Green synthesis of silk sericin-embedded silver nanoparticles and their antibacterial application against multidrug-resistant pathogens.

Abstract

Background: The green synthesis strategy of metallic nanoparticles (NPs) has become popular due to being environmentally friendly. Stable silver nanoparticles (AgNPs) have been synthesized by natural products such as starch, soy protein, various extract of leaves, barks, and roots functioning both as reducing and stabilizing agents. Likewise, silk sericin (SS) is a globular protein discarded in the silk factory might be used for NP synthesis. In this research, we focus on the green synthesis and stabilization of AgNPs by SS as well as assessment of their antibacterial activities against some drug-resistant pathogen.

Results: SS was extracted from Bombyx mori silkworm cocoons in an aqueous medium. 17 w/w% of dry sericin powder with respect to the cocoon's weight was obtained by freeze-drying. Furthermore, AgNPs conjugated to sericin, i.e., SS-capped silver nanoparticles (SS-AgNPs) were synthesized by easy, cost-effective, and environment-friendly methods. The synthesized SS-AgNPs were characterized by UV-visible spectroscopy, Fourier-transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction measurement. It has been found from the absorbance of UV-visible spectroscopy that a higher percent of SS-AgNPs was obtained at a higher concentration of silver nitrate solution. FTIR-ATR spectra showed that the carboxylate groups obtained from silk sericin act as a reducing agent for the synthesis of silver nanoparticles, while NH₂+ and COO- act as a stabilizer of AgNPs. The X-ray diffractogram of SS-AgNPs was quite different from AgNO₃ and sericin due to a change in the crystal structure. The diameter of AgNPs was around 20-70 nm observed using TEM. The synthesized SS-AgNPs exhibited strong antibacterial activity against multidrug-resistant pathogens, Escherichia coli and Pseudomonas aeruginosa. Minimal inhibitory/bactericidal concentrations against E. coli and P. aeruginosa were 20μg/mL.

Conclusions: This study encourages the use of Bombyx mori for the ecofriendly synthesis of SS-AgNPs to control multidrug-resistant microorganisms.