One-Step Synthesis of Size-Tunable Gold@Sulfur-Doped Graphene Quantum Dot Nanocomposites for Highly Selective and Sensitive Detection of Nanomolar 4-Nitrophenol in Aqueous Solutions with Complex Matrix

In this study, a simple one-step synthesis procedure for the fabrication of a gold nanoparticle (Au NP)@sulfur-doped graphene quantum dot (Au@S-GQD) with tunable size was developed for the sensitive and selective detection of 4-nitrophenol in water and wastewater with a complex matrix. The particle size of two to six layered S-GQD is in the range of 1–7 nm with a mean diameter of 4.0 ± 0.5 nm. The S-GQD serves as a reducing agent for both Au ions and 4-nitrophenol reduction to generate Au@S-GQD nanocomposites as well as to produce the absorption signal of 4-aminophenol at 307 nm. The particle size of Au@S-GQD is tunable by simply adjusting the Au precursor concentration, and the mean diameter increases from 5 to 25 nm when the Au precursor concentration increases from 50 to 200 μM. Moreover, the Au@S-GQD nanocomposite exhibits good UV–visible absorption properties, and the change of wavelength ratio between 307 and the SPR peak of Au at 530 nm (A307/A530) is used to detect nanomolar levels of 4-nitrophenol after the interaction of 4-nitrophenol with S-GQD by π–π stacking interaction. A wide dynamic range of 4 orders of magnitude with a limit of detection (LOD) of 3.5 nM in deionized water is achieved. The UV–visible response of Au@S-GQD also shows good selectivity to 4-nitrophenol detection over other aromatic and nitroarene compounds. In addition, the Au@S-GQD sensing platform is successfully applied to the detection of 0.05–50 μM 4-nitrophenol in highly contaminated food wastewater with an LOD of 8.4 nM. The recovery of 0.1–20 μM 4-nitrophenol in three different aqueous solutions with a complex matrix is in the range of 97 ± 2 to 110 ± 3%. Results obtained clearly indicate the superiority of using Au@S-GQD as the optical sensing probe for the detection of nano- to micromolar levels of 4-nitrophneols in aqueous solutions, which can be developed as a high performance and robust sensing platform for rapid detection of nitroaromatics in a wide variety of water and wastewater.