Electrochemical Detection of Nitrite Ions Using Gold Nanoparticles Supported on Multiwalled Carbon Nanotube/Reduced Graphene Oxide Composites

Developing efficient electrochemical sensors for nitrite detection is crucial due to its toxicity and widespread presence in food and water. Engineered carbon-based supports significantly enhance the electrocatalytic activity of noble metal composites by tailoring surface area, nanoparticle dispersion, and electron-transfer pathways. In this study, we synthesized gold nanoparticles (AuNPs) supported on carboxylated multiwalled carbon nanotube (c-MWCNT) and reduced graphene oxide (rGO) composites (Au/c-MWCNT/rGO) via solution plasma sputtering to fabricate advanced electrochemical sensing materials for nitrite detection. To optimize their electrocatalytic performance, the mass ratios of c-MWCNT to rGO were systematically varied at 0:1, 1:4, 1:2, 1:1, and 1:0. The resulting AuNPs were highly crystalline and uniformly dispersed throughout the carbon supports, with average diameters ranging from 6.4 ± 3.1 to 14.5 ± 7.7 nm. Electrochemical nitrite detection was evaluated in phosphate-buffered saline using a three-electrode system, with a glassy carbon modified by Au/c-MWCNT/rGO composites. Differential pulse voltammetry revealed well-defined linear calibration curves for nitrite detection. Among all samples, the Au/c-MWCNT/rGO(1:1) composite exhibited the highest sensitivity, with two distinct linear response ranges (0.05 μM–1 mM and 1–10 mM) and a low detection limit of 1.0 μM. This superior performance is attributed to an optimal balance between the high electrical conductivity of c-MWCNT and the large specific surface area of rGO, which enabled uniform AuNP distribution, reduced particle size, and optimal loading density. This structural synergistic integration facilitated efficient electron transfer and enhanced nitrite adsorption. Furthermore, the fabricated sensor exhibited excellent repeatability, high selectivity, and reliable recovery in real water sample analysis.