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Red emitting carbon dots with phosphorus and manganese dopants were explored for synergistic in vitro fluorescence/MR imaging and cytoprotective effects.

In this work, manganese‐doped carbon quantum dots (Mn‐CQDs) have been synthesized through a one‐pot hydrothermal method by using waste green tea. The Mn2+ dopants were introduced to impart magnetic resonance capability. Upon optimization of the experimental conditions, magnetofluorescent Mn‐CQDs exhibit an excitation‐dependent blue emission. The abundant functional groups on Mn‐CQDs not only promote water solubility but also allow straightforward functionalization with amine groups. The amine‐terminated Mn‐CQDs were then subsequently conjugated to folic acid (FA) and chlorin e6 (Ce6) to obtain the Mn‐CQDs@FA/Ce6 magnetofluorescent photodynamic therapy (PDT) agent. in vitro studies using three different cells indicated specific targeting of Mn‐CQDs@FA/Ce6 to the overexpressing folate receptor human epithelial carcinoma cell line (HeLa) cancer cells. Furthermore, Mn‐CQDs@FA/Ce6 enhanced magnetic resonance imaging (MRI) signal with an r2/r1 ratio of 5.77. Favorably, by using the Mn‐CQDs@FA delivery system, active Ce6 can reach the cellular interior while its red fluorescence (FL) and reactive oxygen species generation can be retained, as has been verified by confocal microscopy. in vitro cell viability studies verified the biocompatibility of Mn‐CQDs@FA/Ce6 nanohybrid with no significant toxicity up to 500 ppm while PDT treatment with 5 min irradiation (671 nm, 1 W cm−2) was effective in killing >90% of cells. The light‐triggered Mn‐CQDs@FA/Ce6 multifunctional hybrid can serve as a dual‐modal FL/MRI probe and as an efficient PDT agent to detect and eradicate cancer cells remotely.

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