Deoxynivalenol (DON) is a mycotoxin that is produced by the Fusarium genus and is widely found in cereal grains such as wheat and corn. Sodium metabisulphite (SMBS) is a promising feed additive in swine farming to mitigate the negative impact caused by DON on animal growth. Here we report on an advanced electrochemical sensor based on fluorinated reduced graphene oxide modified with gold nanoparticles (Au/F-rGO) for the rapid detection and monitoring of SMBS. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the morphology and composition of the prepared Au/F-rGO nanocomposites. Cyclic voltammetry, linear sweep voltammetry, and differential pulse voltammetry were utilized to investigate the electrochemical performance of the Au/F-rGO sensor. Our study showed that the optimized Au/F-rGO nanocomposite exhibited a wide linear range of responses, a low detection limit, high sensitivity, and high stability for the detection of SMBS. When tested in simulated digestive fluids (e.g., salivary fluid and gastric fluid), high selectivity of the sensor for SMBS detection was demonstrated, showing promise for practical applications.