Green synthesis of carbon nanodots for direct and rapid determination of theophylline through fluorescence turn on–off strategy

Main conclusion Carbon dots (CDs) have attracted more and more attention due to their low toxicity, good biocompatibility and easy preparation. However, synthesis of CDs with high quantum yield using green and economic method is still challenging. Herein, an effective synthesis route was reported for green synthesizing CDs using waste chicken eggshell membrane as carbon source via microwave-assisted method. The obtained CDs showed good photo-stability with a high quantum yield of 19.5%. The as-prepared CDs was designed as a fluorescent probe for facile, rapid, sensitive determination of theophylline (TP) based on the fluorescence turn on–off strategy. The designed method exhibited good performance for the determination of TP. Under the optimal conditions, the fluorescent response of CDs was proportional to the TP concentrations in the range of 0.1–1 and 1–1000 μM with limit of detection of 28 nM. Moreover, the proposed method was applied to detect the TP content in tea samples. The as-prepared CDs provide a green and economic approach for the food safety test. Graphical abstract Eggshell membrane-derived carbon nanodots for direct and rapid detection of theophylline.