An“on-off-on” reversible fluorescent probe based on nitrogen-doped carbon dots derived from Mahonia fortunei: Sequential detection of Pb2+ and L-histidine and construction of an implication molecular logic gate

Biomass-derived B-CDs were synthesized from Mahonia fortunei fruits. • The B-CDs showed bright blue emission with a quantum yield of 31.1%. • Pb 2+ selectively quenched B-CD fluorescence with a low LOD of 26 nM. • L-Histidine restored fluorescence via competitive Pb 2+ coordination. • An IMPLICATION logic gate was constructed from the on–off–on response. Nitrogen-doped carbon dots (B-CDs) with deep-blue fluorescence were synthesized through a one-step hydrothermal route using the fruits of the medicinal plant Mahonia fortunei as the biomass carbon source and 1-naphthylamine as the nitrogen dopant. The resulting B-CDs showed excitation-independent emission, a high fluorescence quantum yield of 31.1%, and excellent resistance to salt, photobleaching, and long-term storage. Pb 2+ efficiently quenched B-CD fluorescence by forming non-emissive ground-state complexes through bidentate coordination with oxygen- and nitrogen-containing surface groups, switching the probe to the “off” state. By contrast, L-histidine (L-His), whose imidazole group has stronger competitive affinity for Pb 2+ , dissociated the carbon dot‑lead complexes and markedly restored fluorescence, returning the system to the “on” state. The platform afforded a detection limit of 26 nM for Pb 2+ , while the L-His-induced fluorescence recovery response was linear over 40–80 μM, with an average fluorescence recovery efficiency of 88.2%. On the basis of this reversible fluorescence response, an IMPLICATION molecular logic gate was constructed using Pb 2+ and L-His as chemical inputs and fluorescence intensity as the output, enabling logic discrimination in a two-component system. UV–vis absorption spectroscopy, time-resolved fluorescence lifetime analysis, and FT-IR spectroscopy jointly supported the reversible “on-off-on” response mechanism. This work provides a practical strategy for developing natural plant-derived carbon-dot platforms for reversible fluorescence sensing and molecular logic devices. Download: Download high-res image (155KB) Download: Download full-size image