Abstract: In this study, novel fluorescent carbon dots (CDs) were rapidly synthesized via a one-step hydrothermal method using 1,8-naphthalic anhydride (NA) and 1,2-phenylenediamine (OPD) as precursors. By optimizing reaction conditions, yellow fluorescent carbon dots (Y3-CDs) with superior luminescence performance were successfully prepared. The particle sizes and morphology of the Y3-CDs were characterized by high-resolution transmission electron microscopy (HR-TEM), revealing an average diameter of approximately 2.6 nm and an interlayer spacing of 0.21 nm. This spacing corresponds to the d-spacing of graphene (100) planes and is consistent with the diffraction peak observed at 42.88o in X-ray powder diffraction (XRD) analysis. X-ray photoelectron spectroscopy (XPS) confirmed the presence of sp2/sp3 hybridized carbons (C=C/C—C, 284.8 eV), carbon-nitrogen bonds (C—N, 286.5 eV), and carbonyl carbons (C=O, 288.4 eV). The optical properties of the Y3-CDs were further investigated using fluorescence spectrometry (FL), ultraviolet-visible absorption spectroscopy (UV-vis), and lifetime measurements. The fluorescence spectra exhibited non-excitation-dependent emission behavior, indicating a single emission center. Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) provided detailed structural insights. Due to their high purity, the characteristic hydrogen (H) and carbon (C) atoms could be clearly resolved and analyzed. 1H NMR results demonstrated that all H atoms were located on the surface of the carbon core, exhibiting ortho-substitution patterns and coupling effects. 13C NMR and DEPT 135 spectra confirmed the presence of ten distinct tertiary carbon atoms. The cell-tracking and imaging performance of Y3-CDs were systematically evaluated. Results demonstrated that Y3-CDs possess excellent cell imaging capabilities and anti-photobleaching properties. Even after 180 minutes of continuous irradiation, Y3-CDs retained strong fluorescence, enabling long-term tracking of HeLa cells. Co-localization experiments further highlighted their selective lipid droplet imaging ability, with a Pearson’s correlation coefficient of 0.846.

Key words: Carbon dots, NMR analysis, Anti-photobleaching, Cell tracking, Lipid droplet imaging