Doxorubicin-Conjugated Terbium-Doped Carbon Dots for Site-Specific Colon Cancer Theranostics

This work focuses on synthesizing fluorescent rare earth terbium-doped carbon dots (CD-Tb) as a nanodrug carrier for doxorubicin (DOX) drug moieties using the hydrothermal method. The nature of CD-Tb nanoparticles in the absence and presence of DOX was evaluated using various spectroscopic and microscopic techniques, namely, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), Zeta potential analyzer, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–visible, fluorescence emission, and lifetime spectroscopy. The synthesized CD-Tb nanoparticles were found to be approximately 7 nm in size and spherical, with a surface charge of −20.7 mV. They are biocompatible with electron-rich amino groups on their surface and are used for the bioconjugation of DOX, an anticancer drug. The photophysical characterization shows 92.5% of adsorption and 89% of in vitro release of DOX from CD-Tb nanoparticles. This might be due to the presence of carboxyl and amino groups on the DOX surface and CD-Tb nanoparticles. The effective concentration of CD-Tb nanoparticles and DOX was achieved at a stoichiometric ratio of 1:1.5. Further, the Stern–Volmer quenching rate constant (K_q) of CD-Tb-DOX was calculated as 4.9 × 10¹⁰ L/mol·s^–1, and the binding of nanoparticles with various concentrations of DOX is found to be static. In addition, the in vitro antitumoral activity of free DOX and the CD-Tb-DOX against Caco-2 cancer cell lines (human colon cancer) and L929 cell lines (mouse fibroblast cells) was evaluated as the healthy cell model. CD-Tb-DOX’s in vitro cytotoxic evaluation result shows higher cytotoxicity and morphological changes at Caco-2 colon cancer tumor sites than free DOX. In brief, this study confirms that the synthesized CD-Tb-DOX nanocarriers could significantly enhance the metabolic damage in the Caco-2 cancer cell lines (human colon cancer) and facilitate the action of cellular apoptosis, which might be helpful in site-specific targeting drug delivery applications.