Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus <Emphasis Type="Italic">Penicillium</Emphasis> sp.

In this work, the fungus Penicillium was used for rapid extra-/intracellular biosynthesis of gold nanoparticles. AuCl₄ ⁻ ions reacted with the cell filtrate of Penicillium sp. resulting in extracellular biosynthesis of gold nanoparticles within 1 min. Intracellular biosynthesis of gold nanoparticles was obtained by incubating AuCl₄ ⁻ solution with fungal biomass for 8 h. The gold nanoparticles were characterized by means of visual observation, UV–Vis absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The extracellular nanoparticles exhibited maximum absorbance at 545 nm in UV–Vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanocrystals. TEM exhibited the formed spherical gold nanoparticles in the size range from 30 to 50 nm with an average size of 45 nm. SEM and TEM revealed that the intracellular gold nanoparticles were well dispersed on the cell wall and within the cell, and they are mostly spherical in shape with an average diameter of 50 nm. The presence of gold was confirmed by EDX analysis.     

Synthesis of gelatin-capped gold nanoparticles with variable gelatin concentration

Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with controlled particle size were synthesized with simple variation of concentration of gelatin by reducing in situ tetrachloroauric acid with sodium citrate. The nanoparticles showed excellent colloidal stability. Transmission electron microscopy (TEM) revealed the formation of well-dispersed gold nanoparticles (AuNPs) with different sizes. The methodology produces particles 10–15 nm in size depending on the concentration of gelatin used. The measured AuNPs are 10, 11, 12, 13, 14, and 15 nm for AuNPs-gelatin 1, 0.5, 0.25, 0.1 and 0.05%, and pure AuNPs, respectively. The AuNPs-gelatin exhibit size-dependent localized surface plasmon resonance behavior as measured by UV–visible spectroscopy. UV–vis spectroscopy and TEM results suggest that higher concentration of gelatin favor smaller particle size and vice versa. FTIR spectroscopy analysis of AuNPs-gelatin revealed the amino bands and carboxyl peak of gelatin. The crystalline nature of AuNPs was investigated by X-ray diffraction.     

Biosynthesis of silver nanoparticles using <Emphasis Type="Italic">Ocimum sanctum</Emphasis> (Tulsi) leaf extract and screening its antimicrobial activity

Development of green nanotechnology is generating interest of researchers toward ecofriendly biosynthesis of nanoparticles. In this study, biosynthesis of stable silver nanoparticles was done using Tulsi (Ocimum sanctum) leaf extract. These biosynthesized nanoparticles were characterized with the help of UV–vis spectrophotometer, Atomic Absorption Spectroscopy (AAS), Dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Transmission electron microscopy (TEM). Stability of bioreduced silver nanoparticles was analyzed using UV–vis absorption spectra, and their antimicrobial activity was screened against both gram-negative and gram-positive microorganisms. It was observed that O. sanctum leaf extract can reduce silver ions into silver nanoparticles within 8 min of reaction time. Thus, this method can be used for rapid and ecofriendly biosynthesis of stable silver nanoparticles of size range 4–30 nm possessing antimicrobial activity suggesting their possible application in medical industry.     

Microwave-assisted rapid extracellular synthesis of stable bio-functionalized silver nanoparticles from guava (<Emphasis Type="Italic">Psidium guajava</Emphasis>) leaf extract

Our research interest centers on microwave-assisted rapid extracellular synthesis of bio-functionalized silver nanoparticles of 26 ± 5 nm from guava (Psidium guajava) leaf extract with control over dimension and composition. The reaction occurs very rapidly as the formation of spherical nanoparticles almost completed within 90 s. The probable pathway of the biosynthesis is suggested. Appearance, crystalline nature, size and shape of nanoparticles are understood by UV–vis (UV–vis spectroscopy), FTIR (fourier transform infrared spectroscopy), XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy) and TEM (transmission electron microscopy) techniques. Microwave-assisted route is selected for the synthesis of silver nanoparticles to carry out the reaction fast, suppress the enzymatic action and to keep the process environmentally clean and green.     

Synthesis and antibacterial activity of silver nanoparticles with different sizes

Silver nanoparticles with different sizes (7, 29, and 89 nm mean values) were synthesized using gallic acid in an aqueous chemical reduction method. The nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) absorption spectroscopy; the antibacterial activity was assessed using the standard microdilution method, determining the minimum inhibitory concentration (MIC) according to the National Committee for Clinical Laboratory Standards. From the microscopies studies (TEM) we observed that silver nanoparticles have spherical (7 and 29 nm) and pseudospherical shape (89 nm) with a narrow size distribution. The sizes of the silver nanoparticles were controlled by varying some experimental conditions. It was found that the antibacterial activity of the nanoparticles varies when their size diminishes.     

