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Graphical abstract In situ microwave-assisted synthesis of Ag NPs using PNIPAM microgel. Highlights • In situ microwave-assisted synthesis of Ag NPs using microgel as a template. • The prepared composite Ag NPs exhibited temperature responsive behaviour. • These particles were found to be monodispersed and highly crystalline, with average particle size of 10 nm. Abstract In this study, a simple environmentally greener "in situ " chemical synthesis has been developed to prepare silver nanoparticles (Ag NPs) from chemically reduced AgNO 3 in an aqueous media of thermo-responsive microgel, using glucose as a reducing agent and by adopting a microwave irradiation technique. The thermo-responsive microgel poly- N- isopropylacrylamide-co-2-hydroxyethyl acrylate, poly (NIPAM-co-HEA) 200 nm in size was prepared by surfactant free emulsion polymerisation of a selected mixture of N- isopropylacrylamide, methylene-bis-acrylamide and 2-hydroxyethyl acrylate. This microgel acts as a mere support to immobilize Ag NPs. The formation of Ag NPs and the thermo-responsive properties of the mixture were studied using UV–visible Spectroscopy. Their structures were characterised by FE-SEM and TEM. The Ag NPs prepared by this approach appear to be monodispersed with sizes which are <15 nm. Excellent biocompatibility, cell viability and environmentally responsive properties suggested that as-prepared composite particles are ideal candidate for antibacterial, biosensors and drug delivery applications. [ABSTRACT FROM AUTHOR]

We have demonstrated a one pot green protocol for the synthesis of highly monodispersed silver nanoparticles using leaves of Salvadora persica plant. When the leaf extract of Salvadora persica plant reacted with silver nitrate (AgNO 3 ) solution it resulted in the synthesis of highly monodispersed silver nanoparticles with an average size of 3 nm. These nanoparticles were then completely characterized by UV–Visible spectroscopy, Transmission Electron Microscopy, Energy Dispersive Analysis of X-Rays, X-ray diffraction analysis and Fourier Transform Infrared analysis. [ABSTRACT FROM AUTHOR]

A unique way to control the size and antibacterial activities of silver nanoparticles (Ag NPs) using three different leaf conditions (fresh, oven-dried and sun-dried) of Alstonia scholaris has been reported in this paper. The extract of the A. scholaris leaf acts both as a reducing and stabilizing agent in the formation of Ag nanoparticles. The characteristic surface plasmon peak (415 nm), X-ray diffraction (XRD) studies and energy dispersive spectroscopy (EDS) confirmed the formation of crystalline green Ag nanoparticles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that there was a difference in size for the Ag NPs synthesized from different leaf conditions. Antibacterial studies with both Gram-positive and Gram-negative bacteria showed that Ag NPs synthesized from the fresh leaves displayed the best antibacterial activity, which can be attributed to the size effect of the nanoparticles. [ABSTRACT FROM AUTHOR]

This paper presents a facile, and ecofriendly method to prepare colloidal silver nanoparticles (AgNPs) at room temperature using bulk silver bars, bi-distilled water, trisodium citrate, and a direct-current voltage source. AgNP formation was confirmed and characterized by ultraviolet–visible spectroscopy, transmission electron microscopy and X-ray diffraction. Their antibacterial activity was examined by disc diffusion and minimum inhibitory concentration (MIC) techniques against three bacterial strains, including the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa . Results showed that the size of AgNPs formed was about 19.7±4.3 nm with nearly spherical shape and high purity. The antibacterial activity of as-prepared AgNPs was determined through zones of inhibition against the growth of three bacterial strains on agar. MIC analysis showed that S. aureus had resistance to AgNPs that was about 2–3 times higher than those of E. coli and P. aeruginosa , and that resistance ability depended on the bacterial concentrations inoculated. This work revealed the effective method of synthesizing a large quantity of colloidal AgNPs with high antibacterial effectiveness and potential application in different fields. [ABSTRACT FROM AUTHOR]

