‘Green’ approach for obtaining stable pectin-capped silver nanoparticles: Physico-chemical characterization and antibacterial activity

The development of environmentally friendly, non-toxic and cheap technology for synthesis of silver nanoparticles with desired properties is currently under intensive investigation because such materials show huge potential for numerous biomedical applications. In this paper, we propose the ‘green’ technique to obtain stable silver nanoparticles using reducing and stabilizing capacity of natural polysaccharide pectin. The relationship between physico-chemical characteristics of formed pectin-capped silver nanoparticles and type of used pectin, as well as synthesis conditions, has been determined. Pectin-Ag nanocomposites were produced via reduction of silver nitrate by pectin in alkaline medium at room temperature. The synthesized nanoparticles were characterized by ultraviolet-visible and Fourier-transform infrared spectroscopy, X-ray diffraction analysis, transmission electron microscopy and dynamic light scattering. It has been established that pectin-capped silver nanoparticles have a spherical shape with a mean diameter from 8 to 28 nm, a negative charge and an absorption maximum in the range from 401 to 412 nm, depending on the type of pectin constituent. Antibacterial activity of the free pectins and their nanocomposites with Ag0 was evaluated by diffusion and suspension methods against both gram-positive (Bacillus pumilus, Bacillus subtilis) and gram-negative (Escherichia coli) bacteria. The size and composition-dependent antibacterial activity of ‘green’ synthesized silver nanoparticles has been demonstrated. It has been shown that among the pectin varieties only amidated one displayed antibacterial action on Bacillus strains: the minimum inhibitory concentration (MIC) was 3.4–7.1 mg mL−1. It has been found that antibacterial activity of pectin-capped silver nanoparticles depended on the type of introduced pectin and its ratio. The synthesized nanoparticles exhibited significant antimicrobial activity toward gram-negative bacteria Escherichia coli (MIC 0.18-0.39 mM) as compared with gram-positive Bacillus bacteria (MIC 0.39–1.55 mM).