Fusarium solani: a novel biological agent for the extracellular synthesis of silver nanoparticles

We report extracellular biosynthesis of silver nanoparticles by Fusarium solani (USM-3799), a phytopathogen causing disease in onion, when challenged with 1 mM silver nitrate (AgNO₃). The formation of nanoparticles was characterized by visual observation followed by UV–Vis spectrophotometric analysis, which showed a peak at about 420 nm, which is very specific for silver nanoparticles. Further analysis carried out by Fourier Transform Infrared Spectroscopy (FTIR), provides evidence for the presence of proteins as capping agent, which helps in increasing the stability of the synthesized silver nanoparticles. Transmission Electron Microscopy (TEM) investigations confirmed that silver nanoparticles were formed. The synthesized silver nanoparticles were found to be polydispersed, spherical in the range of 5–35 nm with average diameter of 16.23 nm. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.     

Control of the aggregation behavior of silver nanoparticles in polyurethane matrix

By using N,N-dimethylformamide (DMF) as a solvent and reducing agent, and polyurethane (PU) as a structure-directing agent, flexible silver nanochains are formed under mild conditions with mean diameter of 15.97 and 35.6 nm, respectively. Some linear chain-like aggregates of silver nanoparticles with mean diameter of 6.69 nm are also formed by controlling the experimental condition. In parallel experiment, silver nanospheres with mean diameters of 5.76 nm, instead of nanochains are generated when antioxidants are added. After 3 days of aging, some nano clusters are transformed into triangular or hexagonal nanoplates. This aggregation behavior was characterized by UV–Vis spectroscopy, TEM, and powder X-ray diffraction. The aggregation mechanism of silver nanoparticles in the PU and ATPU was discussed. Our results provide potential application for new generation of nanodevice.     

Synthesis and Characterization of Ag@TiO2 Core-shell Nanoparticles and TiO2 Nanobubbles

Ag@TiO₂ core-shell structured particles of nano-size dimensions have been successfully prepared via a one-step way, which has proved quite effective in procuring stable colloids. Transmission electron microscopy (TEM) was employed to characterize the core size and the shell thickness, which typically were 20~40 nm and ~2 nm, respectively. X-ray diffraction (XRD) indicated the existence of silver. Optical absorption dependence on core size and synthetic temperature has been explored by UV–Vis absorption spectroscopy. Finally, the interesting titanium dioxide nanobubbles with silver core leached out by a unique means, were studied, which consequently proved the core-shell structure of the prepared nanoparticles, confirming the TEM observation.     

Mycogenic synthesis of silver nanoparticles by the Japanese environmental isolate <Emphasis Type="Italic">Aspergillus tamarii</Emphasis>

In this study, an environmental friendly process for the synthesis of silver nanoparticles (AgNPs) using a fungus Aspergillus tamarii has been investigated. The process of silver ion reduction by the fungal extracellular filtrate was spontaneous which lead to the development of an easy process for synthesis of silver nanoparticles. The AgNPs formed were characterized using UV–Visible spectrum, FTIR, and SEM. The results revealed that silver ions reduction by the fungal extracellular filtrate started at 420 nm after 0.5 h of incubation time. The FTIR peaks were observed at 1393, 1820, 2727, and 3545 cm⁻¹. The SEM result showed the distribution of spherical AgNPs ranging from 25 to 50 nm.     

Silver nanoparticles with gelatin nanoshells: photochemical facile green synthesis and their antimicrobial activity

In the current study, a facile green synthesis of silver-gelatin core–shell nanostructures (spherical, spherical/cubic hybrid, and cubic, DLS diameter: 4.1–6.9 nm) is reported via the wet chemical synthesis procedure. Sunlight-UV as an available reducing agent cause mild reduction of silver ions into the silver nanoparticles (Ag-NPs). Gelatin protein, as an effective capping/shaping agent, was used in the reaction to self-assemble silver nanostructures. The formation of silver nanostructures and their self-assembly pattern was confirmed by SEM, AFM, and TEM techniques. Further investigations were carried out using zeta-potential, UV–Vis, FTIR, GPC, and TGA/DTG/DTA data. The prepared Ag-NPs showed proper and acceptable antimicrobial activity against three classes of microorganisms (Escherichia coli Gram-negative bacteria, Staphylococcus aureus Gram-positive bacteria, and Candida albicans fungus). The antibacterial and antifungal Ag-NPs exhibit good stability in solution and can be considered as promising candidates for a wide range of biomedical applications.     