In this investigation, silver nanoparticles having a size ranging from 5 to 40 nm have been fast-biosynthesized by Tamarix gallica plant extract. The Ag nanoparticles obtained at room temperature by exposing the silver nitrate ions to the plant extract in an aqueous solution were characterized by UV–vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy techniques. The biosynthesis process of spherical Ag nanoparticles exhibits a high rate of bioreduction being less than a 5 min reaction. UV–vis spectroscopy shows a surface plasmon resonance band located at 426.7 nm. The FT-IR spectrum of nanoparticles showed the presence of CO functional group that can be associated with the removal of aromatic compounds (benzenes) to form the nanometer solids. The antibacterial activity against Escherichia coli of silver nanoparticles synthesized with Tamarix gallica extract was confirmed. [ABSTRACT FROM AUTHOR]

Silica core shell silver nanoparticles (Ag@SiO 2 NPs) have been prepared by a one step synthesis in an eco-friendly way. Biological fermented product, i.e. whisky was used as a reducing agent for silver ions and as a catalyst for the formation of silica shell on silver nanoparticles (AgNPs). The structural and morphological studies were done by various analytical techniques to reveal its crystalline nature and core-shell structure. The catalytic activity of Ag@SiO 2 NPs for the reduction of mixture of 4-nitrophenol (4-NP) and rhodamine-B (Rh-B) in presence of NaBH 4 and its reusability are demonstrated. The antibacterial activity of Ag@SiO 2 NPs against Escherichia coli ( E. coli ), Bacillus cereus ( B. cereus ), and Staphylococcus aureus ( S. aureus ) was studied. [ABSTRACT FROM AUTHOR]

The development of new type of antimicrobials without drug-resistence has increased exponentially. “One pot” green synthesis method was developed to synthesize the graphitic-phase C 3 N 4 (g-C 3 N 4 ) loaded with metal Ag nanoparticles (Ag NPs) using grape seed extract as reducing agent and stabilizing agent, which is rapid, economic and environmentally friendly. Ag NPs and g-C 3 N 4 sheets have strong interaction between Ag atoms and –C–N–, –C=N– bonds in g-C 3 N 4 sheets, resulting in successful deposition of AgNPs on g-C 3 N 4 sheets. The as-prepared g-C 3 N 4 /Ag nanocomposite shows better antibacterial activity than the green synthesized bare Ag NPs, showing great promise in application for new antibacterial material. [ABSTRACT FROM AUTHOR]

One step phytosynthesis of highly stabilized silver nanoparticles (AgNPs) had been produced by using the extract of Piper nigrum (black pepper) as a reducing and a capping agent in aqueous medium, without the addition of any other chemicals. UV–visible (UV–vis) spectra showed the formation of AgNPs by observing the surface plasmon resonance (SPR) band at 444 nm. X-ray diffraction (XRD) analysis confirmed the formation of AgNPs with face centered cubic (fcc) structure. Fourier transform infra-red (FT-IR) spectra were used to identify the functional groups present in the biomolecules for reduction and capping of AgNPs. The electrochemical behaviour was carried out by cyclic voltammetry (CV). Oval-like morphology of the sample was confirmed by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). Elemental composition was found out by the energy dispersive X-ray analysis (EDX). The antibacterial activities were carried out and revealed good results. This phytosynthetic approach is facile, inexpensive, reproducible, and eco-friendly. [ABSTRACT FROM AUTHOR]

In this investigation, we report the formation of new 3-D aggregates consisting of Ag-Au nanoparticles obtained in aqueous solution by a facile method using Aloysia triphylla plant extract as a reducing and stabilizing agent. SEM and EDS analysis reveal that the dimensions of 3-D arrays are estimated to be about 2.5 µm wide, 0.5 µm thick, and 2 µm long. The 3-D geometric aggregates have strong microstructures that are similar to those of ordinary crystalline materials. The microstructures are close-packed with straight edges and facets but do not have grain boundaries. HRTEM images indicate that the 3-D arrays are a consequence of the nanoparticles aggregation inside an organic matrix and the presence of Au forming the BNPs. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we report a simple and environment friendly method for synthesis of well dispersed and stable silver nanoparticles using semen cassiae extract as both reducing and stabilizing agents in aqueous solution without employing any other reducing and capping agents. The formation of silver nanoparticles was observed by change of color from light yellow to red and the UV–vis absorption spectroscopy. The effect of reaction time and semen cassiae amounts on the synthesis of silver nanoparticles was studied. The morphology of the as prepared silver nanoparticles was examined by using HRTEM, which showed that the silver nanoparticles were spherical in shape with a size distribution from 2nm to 30nm. The crystalline structure of the silver nanoparticles was confirmed by XRD analysis. The as synthesized silver nanoparticles were tested against Escherichia coli and the obtained data were indicative of good antibacterial properties of the materials. The method presented in this paper provides a very promising approach to synthesize other noble nanoparticles using renewable materials as reducing and capping agents. [Copyright &y& Elsevier]

