Sensing of Ponceau 4R dye by fluorescence of carbon quantum dots synthesized by electrical flash

Ponceau 4R is a widely used synthetic azo food dye, and excessive consumption has raised health concerns, highlighting the need for rapid and affordable monitoring methods in food and beverages. In this study, we synthesized carbon quantum dots (CQDs) for the first time using an electrical flash method and demonstrated their application as a fluorescence-based probe for Ponceau 4R detection. The electrical flash method produced CQDs from glucose through a rapid, solvent-free, one-step process that is both eco-friendly and cost-effective. Structural and spectroscopic analyses—including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), photoluminescence measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible (UV–Vis)—confirmed the formation of graphitic CQD nanostructures. These structures have a crystallite size of 9 nm and possess surface functional groups that ensure stable aqueous dispersibility and strong photoluminescence (PL) with an optical quantum yield of 35.7%. Ponceau 4R efficiently quenched CQD photoluminescence, enabling quantitative detection across a linear concentration range of 0–4000 ng/mL, with a limit of detection (LOD) of 300 ng/mL. Temperature-dependent analysis and a fitted non-linear model of quenching versus concentration indicated a static quenching mechanism that arises from dye physisorption onto the surface of the CQDs, with an enthalpy change of − 48.6 kJ/mol. To improve accessibility, we developed a low-cost portable sensing platform that requires only a smartphone and approximately $7 in accessories, comparable to conventional photoluminescence instrumentation. This work introduces a scalable and environmentally benign CQDs synthesis strategy and provides a low-cost, portable proof-of-concept platform for monitoring Ponceau 4R in food-related applications.