Chapter 18 - Applications of biogenic silver nanocrystals or nanoparticles as bactericide and fungicide

Abstract

Silver nanocrystals or nanoparticles (NPs) are synthesized from an array of biogenic sources such as plant leaves, roots, and stems, seeds; tree gum; bacteria; fungi; algae; and biomolecules. Biogenic sources are preferred compared with chemical synthesis because of their renewability, low cost, nontoxicity, biodegradability, biocompatibility, the tunable size and shape of nanocrystals, and their dual ability to function as reductant and stabilizer molecules. Biogenic silver (Ag) NPs are characterized by different analytical instrumentation techniques such as UV-visible absorption spectroscopy, transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Biogenic Ag NPs exhibit biocidal activity against various bacteria and fungi and thus function as bactericides and fungicides. They are protein-capped and show enhanced stability toward elevated temperatures variations in pH and storage conditions, and superior antibacterial action. The antibacterial and antifungal action of Ag NP is extensively studied against different environmental bacteria, human pathogens, plant pathogens, and so on utilizing various in vitro and in vivo methodologies. This review provides briefly discusses the biogenic synthesis of Ag NPs and their characterization and gives detailed information about their functionality as bactericides and fungicides against various microbes. The mechanism of antibacterial action is schematically exemplified via membrane damage and reactive oxygen species production. Furthermore, promising antimicrobial applications of Ag NPs in various industrial and consumer sectors such as water purification, textiles, food packaging, wound dressing are mentioned. Further studies are needed on consumer acceptance and the effect of residual Ag NPs on various biota in the food chain in terms of cytotoxicity and genotoxicity.