Background: Nanotechnology has become an essential and important
field tool to develop various kinds of nanoparticles with high surface area to volume
ratios and unique properties. Therefore, nanoparticles have been utilized for
several biomedical applications; including diagnostics, drug delivery, biomarkers,
and distinct antibacterial, antifungal and anti-biofilm agents. Silver nanoparticles
(AgNPs) are known to be effective antibacterial agents and exhibit strong cytotoxicity
against a broad range of microorganisms compared to conventional usage of
silver salt and silver metal. The aim of this study was to synthesize graphene oxide-
silver nanoparticle nanocomposites using a novel biomolecule called pepsin.
Methods: The synthesized graphene oxide (GO) silver nanoparticle nanocomposite
(GO–AgNPs) was characterized by ultraviolet-visible absorption spectroscopy, X-ray diffraction,
scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The antibacterial
and anti-biofilm activity of synthesized nanocomposite was evaluated using various assays,
such as cell growth, cell viability, and reactive oxygen species generation.
Results: The graphene oxide (GO)-silver nanoparticle nanocomposite (GO–AgNPs) was synthesized
in the presence of AgNO3 and pepsin. The synthesized GO–AgNPs were characterized by various
analytical techniques. The AgNPs were distributed uniformly on the surface of graphene oxide with
an average size of 20 nm. Antibacterial activities of GO–AgNPs were evaluated by cell viability and
anti-biofilm assay. GO, AgNPs and GO-AgNPs nanocomposites showed significant antibacterial
activity against Shigella flexneri and Streptococcus pneumoniae. The loss of viability was observed
in S. flexneri and S. pneumonia decreased in a dose- and time-dependent manner. GO-AgNPs
showed significantly higher production of reactive oxygen species (ROS) compared to GO, AgNPs
and the control, which is a possible mechanism of cell death. N-acetyl cysteine (NAC) significantly
prevented cell death induced by GO, AgNPs, GO-AgNPs from oxidative stress in Shigella flexneri
and Streptococcus pneumoniae via decreasing ROS generation. It suggests that elevated ROS is responsible
for the loss of cell viability.
Conclusion: Pepsin mediated GO–AgNPs could facilitate the simple, easy approach for large-scale
production of graphene-based nanocomposites; GO–AgNPs exhibited an efficient and significant
inhibitor for cell viability compared to GO, and silver nanoparticles. The nanocomposites could be
effective antibacterial agents for the treatment of various infectious diseases.