Green Synthesis, Characterization and Antibacterial Activities of Silk Sericin Capped Zinc Oxide Nanoparticles

Abstract

In recent years, interest in metal-based antibacterial materials has increased due to microorganisms gaining resistance to antibiotics. Silk sericin obtained from Bombyx mori cocoon has found use in many different areas thanks to its biocompatibility, hydrophilic character and biodegradability. Zinc oxide nanoparticles (ZnONPs) obtained in various zinc salts exhibit broad-spectrum antibacterial properties. In this study, to be produce metal based antibacterial materials, synthesis of silk sericin-coated ZnONPs (SS-ZnONPs) in a green and scalable method was investigated by using silk sericin protein as both reducing and capping agent to obtain ZnONPs. For producing SS-ZnONPs, 2% silk sericin solution was mixed with Zn(NO3)2 solution and the blend solution was heated at 100 °C for a certain period of time. Observing surface plasmon resonance (SPR) peak specific at 380 nm in the UV-vis spectrum of SS-ZnONPs represented the formation of ZnONPs. Then, the chemical, morphological, crystalline, thermal, and antibacterial properties of the synthesized SS-ZnONPs were examined. Characteristic peak of the Zn-O band was found in fourier transform infrared spectroscopy (FTIR) analysis of SS-ZnONPs. According to scanning electron microscopy (SEM) analyses, ZnONPs had morphology similar to cubic/hexagonal shape, showed a uniform structure, and did not represent any agglomerations. In energy dispersive spectroscopy (EDS) analyses of SS-ZnONPs, peaks belonging to carbon, nitrogen, oxygen, sulphur, and zinc elements were observed. The formation of Zn peak indicated that the zinc ions were transformed into ZnONPs. In addition, characteristic peaks of zinc were seen in the X-ray diffractometer (XRD) result of SS-ZnONPs. Thermogravimetric analysis (TGA) showed that the thermal stability and remaining amount of SS-ZnONPs was higher compared to pure silk sericin powder due to the formation of ZnONPs. Lastly, agar well diffusion test was carried out with Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 25922) bacteria and SS-ZnONPs showed antibacterial action against S. aureus. It has been observed that the obtained SS-ZnONPs can be used as antibacterial agents. However, it was also understood that the ZnONPs concentration in this study was low for high antibacterial activity.