A versatile dual-excitation carbon dots for simultaneous detection and discrimination of flavonoids in dietary and herbal sources

Flavonoids, widely recognized for their health benefits, are commonly consumed through plant-based diets. However, excessive intake of these bioactive compounds may pose significant health risks. Thus, reliable detection methods for assessing their safety are urgently required. In this work, an innovative ratiometric fluorescence method based on dual-excitation carbon dots (DE-CDs) is proposed for the simultaneous detection and discrimination of flavonoids, including quercetin, rutin, morin and kaempferol. The ratiometric signal, derived from the intensity ratio of two excitations at a fixed emission wavelength, exhibits a correlated change in response to varying flavonoid concentrations. As a proof of feasibility, quercetin is selected as a model analyte, achieving a broad linear range of 0.075–50 μM with a low detection limit of 75 nM. Furthermore, the absorption bands of flavonoids and the excitation spectrum of DE-CDs display differential spectral superposition, leading to variations in the internal filtration effect efficiency, thus enabling the discrimination of different flavonoids even in mixed samples. Additionally, to enhance practical applicability, a smartphone-assisted sensing device is designed by incorporating a DE-CDs-embedded polyvinyl alcohol film, which successfully detects flavonoids via RGB analysis and provides satisfactory recovery rates in real-sample assays. Collectively, this study not only establishes a sensitive excitation-encoded ratiometric fluorescence approach for the detection and specific discrimination of flavonoids but also demonstrates its potential for on-site applications through integration with smartphone technology.