Selective redox-responsive theragnosis nanocarrier for breast tumor cells mediated by MnO₂/fluorescent carbon nanogel

A redox-responsive fluorescent carbon nanogel (FCN) was designed as a bioimaging probe for targeted drug delivery to cancer cells. FCN was synthesized by the carbonization of disulfide cross-linked hyaluronic acid in the fluorescence "on" mode, followed by the attachment of manganese oxide (MnO₂) nanosheets for fluorescence quenching (fluorescence "off"). We hypothesized that the fluorescence intensity of paclitaxel (PTX)-MnO₂/FCN would suddenly increase (fluorescence "on") in the presence of a high level of glutathione (GSH) in cancer cells, owing to the reduction of MnO₂ to Mn²⁺ and cleavage of the disulfide bond. Consequently, PTX would be released from the FCN system. Consistent with this hypothesis, the designed system recovered FCN fluorescence and triggered drug release through the cleavage of the disulfide bond by GSH. Moreover, PTX-MnO₂/FCN demonstrated stable fluorescence intensity after GSH treatment, serving as a potential biosensor. PTX-MnO₂/FCN exhibited excellent biocompatibility with normal cells and selectively targeted tumor cells, highlighting the therapeutic capabilities of this system. The developed PTX-MnO₂/FCN structure may serve as a smart drug delivery system with diagnostic and therapeutic properties, good selectivity, and compatibility, and with excellent potential for biomedical applications.