Synthesis of metal nanoparticles using plant extracts is one of the most simple, convenient, economical, and environmentally friendly methods that mitigate the involvement of toxic chemicals. Hence, in recent years, several eco-friendly processes for the rapid synthesis of silver nanoparticles have been reported using aqueous extracts of plant parts such as the leaf, bark, roots, etc. This review summarizes and elaborates the new findings in this research domain of the green synthesis of silver nanoparticles (AgNPs) using different plant extracts and their potential applications as antimicrobial agents covering the literature since 2015. While highlighting the recently used different plants for the synthesis of highly efficient antimicrobial green AgNPs, we aim to provide a systematic in-depth discussion on the possible influence of the phytochemicals and their concentrations in the plants extracts, extraction solvent, and extraction temperature, as well as reaction temperature, pH, reaction time, and concentration of precursor on the size, shape and stability of the produced AgNPs. Exhaustive details of the plausible mechanism of the interaction of AgNPs with the cell wall of microbes, leading to cell death, and high antimicrobial activities have also been elaborated. The shape and size-dependent antimicrobial activities of the biogenic AgNPs and the enhanced antimicrobial activities by synergetic interaction of AgNPs with known commercial antibiotic drugs have also been comprehensively detailed.

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Green synthesis of silver nanoparticles using plant extracts and their antimicrobial activities: a review of recent literature

Our objective in this review article is to find out relevant information about methods of determination of antioxidant activity of silver nanoparticles. There are many studies dealing with mentioned problem and herein we summarize the knowledge about methods evaluating the antioxidant activity of silver nanoparticles reported so far. Many authors declare better antioxidant activity of silver nanoparticles compared to the extract used for synthesis of them. In this review, we focused on methods of antioxidant activity determination in detail to find out novel and perspective techniques to solve the general problems associated with the determination of antioxidant activity of silver nanoparticles.

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A Brief Overview on Antioxidant Activity Determination of Silver Nanoparticles.

Due to their versatile applications, gold (Au) and silver (Ag) nanoparticles (NPs) have been synthesized by many approaches, including green processes using plant extracts for reducing metal ions. In this work, we propose to use plant extract with active biomedical components for NPs synthesis, aiming to obtain NPs inheriting the biomedical functions of the plants. By using leaves extract of Clerodendrum inerme (C. inerme) as both a reducing agent and a capping agent, we have synthesized gold (CI-Au) and silver (CI-Ag) NPs covered with biomedically active functional groups from C. inerme. The synthesized NPs were evaluated for different biological activities such as antibacterial and antimycotic against different pathogenic microbes (B. subtilis, S. aureus, Klebsiella, and E. coli) and (A. niger, T. harzianum, and A. flavus), respectively, using agar well diffusion assays. The antimicrobial propensity of NPs further assessed by reactive oxygen species (ROS) glutathione (GSH) and FTIR analysis. Biofilm inhibition activity was also carried out using colorimetric assays. The antioxidant and cytotoxic potential of CI-Au and CI-Ag NPs was determined using DPPH free radical scavenging and MTT assay, respectively. The CI-Au and CI-Ag NPs were demonstrated to have much better antioxidant in terms of %DPPH scavenging (75.85% ± 0.67% and 78.87% ± 0.19%), respectively. They exhibited excellent antibacterial, antimycotic, biofilm inhibition and cytotoxic performance against pathogenic microbes and MCF-7 cells compared to commercial Au and Ag NPs functionalized with dodecanethiol and PVP, respectively. The biocompatibility test further corroborated that CI-Ag and CI-Au NPs are more biocompatible at the concentration level of 1–50 µM. Hence, this work opens a new environmentally-friendly path for synthesizing nanomaterials inherited with enhanced and/or additional biomedical functionalities inherited from their herbal sources.

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Green Synthesis of Gold and Silver Nanoparticles Using Leaf Extract of Clerodendrum inerme; Characterization, Antimicrobial, and Antioxidant Activities

Ultra Small, mono dispersed green synthesized silver nanoparticles using aqueous extract of Sida cordifolia plant and investigation of antibacterial activity.

This article reports the utilization of seed extract (GSE) from Gardenia jasminoides Ellis. in the synthesis of silver nanoparticles (Gs-AgNPs) with versatile biological activities. The synthesized Gs-AgNPs were spherical in shape, crystal lattice with an average size of 20 nm as confirmed by UV–vis spectrum, X-ray diffractometer (XRD), Transmission electron microscopy with Energy dispersive X-ray spectroscopy (TEM-EDS) and particle size analyses (PSA). Phenolic compounds, proteins, and terpenoids were likely involved in the Gs-AgNPs synthesis, as indicated by Fourier-transform infrared spectroscopy (FTIR) analysis. The minimum bactericidal concentration (MBC) of the Gs-AgNPs was 12.5 μg·ml−1 for S. enterica Typhimurium and 10 μg·ml−1 for S. aureus. The MBC of the Gs-AgNPs induced >70% bacterial cell death within 60 min, as confirmed by growth curve analysis followed by Confocal laser scanning microscope (CLSM). Gs-AgNPs showed the highest scavenging activity for 1, 2-diphenyl-1-picrylhydrazyl DPPH radical (92.3 ± 0.86%), Nitric oxide (NO) radical (72.5 ± 2.15%), and Hydrogen peroxide H2O2 radical (85.25 ± 1.45%). Anticancer results revealed an IC50 of 15.625 ± 1.3 μg·ml−1 for Gs-AgNPs, whereas it was 580.54 ± 2.5 μg·ml−1 for GSE. The Gs-AgNPs generated high reactive oxygen species (ROS) resulting in induced apoptosis as evident by up-regulation of apoptosis-related protein. In addition, the photocatalytic results revealed about 92% of the reduction in Coomassie Brilliant Blue dye color with Gs-AgNPs. Hence, this work provided economically viable and ecologically sustainable Gs-AgNPs as an alternative biomaterial for future therapeutic applications as antimicrobial, antioxidant, anti-cancer agents and in dye degradation for water remediation.

Sheng Wu

Papers

Characterization, antioxidant and antimicrobial activities of green synthesized silver nanoparticles from Psidium guajava L. leaf aqueous extracts.