Objective To screen for the most effective antimicrobial carbon dots from the traditional Chinese medicines Baiji (Bletilla striata), Cili (Rosa roxburghii), Lingzhi (Ganoderma lucidum) and Tianma (Gastrodia elata), and to systematically investigate the physicochemical properties, photothermal performance, antibacterial activity and mechanism of manganese-doped G. lucidum carbon dots (Mn-GLCDs). Methods Four kinds of herbal carbon dots derived from B. striata, R. roxburghii, G. lucidum and G. elata were prepared by a conventional hydrothermal method. The carbon dots with optimal antibacterial activity were screened out, and the morphology, structure and in vitro photothermal performance of the manganese-doped carbon dots were characterized. The antibacterial performance against Staphylococcus aureus and Escherichia coli under near-infrared (NIR) irradiation was evaluated through zone of inhibition assays, bacterial co-culture experiments, and biofilm inhibition and disruption tests. The antibacterial mechanism was preliminarily investigated by intracellular active oxygen fluorescence detection using a DCFH-DA probe. Biosafety was assessed by hemolysis assay and cytotoxicity test. Intracellular reactive oxygen species (ROS) fluorescence measurement using the 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) probe was adopted to preliminarily elucidate its antibacterial mechanism. Hemolysis assays and cytotoxicity evaluations were conducted to verify their biological safety. Results GLCDs possessed remarkably stronger antibacterial activity than carbon dots prepared from B. striata, R. roxburghii and G. elata carbon dots. Mn-GLCDs had a particle size of approximately 5 nm, and their surfaces were rich in hydrophilic functional groups including -OH, -NH₂, C=O, C-N-C and C-O-C. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS) confirmed that the mass fraction of Mn²⁺ reached 0.83%, and Mn²⁺ was stably present in the carbon dot framework in a coordinated form. The red shift of the UV-Vis absorption peak and the Raman I_D/I_G > 1 indicated that Mn²⁺ doping narrowed the bandgap and increased the density of structural defects. Photothermal performance evaluation showed that Mn-GLCDs could rapidly heat up under 808 nm laser irradiation (1.5 W/cm²), with a photothermal conversion efficiency of 35.03%. The maximum temperature fluctuation in six cycles of heating-cooling stability test was less than 6%, indicating good photothermal stability. Fluorescence performance test showed a fluorescence quantum yield of 20.51% and excitation-dependent fluorescence emission. In vitro antibacterial experiments demonstrated that, compared with undoped G. lucidum carbon dots, Mn-GLCDs exhibited the strongest antibacterial effect against S. aureus and E. coli under near-infrared irradiation, and could significantly inhibit and disrupt bacterial biofilms. Intracellular active oxygen detection showed that upon near-infrared irradiation, Mn-GLCDs elevated the active oxygen levels in S. aureus and E. coli to 6.75-fold and 5.44-fold of the negative control group, respectively. Biosafety evaluation showed that the hemolysis rate of Mn-GLCDs was below 5% within the antibacterial concentration range, and Mn-GLCDs exhibited no obvious toxicity to L929 and RAW264.7 cells. Conclusion This study constructs for the first time Mn-GLCDs, which significantly enhance the photothermal conversion capability and antibacterial activity. The mechanism is related to the induction of intracellular active oxygen. This work provides an experimental basis for the development of novel traditional Chinese medicine-based nanoscale antibacterial agents.

traditional Chinese medicines  /  Ganoderma lucidum (Leyss. ex Fr.) Karst.  /  carbon quantum dots  /  manganese ion doping  /  photothermal properties  /  bacterial biofilms  /  Bletilla striata (Thunb.) Reichb. f.  /  Rosa roxburghii Tratt.  /  Gastrodia elata Bl.  /  antibacterial activity  /  Staphylococcus aureus  /  Escherichia coli  /  hemolysis  /  cytotoxicity  /  biological safety