Abstract: Biosynthesis of silver nanoparticles (AgNPs) using Acinetobacter calcoaceticus PUCM 1005 and their application in biofilm disruption is described. Extracellular AgNPs were produced by 48h grown culture when challenged with silver nitrate. AgNPs synthesis was found to be optimum at 40mM AgNO3, 40°C temperature and pH 5. UV–vis spectroscopy, energy dispersive spectra and X-ray diffraction analysis confirmed presence of AgNPs. Electron microscopy revealed the size range to be 4–40nm. These AgNPs exhibited higher activity against planktonic Gram negative pathogens. However, they could disrupt biofilm formed by Gram negative and Gram positive pathogenic microorganisms. AgNP synthesis was protein mediated. [Copyright &y& Elsevier]

Abstract: A completely green and large scale controlled synthesis of stable, smaller sized (<5nm) and monodispersed quasi spherical starch-capped silver nanoparticles (Ag NPs) using maltose as the reducing agent without any complexant or accelerator is presented. High concentration of the reducing saccharides produced via hydrolysis of maltose and partial hydrolysis of starch as the reaction time increases controls the particle diameter within the smaller size range. [Copyright &y& Elsevier]

Abstract: Bovine bone is employed as a template to support silver particles using the simple impregnation-reduction method of synthesis. SEM studies show that micro, submicro and nano silver crystals grow up on the surface and around bone pores with high faceted structures (hexagons and squares). More complex silver structures are also generated from the stacking of irregular silver plates. UV–vis spectra of silver nanoparticles in the silver-bone composites show the surface plasmon resonance band of Ag nanoparticles at 411nm. TEM studies show Ag-nanoparticles below 50nm with a FCC structure as confirmed by SAED. [Copyright &y& Elsevier]

Abstract: In the present work, we first report a low-cost, eco-friendly and simple procedure for biosynthesis of silver nanoparticles (Ag NPs) using plant fungus Puccinia graminis as reducing and capping agent. UV–vis spectroscopy, XRD, FTIR, FESEM and NC-AFM analyses were performed to confirm the formation of nanoparticles. Biologically synthesized Ag NPs showed UV peak at 427nm with surface plasmon resonance found similar to silver. The FTIR spectra of Ag NPs exhibited prominent peaks at 3353, 2917, 2851, 1450.86, 1414.48, 946.20, 615.77 and 466.89cm−1. XRD patterns confirmed the formation of Ag NPs with face centered cubic structures. NC-AFM and FESEM images showed the formation of spherical, well dispersed Ag NPs in the size range of 30–120nm, respectively. [Copyright &y& Elsevier]

Abstract: A hybrid organo-inorganic hybrid composite material based on conducting polymer, poly(o-toluidine) (POT)–silver (Ag) nanoparticles has been successfully synthesized by performing chemical oxidative polymerization of o-toluidine in the presence of negatively charged Ag nanocolloids. A plausible mechanism for the formation of POT–Ag composite is presented. The POT–Ag nanocomposite was characterized for morphological, structural, thermal and electrical properties. Transmission electron microscopy image of POT–Ag shows that Ag nanoparticles of ∼20 nm of sizes are well dispersed in the POT matrix. XRD and TGA results show that the composite is more crystalline and more thermally stable. UV–Vis absorption spectrum of the composite showed surface plasmon resonance absorption band at around 410 nm indicating that Ag nanoparticles are existed in the polymer matrix. Strikingly, the POT–Ag composite exhibits higher electrical conductivity (1.28 S/cm) than that of POT (1.09×10−3 S/cm). This method is simple and it could provide an opportunity to design novel conducting polymer–metal nanocomposites. [Copyright &y& Elsevier]

