Polydopamine Coating of Graphitic Carbon Nitride, g-C₃N₄, Improves Biomedical Application

Graphitic carbon nitride (g-C₃N₄) is an intriguing nanomaterial that exhibits photoconductive fluorescence properties under UV-visible light. Dopamine (DA) coating of g-C₃N₄ prepared from melamine was accomplished via self-polymerization of DA as polydopamine (PDA). The g-C₃N₄ was coated with PDA 1, 3, and 5 times repeatedly as (PDA@g-C₃N₄) in tris buffer at pH 8.5. As the number of PDA coatings was increased on g-C₃N₄, the peak intensity at 1512 cm^-1 for N-H bending increased. In addition, the increased weight loss values of PDA@g-C₃N₄ structures at 600 °C from TGA thermograms confirmed that the coating was accomplished. The band gap of g-C₃N₄, 2.72 eV, was reduced to 0.87 eV after five coatings with PDA. A pristine g-C₃N₄ was found to have an isoelectric point (IEP) of 4.0, whereas the isoelectric points of 1PDA@g-C₃N₄ and 3PDA@g-C₃N₄ are close to each other at 3.94 and 3.91, respectively. On the other hand, the IEP of 5PDA@g-C₃N₄ was determined at pH 5.75 assuming complete coating with g-C₃N₄. The biocompatibility of g-C₃N₄ and PDA@g-C₃N₄ against L929 fibroblast cell lines revealed that all PDA@g-C₃N₄ coatings were found to be biocompatible up to a 1000 mg/mL concentration, establishing that PDA coatings did not adversely affect the biocompatibility of the composite materials. In addition, PDA@g-C₃N₄ was screened for antioxidant potential via total phenol content (TPC) and total flavonoid content assays and it was found that PDA@g-C₃N₄ has recognizable TPC values and increased linearly with an increased number of PDA coatings. Furthermore, blood compatibility of pristine g-C₃N₄ is enhanced considerably upon PDA coating, affirmed by hemolysis and the blood clotting index%. Additionally, α-glucosidase inhibitory properties of PDA@g-C₃N₄ structures revealed that 67.6 + 9.8% of this enzyme was evenly inhibited by 3PDA@g-C₃N₄ structure.