Moringa leaf extract-MnO₂ nanoparticles (M-MnO₂)-based sensors have been developed as an ultra-sensitive ammonia indicator for detecting food spoilage. M-MnO₂ nanoparticles of a sensing material were prepared by hydrothermal method. The crystal structure, morphology, elemental composition, elemental mapping, functional bond, surface area, pore size was confirmed by Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Analysis (EDAX), Fourier transform infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and Nitrogen adsorption–desorption isotherm (BET analysis). The M-MnO₂ was dropped onto a glassy carbon electrode using a drop casting technique and was used as a working electrode in an electrochemical sensor for ammonia detection. An electrochemical approach using a Moringa leaf extract-MnO₂ sensor is examined using cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and linear sweep voltammetry (LSV). The differential pulse voltammetry analysis of sensing provided a superior response for the anodic peak current has a linear correlation with ammonia concentrations ranging from 1 to 5 µM. The maximum current response was obtained at the optimized potential range between − 100 mV and 500 mV at pH = 12 with the scan rate of 35 mV/s. The electrochemical sensing probe demonstrated a strong linear correlation between the concentration of ammonia and current with corresponding limit of detection (LOD) and quantification (LOQ) of 0.76 µM and 2.33 µM with correlation coefficient R² is 0.99, and a sensing probe sensitivity of 128.6907 μA/μM/cm². The stability of the fabricated sensor was tested for a week and achieved a satisfactory result with an error of 0.2%. Ammonia oxidation peak current, the modified electrode displayed exceptional electrocatalytic characteristics. Analytical parameters such as linearity, sensitivity, and stability are also investigated. Consequently, the experimental analysis of the M-MnO₂ nanoparticle sensor confirmed that it is a promising material for determining ammonia for food safety.