Luminescent heparin-functionalized carbon dots with potential applications in nanoparticle-protein interactions and cell imaging

In this study, we report the synthesis and comprehensive characterization of heparin-capped carbon dots (Hep-C-dots) prepared using D-glucose as a carbon precursor and heparin, a negatively charged polysaccharide belonging to the glycosaminoglycan family, as a capping and stabilizing agent. The obtained Hep-C-dots exhibited a uniform nanoscale size distribution with an average diameter of 2.5 ± 0.5 nm and a high negative surface charge (− 36.8 mV). Full characterization of as-synthesized Hep-C-dots has been done by several state-of-the-art analytical techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and zeta potential analysis. The interactions between Hep-C-dots and key human proteins, namely human methemoglobin (HB) and human serum albumin (HSA), were investigated via fluorescence spectroscopy, demonstrating significant binding affinities with K_sv values of 2.61 ± 0.5 × 10⁷ M^− 1 for HSA and 1.83 ± 0.4 × 10⁷ M^− 1 for HB. Cytotoxicity assays performed on A549 lung cancer cells revealed that Hep-C-dots exhibit slightly higher toxicity compared to bare carbon dots (C-dots), with IC₅₀ values of 176.21 µg/mL and 200.4 µg/mL, respectively. Moreover, hemolysis assessment using bovine red blood cells (RBCs) showed that Hep-C-dots induce negligible hemolysis (0.002% at 200 µg/mL), confirming their excellent hemocompatibility. These findings suggest that Hep-C-dots hold promise as biocompatible nanomaterials for biomedical applications.