Green tea extract mediated biogenic synthesis of silver nanoparticles: Characterization, cytotoxicity evaluation and antibacterial activity

Silver nanoparticles (AgNPs) are widely used in biomedical fields because of their potent antimicrobial activity. Biogenic synthesis of nanoparticles has gained considerable attention due to its simplicity, low cost and absence of organic solvents. This work describes the one-pot one-minute biogenic synthesis of AgNPs with a commercial green tea extract (Camellia sinensis). The tea polyphenols acted as reducing and stabilizing agents for the nanoparticles. The surface of the biogenic AgNPs was further coated with polyethylene glycol (PEG) to enhance their dispersion and biocompatibility. The obtained nanoparticles were extensively characterized by ultraviolet-visible spectroscopy (UV–vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), electronic and atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering and inductively coupled plasma mass spectrometry (ICP-MS). The results demonstrated the formation of spherical nanoparticles of pure Ag° coated with tea polyphenols, at the nanoscale and with moderate polydispersity. The nanoparticles did not exhibit significant toxicity to human keratinocyte (HaCaT) cells. The antimicrobial efficacy of the biogenic nanoparticles was demonstrated against gram-positive Staphylococcus aureus (ATCC 29213), gram-negative Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 700603), Escherichia coli (ATCC 25922) and Salmonella enterica (ATCC 14028) bacterial strains. Salmonella enterica was found to be the most sensitive strain to the nanoparticles, with a minimum inhibitory concentration and minimum bactericidal concentration of 7 and 15 µg/mL, respectively. Interestingly, at the concentration range in which the AgNPs showed an antibacterial effect, they were not toxic to HaCaT mammalian cells. Thus, green tea synthesized AgNPs could find important biomedical applications in the combat of pathogenic bacteria with low cytotoxicity to normal cells.