The Physicochemical and Antifungal Properties of Eco-friendly Silver Nanoparticles Synthesized by Psidium guajava Leaf Extract in the Comparison With Tamarindus indica

Harnessing nature for dual action: silver nanoparticles synthesized from guava leaf extract for photocatalytic degradation of methyl red and antibacterial applications

This study revealed novel insights into key parameters affecting the biogenic synthesis of silver nanoparticles (AgNPs) with a dual-faceted application via a green route utilizing aqueous guava (Psidium guajava L.) leaf extract as both a reducing and stabilizing agent. The formation of AgNPs was visually confirmed by a color change of the reaction mixture from pale yellow to reddish-brown. Characterization of the synthesized AgNPs revealed a surface plasmon resonance band at 415-420 nm in the Ultraviolet-Visible (UV-Vis) spectra, confirming the presence of AgNPs. Dynamic light scattering (DLS) analysis indicated an average particle size of approximately 29 nm, while X-ray diffraction (XRD) analysis confirmed the crystalline nature and high purity of the synthesized AgNPs. Transmission electron microscopy (TEM) images displayed a primarily spherical morphology with an average size of about 12 nm. Fourier transform infrared (FTIR) spectroscopic analysis further supported the role of phytochemicals, such as phenolic acids and flavonoids, in the bioreduction and stabilization of the AgNPs. The synthesized AgNPs exhibited significant antibacterial activity against Gram-positive (S. aureus, E. faecalis) and Gram-negative (P. aeruginosa) bacterial strains, as demonstrated by the disc diffusion method. Furthermore, the AgNPs demonstrated promising photocatalytic activity, achieving approximately 95-96% degradation of methyl red (MR) within 72 hours under sunlight exposure. The dual functionality of the as-synthesized AgNPs opens up exciting avenues in both environmental remediation and biomedical fields.

Fundamental Understanding of Bio-Nano Interface of Lysozyme on Psidium guajava Polyphenol Coated Silver Nanoparticles: Mechanistic Insights into the Effect of Protein Corona on the Antibacterial Efficacy

Recent times have witnessed revolutionary progress in the design and development of functionalized nanomaterials as promising tools for biomedicinal applications. However, the gap in the fundamental understanding of the "biological responses" of the nanomaterials after the formation of "protein-corona" when it is exposed to the body system has drawn a thin line from its discoveries to real clinical trial. In this article we have synthesized two different silver NPs capped with the polyphenols of Psidium guajava (guava) leaf extract and the other with one of its major polyphenolic groups, morin. Then, the formation of "bio-nano interface" of these synthesized AgNPs were illustrated in detail by taking the model carrier protein hen egg white lysozyme (HEWL). The formation of protein corona of HEWL on the surface of the AgNPs was revealed by the increase in the hydrodynamic size and the negative ξ-potential values as well as from the visualization of an ∼1 nm thick light gray layer of HEWL in the TEM micrographs. The binding interaction of surface adsorbed HEWL with the AgNPs was analyzed with various photophysical and molecular dynamics simulation (MD) techniques. HEWL interacted with these polyphenol-assisted AgNPs with moderate binding affinity (Kb ∼ 104 M-1) in a spontaneous manner with the structural integrity in its native conformation. Though several covalent forces are responsible for protein-NP interaction, electrostatic and hydrophobic forces of attraction played the major role in the complexation of HEWL with Guava L.-AgNPs and Morin-AgNPs, respectively. The lysozyme protein-corona on the synthesized polyphenol-assisted AgNPs altered their biological response as revealed from the reduction of antibacterial activity against pathological Gram-positive (E. faecalis) as well as Gram-negative (E. coli) bacterial strains in vitro.

Dose-dependent biological toxicity of green synthesized silver nanoparticles in rat's brain

Metal nanoparticles, in general, and silver nanoparticles (AgNPs), in particular, have been the focus of numerous studies over the last two decades. Recently, the green synthesis of metal nanoparticles has been favored over chemical synthesis due to its low toxicity and easy preparation. The present study aims to investigate the dose-dependent toxicity of green synthesized AgNPs on rats' brains. Thirty-four Wistar male rats were divided into four groups. The first, second, and third groups were administered for 14 days with three different doses (0.5, 5, and 10 mg/kg) of AgNPs, respectively. The fourth group, which served as a control group, was given normal saline for the same period. The toxicity of the green synthesized AgNPs on the cortical and hippocampal levels of the oxidative stress markers (MDA, NO, and GSH) as well as the activity of acetylcholinesterase (AchE) and the monoamine neurotransmitters (DA, NE, and 5H-T) were investigated. AgNPs showed minimal oxidative stress in the cortex and hippocampus for the administered doses. However, AgNPs showed an inhibitory effect on AchE activity in a dose-dependent manner and a decrease in the 5H-T and NE levels. The green synthesized AgNPs showed an ultrastructural change in the cellular membranes of the neurons. The green synthesis of AgNPs has reduced their cytotoxic oxidative effects due to their capping with biologically compatible and boosting molecules such as flavonoids. However, another neurotoxicity was observed in a dose-dependent manner.

UV-Light Mediated Biosynthesis of Silver Nanowires; Characterization, Dye Degradation Potential and Kinetic Studies

Herrin, a simple and eco-friendly method for the synthesis of silver nanowires (Ag-NWs) has been reported. Silver nanowires were synthesized using Psidium guajava seed extract that acted as a reducing agent as well as a stabilizing agent for silver nitrate solution. Synthesis was carried out at 50 °C temperature under continuous UV-irradiation. Silver nanowires were initially characterized by a UV-visible and FTIR spectrophotometer. In addition, morphology and particle size of synthesized Ag-NWs were determined using Field Emission Scanning Electron Microscopy and X-ray diffraction (XRD) techniques. Nanowires were found to have 12.8 μm length and 200–500 nm diameter and cubic phase morphology. Furthermore, the catalytic potential of Ag-NWs for the degradation of methyl orange dye (MO) was determined. The selected dye was degraded successfully that confirmed the catalytic potential of Ag-NWs. The authors concluded that Ag-NWs can be synthesized using plant extract having excellent morphological features as well as impressive catalytic potential.