Discrimination of normal/cancer cells in bioimaging through a rolling circle amplification-enhanced red carbon dots-embedded multivalent aptamers nanoplatform.

Glutathione (GSH) is a key biomarker closely associated with cancer, and its content varies greatly between normal cells and cancer cells. However, intracellular detection of GSH was challenging because existing probes not only have a long detection time but also have fluorescence in the blue-green region that overlaps with the biological matrix's spontaneous fluorescence, thus affecting the detection accuracy. Therefore, a new red fluorescent nano-probe was needed to rapidly and accurately detected GSH within the biological matrix. Herein, red carbon dots (R-CDs) synthesized via hydrothermal method using N-(4-amino phenyl) acetamide and 4-Bromo-1,2-diaminobenzene as precursors offer enhanced fluorescence that could be quenched by MnO nanosheets (MnO NS) and restored by GSH. By combining R-CDs with the AS1411 aptamer and using rolling circle amplification, a multivalent aptamer modified R-CDs assembly (Assembly@R-CDs) was created for swift cancer cell targeting. Compared to monomeric aptamer, such multivalent aptamers exhibited higher affinity and selectivity, thereby enhancing the specificity and sensitivity of detection. After the fluorescence of the multivalent assembly was quenched by MnO NS (Assembly@R-CDs@MnO NS), it could be restored when targeting cancer cells, which could realize the distinction between normal cells and cancer cells. The experiment showed that 4T1 cancer cells took up more Assembly@R-CDs@MnO NS than L929 normal cells and generated stronger fluorescence, indicating the high selectivity for cancer cell detection. The potential of such nanosystem for tumor diagnosis combination therapy is promising, especially considering the embedding properties of anthracene drugs such as doxorubicin in DNA carriers.