Abstract: Stable aqueous dispersions of silver nanoparticles have been synthesized from an organometallic precursor dissolved in an organic phase. Hydrogen gas is used to reduce the precursor to form silver nanoparticles which spontaneously transfer into an immiscible aqueous phase where they are stabilized. This route provides a simple pathway for the preparation of aqueous nanoparticle solutions and avoids production of the inorganic ions that are usually associated with aqueous methods. The effectiveness of a variety of aqueous stabilizing agents is evaluated. All products show plasmon absorption bands characteristic of silver nanoparticles and transmission electron microscopy reveals most particles to be below 40 nm in diameter. [Copyright &y& Elsevier]

Abstract: Silica–silver heterogeneous nanocomposite particles were successfully prepared by facile route including alcohol reduction method. Thiol groups were employed as a chemical protocol to make a binding between silver nanoparticle and silica surface. After the reaction for 10 min, a large number of quasi-spherical silver nanoparticles with an average size of 6.9 nm in diameter were homogeneously formed on the surface of silica particles. The immobilized silver nanoparticles grew to large ones with an average size of 10.6 nm in diameter after additional reaction for 2 h. The resulting nanocomposite particles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), UV–vis spectrophotometer, and X-ray diffraction (XRD) analysis. [Copyright &y& Elsevier]

Abstract: The fungus, Aspergillus flavus when challenged with silver nitrate solution accumulated silver nanoparticles on the surface of its cell wall in 72 h. These nanoparticles dislodged by ultrasonication showed an absorption peak at 420 nm in UV–visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 8.92±1.61 nm) by the fungus. X-ray diffraction spectrum of the nanoparticles confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the silver nanoparticles. These protein-stabilized silver nanoparticles produced a characteristic emission peak at 553 nm when excited at 420 nm in photoluminescence spectrum. The use of fungus for silver nanoparticles synthesis offers the benefits of eco-friendliness and amenability for large-scale production. [Copyright &y& Elsevier]

Abstract: We have prepared colloidal silver nanoparticles by reducing a high molar concentration of AgNO3 (up to 0.735 M) with glycerol in the presence of m-phenylenediamine. These silver nanoparticles had anisotropic shapes, including truncated rectangles, truncated triangles, and spheroid-type particles. The UV–Vis spectra of these nanoparticle systems display two distinct plasmon modes and a shoulder that correspond to the in-plane dipole, in-plane quadruple, and out-of-plane dipole resonances, respectively. The size and coating thickness of the nanoparticles are controllable while retaining their size distribution. We have used scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and, UV–Vis spectroscopy to characterize the silver products obtained. [Copyright &y& Elsevier]

Abstract: The biosynthesis of nanoparticles has been proposed as a cost effective environmental friendly alternative to chemical and physical methods. Microbial synthesis of nanoparticles is a green chemistry approach that interconnects nanotechnology and microbial biotechnology. In this present study, synthesis of silver nanoparticles (AgNPs) has been demonstrated using a metabolically versatile actinobacteria Rhodococcus sp. by reducing aqueous silver nitrate. The AgNPs were characterized by Ultraviolet–Visible (UV–vis) Spectrometer, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDAX), Dynamic Light Scattering (DLS), Selected Area Diffraction Pattern (SAED) and Transmission Electron Microscopy (TEM). The TEM showed spherical particles with an average size of 10nm. The SAED pattern showed the characteristic Bragg peaks of (111), (200), (220) and (311) facets of the face centered cubic (fcc) silver nanoparticles and confirmed that these nanoparticles are crystalline in nature. The synthesis of AgNPs is a biosynthesis process where cell enzyme systems of Rhodococcus sp. may take part in synthesis process. [Copyright &y& Elsevier]

