Methotrexate-loaded manganese nitrogen dual-doped carbon quantum dots as targeted nano drug-delivery system for potential use in cancer theranostics

The present work highlights manganese nitrogen dual-doped carbon quantum dots as a novel pH-sensitive drug delivery system, for the delivery of methotrexate, targeted to cancer cells, along with the simultaneous real-time monitoring of cellular uptake and drug delivery using fluorescence imaging. Briefly, methotrexate was conjugated with the as-prepared quantum dots to form a nano drug-delivery system through non-covalent interactions. The developed material demonstrated drug loading efficiency of similar to 91 % and a very efficient (similar to 80 %) pHresponsive drug release at pH 5.5. The cytotoxic properties of the developed nano-platform viz. manganese, nitrogen dual-doped carbon quantum dots, and methotrexate conjugated manganese nitrogen dual-doped carbon quantum dot complex were evaluated in cancer cells (HeLa) and healthy human cells (L929). The conjugated complex demonstrated excellent biocompatibility, high cellular uptake, and a substantial drug release. Healthy human cells were largely unaffected when incubated with both the MTX-conjugated Mn-, N-CQD and the free drug. Additionally, in vitro, the fluorescence bio-imaging potential of the developed nano-platform was also assessed, where the unconjugated (free) quantum dots exhibited better blue fluorescence imaging potential compared to that of the conjugated complex, which can be attributed to fluorescence quenching due to the presence of methotrexate. This study highlights the manganese nitrogen dual-doped carbon quantum dots capable of pH-responsive methotrexate drug delivery selective to cancer cells. The combination of drug delivery and fluorescence imaging creates an efficient platform for targeted therapy, allowing very precise drug release while accessing non-invasive monitoring of therapeutic response. This method holds a great promise for advancing cancer treatment strategies, with the potential for increased efficacy and decreased side effects.