Green synthesis of silver and gold ultra nanocomposites from silk fibroin and their application for treatment of endodontic infections

The present study is designed to investigate the antibacterial efficacy of B. mori silk fibroin based silver and gold ultra bio-nanocomposites (SF-AgUNC and SF-AuUNC) against Enterococcus faecalis for endodontic disinfection. The SF-AgUNC and SF-AuUNC based irrigant solution was tested in- vitro against Enterococcus faecalis (ATCC: 29212). In this direction, SF-AgUNC and SF-AuUNC synthesized by silk fibroin are very important as they are economically cheap and easy to biosynthesize. The synthesis of SF-AgUNC and SF-AuUNC was accomplished by dissolving 1 mM silver nitrate and 0.5 mM auric chloride respectively in 10 ml of fibroin as precursors. The structural and morphological analysis was executed by UV-Vis Spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopic analysis (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS). The qualitative antimicrobial activity of SF-AgUNC and SF-AuUNC were performed against inoculum of Enterococcus faecalis containing 1⨯10⁵ CFU/ ml. The same solutions were tested on dentine specimens inoculated with bacterial cultures and found remarkable biofilm reduction. The structural and morphological analysis reveals the formation of SF-AgUNC and SF-AuUNC having quasi-spherical morphology. The average particle size for SF-AgUNC and SF-AuUNC was same (~ 8 nm). The XRD study confirms that, both SF-AgUNC and SF-AuUNC were crystalline in nature. The bacterial growth inhibition and significant biofilm reduction was observed on dentine specimens treated with SF-AgUNC, SF-AuUNC and positive control. In antibacterial study, at 30 μg/well concentration of SF-AgUNC and SF-AuUNC, 3.13 ± 0.22 and 1.13 ± 0.22 cm of zone of inhibition was noted respectively. Moreover, growth of Enterococcus faecalis was completely inhibited at 20 μg/ml and 30 μg/ml when treated with SF-AgUNC and SF-AuUNC respectively. Hence, the present study concludes that SF-AgUNC and SF-AuUNC can be used as an effective intracanal medicament for the treatment of dental problems with no cyto toxicity.