Abstract: Silver nanoparticles have been successfully synthesized by the sonochemical route using sodium borohydride and sodium citrate as the reducing agents. The effect of the reducing agents on the particle size and morphology has been studied by carrying out the two reactions at the same ultrasound frequency (20KHz). The strong reducing agent (NaBH4) produced spherical silver nanoparticles of sizes 10nm whereas sodium citrate led to much smaller silver nanoparticles of ~3nm diameter. Powder X-ray diffraction studies reveal a high degree of crystallinity and monophasic silver particles. UV–Visible studies show the presence of a surface plasmon band at 405nm. However the reflectance spectra give a broad band between 340 and 360nm which is characteristic for the quasi-spherical silver nanoparticles. The specific surface area was found to be 2.6 and 13.1m2/g and the pore radius was found to be 15.2 and 12.3Å for silver nanoparticles obtained by the sodium borohydride and sodium citrate reduction respectively. [ABSTRACT FROM AUTHOR]

Abstract: This article presents a study about the synthesis of colloidal silver (Ag)/biopolymer where Ag submicron particles were prepared in situ on bacterial cellulose (BC) produced by Gluconacetobacter xylinus. Different reducing agents were compared (hydrazine, hydroxylamine or ascorbic acid) together with the influence of gelatin or polyvinylpyrrolidone (PVP) employed as colloid protectors. Particle size distribution and morphology were investigated by scanning electron microscope (SEM). SEM images show silver nanoparticles (40–100 nm) size range attached on (BC) microfibrils. XRD analyses confirmed the Ag cubic phase deposited on to BC fibrils. The ash contents determined by thermogravimetric analyses have indicated high level of silver loading on the obtained composites. [Copyright &y& Elsevier]

Abstract: The microwave-based thermal process was applied to the preparation of dendrimer-protected silver nanoparticles. The formation of silver nanoparticles occurs rapidly in a single step, carried out by directly heating a third-generation poly(propyleneimine) dendrimer–AgNO3 aqueous solution in a microwave oven without the introduction of additional reducing reagents and protective reagents. The nanoparticles thus formed were characterized by UV–vis spectra and transmission electron microscopy (TEM). The influence of the molar ratio of dendrimer to silver on the formation of silver particles was also examined. [Copyright &y& Elsevier]

• Co-precipitation method was used to synthesize CuO-NiO-ZnO trimetallic oxide NP. • Reductions in number of bacterial colonies show NPs are good antibacterial agents. • FESEM shows rupture of bacterial cell wall and leakage of intracellular components. Bacterial resistance to antibiotics has been a global concern. Metal oxide nanoparticles have emerged as effective antimicrobial agents. In this work, co-precipitation method was used to synthesize CuO-NiO-ZnO mixed metal oxide (MMO) nanoparticles. Nanoparticles were characterized using X-ray powder Diffraction (XRD) analysis which confirmed the formation of all three phases, Field Emission Scanning Electron Microscope (FESEM) analysis, Fourier Transform-Infrared Spectroscopy (FTIR), UV–Visible Absorption Spectroscopy and Transmission electron microscopy (TEM) analysis showed the particle size distribution of nanoparticle. Bacterial growth curve, reduction in bacterial CFU (colony forming unit) and cell integrity study confirmed the antibacterial activity of MMO nanoparticle and showed detrimental effect against Escherichia coli and Staphylococcus aureus bacterial strains. Nanoparticle attachment to the bacterial cell wall and ultimate annihilation of the cell was observed in the FESEM study of interaction of bacterial cell. [ABSTRACT FROM AUTHOR]

• A novel green synthesis method is employed for the synthesis of copper nanoparticles. • The average size of the synthesized Cu nanoparticles is in the range of 5–25 nm. • The obtained nanoparticles have shown good antibacterial activity against gram-positive and gram-negative bacteria. In the present report, for the first time aqueous extract of Curcuma longa powder is used for the synthesis of Copper nanoparticles (Cu NPs) using a simple and cost effective method. Morphology, size, crystallinity, composition and microstructure of the synthesized Cu Nps are studied. Size of the particles are in the range of 5–20 nm. In addition to the above, antibacterial activity of the obtained Cu NPs is tested for both gram-positive and gram-negative microorganisms. Zone of inhibition of Cu NPs for gram positive bacteria is more compared to gram negative bacteria. The current work on green synthesis of metallic nanoparticles can be considered as an alternative method to avoid the usage of hazardous compounds and bitter reaction conditions in the production of metal nanoparticles. The obtained Cu NPs with their distinctive structural properties and effective biological effects can be used in applications viz. antimicrobial, antifungal, anticancer activity. [ABSTRACT FROM AUTHOR]