Abstract
Generally, limited research is extended in studying stability and applicational properties of silver nanoparticles (Ag NPs) synthesized by adopting ‘green chemistry’ protocol. In this work, we report on the synthesis of stable Ag NPs using plant-derived materials such as leaf extract of Neem (Azadirachta indica) and biopolymer pectin from apple peel. In addition, the applicational properties of Ag NPs such as surface-enhanced Raman scattering (SERS) and antibacterial efficiencies were also investigated. As-synthesized nanoparticles (NPs) were characterized using various instrumentation techniques. Both the plant materials (leaf extract and biopolymer) favored the synthesis of well-defined NPs capped with biomaterials. The NPs were spherical in shape with an average particle size between 14-27 nm. These bio-NPs exhibited colloidal stability in most of the suspended solutions such as water, electrolyte solutions (NaCl; NaNO3), biological solution (bovine serum albumin), and in different pH solutions (pH 7; 9) for a reasonable time period of 120 hrs. Both the bio-NPs were observed to be SERS active through displaying intrinsic SERS signals of the Raman probe molecule (Nile blue A). The NPs were effective against the Escherichia coli bacterium when tested in nutrient broth and agar medium. Scanning and high-resolution transmission electron microscopy (SEM and HRTEM) images confirmed cellular membrane damage of nanoparticle treated E. coli cells. These environmental friendly template Ag NPs can be used as an antimicrobial agent and also for SERS based analytical applications.
Highlights
Metallic silver nanoparticles (Ag NPs) have gathered much attention due to their unique properties, which depend on their morphology, dimension and colloidal stability
The average hydrodynamic diameter (HDD) values for A. indica and pectin Ag NPs measured in water by DLS differed from their average diameters measured by TEM and were observed to be 33.42 and 199.2 nm (Table 1), respectively
One inherent limitation of the DLS method is taken into account; since the particle size is correlated with the scattered light intensity, presence of fewer larger diameter or aggregated NPs will dominate the intensity [15]
Summary
Metallic silver nanoparticles (Ag NPs) have gathered much attention due to their unique properties, which depend on their morphology, dimension and colloidal stability. Colloidal stability of the nanoparticles (NPs) in solvent other than water is desired in most of the biological applications and in several other analytical applications [1]. Unstable nanoparticle (NP) aggregates may significantly contribute to dissolution of ions from NPs [4], which increases during particle storage [5]. Such coexistence of the NP and its ionic forms may induce toxic pathway [6,7]. It is essential to synthesis stable NPs, which can minimize ion dissolution and retain its physicochemical properties
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