Giovanna Aita and Young Hwan Moon
Audubon Sugar Institute, Louisiana State University Agricultural Center, St. Gabriel, LA, USA; gaita@agcenter.lsu.edu
Nanoparticles are less than 100 nm in size, and those made from metals such as silver have sparked considerable interest as ideal materials due to their unique features, such as biocompatibility, inert nature, stability, and low toxicity. Silver nanoparticles (AgNPs) are used in the medical and non-medical fields, as antimicrobial substances, catalysts, drug delivery carriers, and cosmetic ingredients, as well as plant growth bio-stimulants, environmental, and remediation agents. The reducing and capping potential of polyphenols extracted from bagasse was investigated in the green synthesis of AgNPs without the external addition of reducing agents. The reddish-brown color formation and peak appearance at 430 nm were indications of the successful synthesis of the AgNPs. The AgNPs and reducing biomolecules were further characterized by microscopy (scanning electron microscopy (SEM), transmission electron microscopy (TEM)) and spectroscopy techniques (energy-disperse X-ray spectroscopy (EDS), Fourier transform infrared- attenuated total reflectance (FTIR-ATR), X-ray diffraction (XRD)), indicating nanoparticles of spherical shape, with particle sizes averaging ~15 nm and surface charge of -24.8 mV. The antimicrobial activity of the synthesized nanoparticles was evaluated against several microbial species, Listeria monocytogenes ATCC 19115, Staphylococcus aureus ATCC 12600, Salmonella enterica ATCC 13312, Pseudomonas syringae ATCC BAA 871, Escherichia coli ATCC 35218, and two strains isolated from sugarcane crusher juice, Leuconostoc mesenteroides (A17) and Leuconostoc pseudomesenteroides (A25). The synthesized nanoparticles showed strong biocidal activity against the bacteria, which was further confirmed by microscopy techniques. The cell and nanoparticles are interacting with the cell surface of microorganisms, penetrating the cell, and causing the disruption of intracellular organelles. These nanoparticles also prevented the growth of microbial biofilms. A biofilm is a complex and functional community of microbes encased in a primarily polysaccharide matrix, which acts as a barrier to protect microbes against most antimicrobials.