来源：ACS Publications
The present work focuses on methotrexate (MTX)-conjugated terbium-doped carbon dots (CDTb) as an innovative drug delivery platform for targeted colon cancer therapy using Caco-2 cell lines. Briefly, carbon dots (CDs) were synthesized via a microwave-assisted method, subsequently doped with terbium using a chemical precipitation method, and then conjugated with MTX drug molecules. The physicochemical properties of the synthesized CDTb-MTX complexes were evaluated using various characterization methods, namely, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, dynamic light scattering, UV–visible spectrophotometry, and steady-state and fluorescence lifetime measurements. XPS analysis verified the elemental composition and chemical states of C, N, O, and Tb, confirming Tb3+ coordination with surface oxygen functionalities and successful MTX surface functionalization. HR-TEM analysis revealed that the developed CDTb and MTX-conjugated CDTb nanoparticles were spherical, with mean diameters of 3.174 ± 0.492 nm and 6.22 ± 0.89 nm, respectively. ζ-potential analysis revealed a surface charge shift from −19.7 mV for CDTb to +1.1 mV for CDTb-MTX, confirming surface modification and improved cellular interaction. Fluorescence studies showed quenching of the fluorescence emission of CDTb nanoparticles in the presence of MTX, indicating successful and efficient conjugation of MTX onto the CDTb surfaces. The quantum yield of CDTb was 57.4%, accompanied by a fourfold increase in lifetime (8.79 ns) compared to bare CDs, making it suitable for bioimaging applications. Fluorescence quenching and Stern–Volmer analysis (Ksv = 2.11 × 106 M–1) confirmed a static interaction between CDTb and MTX. The drug adsorption and release rate of MTX was 98.42% at 8 h and 85.23% at 24 h, respectively. Hemolysis investigation revealed that the CDTb nanoparticles are biocompatible, even at higher concentrations (3.42% at 4 mg mL–1). In vitro studies demonstrated that CDTb nanoparticles did not induce toxicity in L929 cells and enhanced cell proliferation at low concentrations. Notably, the CDTb-MTX complex showed greater cytotoxicity against colon cancer (Caco-2) cells compared to free MTX. The cytotoxic effects of the CDTb-MTX complex induced cell death in Caco-2 cells, as evaluated by flow cytometry. In brief, this multifunctional theranostic drug model using CDTb-MTX could enhance the site-specific drug targeting against colon cancer cell lines.