Molecularly Encoded Rohitukine-Derived pH-Responsive Carbon Dots for Mercury Ion Sensing, Anticounterfeiting, and Live-Cell Imaging

The sustainable synthesis of multifunctional fluorescent nanomaterials from renewable molecular sources represents a promising direction in green nanoscience. Herein, we report a molecularly guided green synthesis of rohitukine-derived carbon dots (R-CDs) using the bioactive chromone alkaloid rohitukine as a structurally defined precursor, yielding ultrasmall carbonaceous nanostructures with intense and stable fluorescence. The rigid heterocyclic framework and intrinsic oxygen- and nitrogen-rich functionalities of rohitukine enable controlled carbonization and surface passivation, resulting in highly emissive, water-soluble carbon dots with encoded surface chemistry. The R-CDs exhibit reversible pH-dependent fluorescence over a wide range, enabling reliable pH sensing, and show selective mercury ion detection with a linear response from 5–25 μM and a detection limit of 0.30 μM, with minimal interference from competing metal ions. Owing to their excellent photostability and biocompatibility, the R-CDs display efficient cellular uptake and bright live-cell imaging performance, and further function as fluorescent inks for invisible-to-visible anticounterfeiting applications. This work establishes rohitukine as a drug-inspired natural product precursor for the sustainable design of multifunctional carbon nanomaterials with integrated environmental sensing, bioimaging, and security-related functionalities.