Methoxycarbonyl-terminated hyperbranched poly(amine-ester) as templates for synthesis of silver nanoparticles

Highly stable and spherical silver nanoparticles, stabilized by methoxycarbonyl-terminated hyperbranched poly(amine-ester) (HPAE-COOCH₃), were synthesized in water with reducing AgNO₃/HPAE-COOCH₃ using two methods, viz. NaBH₄ and ultraviolet irradiation. HPAE-COOCH₃ was found to play a key role in the formation of nanoparticles. UV–visible absorption, Transmission electron microscopic (TEM), and Fourier transform infrared spectroscopy (FT-IR) had been used to study the structure and characterization of the silver nanoparticles. The absorption peaks of the silver nanoparticles appear at ~420 nm in UV–visible absorption spectra; average particle size reduced by NaBH₄ is ~30 nm, which is ~10 and ~15 nm, respectively, when ultraviolet irradiation time is 12 and 24 h. FT-IR spectra confirm that there is strong interaction between silver nanoparticles and HPAE-COOCH₃. And silver nanoparticles/HPAE-COOCH₃ aqueous solution can keep stable for more than 3 months.     

Optical properties of pyridine funtionalized TbF<Subscript>3</Subscript> nanoparticles

The preparation of pyridine functionalized TbF₃ nanoparticles are described in this report. Synthesized nanoparticles were characterized using the TEM, UV/Vis, FTIR and photoluminescence spectroscopy. TEM micrograph reveals the nanorod shaped, uniform in size with a particles size in the range of 20–30 nm. FTIR spectrum shown characteristic absorption bands of pyridine and a small intensity band at 411 cm⁻¹ corresponding metal nitrogen ν(Tb–N) bonding. Uv-vis spectrum shown the characteristic absorption transitions of Tb³⁺ ion. A strong emission transition at 540 nm (⁵D₄ → ⁷F₅) was observed on excite by visible light at 414 nm.     

Synthesis,characterization and role of zero-valent iron nanoparticle in removal of hexavalent chromium from chromium-spiked soil

Chromium is an important industrial metal used in various products/processes. Remediation of Cr contaminated sites present both technological and economic challenges, as conventional methods are often too expensive and difficult to operate. In the present investigation, Zero-valent iron (Fe⁰) nanoparticles were synthesized, characterized, and were tested for removal of Cr(VI) from the soil spiked with Cr(VI). Fe⁰ nanoparticles were synthesized by the reduction of ferric chloride with sodium borohydride and were characterized by UV–Vis (Ultra violet–Visible) and FTIR (Fourier transform infrared) spectroscopy. The UV–Vis spectrum of Fe⁰ nanoparticles suspended in 0.8% Carboxymethyl cellulose showed its absorption maxima at 235 nm. The presence of one band at 3,421 cm⁻¹ ascribed to OH stretching vibration and the second at 1,641 cm⁻¹ to OH bending vibration of surface-adsorbed water indicates the formation of ferrioxyhydroxide (FeOOH) layer on Fe⁰ nanoparticles. The mean crystalline dimension of Fe⁰ nanoparticles calculated by XRD (X-ray diffraction) using Scherer equation was 15.9 nm. Average size of Fe⁰ nanoparticles calculated from TEM (Transmission electron microscopy) images was found around 26 nm. Dynamic Light Scattering (DLS) also showed approximately the same size. Batch experiments were performed using various concentration of Fe⁰ nanoparticles for reduction of soil spiked with 100 mg kg⁻¹ Cr(VI). The reduction potential of Fe⁰ nanoparticles at a concentration of 0.27 g L⁻¹ was found to be 100% in 3 h. Reaction kinetics revealed a pseudo-first order kinetics. Factors like pH, contact time, stabilizer, and humic acid facilitates the reduction of Cr(VI).     

Highly bacterial resistant silver nanoparticles: synthesis and antibacterial activities

In this article, we describe a simple one-pot rapid synthesis route to produce uniform silver nanoparticles by thermal reduction of AgNO₃ using oleylamine as reducing and capping agent. To enhance the dispersal ability of as-synthesized hydrophobic silver nanoparticles in water, while maintaining their unique properties, a facile phase transfer mechanism has been developed using biocompatible block co-polymer pluronic F-127. Formation of silver nanoparticles is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy. Hydrodynamic size and its distribution are obtained from dynamic light scattering (DLS). Hydrodynamic size and size distribution of as-synthesized and phase transferred silver nanoparticles are 8.2 ± 1.5 nm (σ = 18.3%) and 31.1 ± 4.5 nm (σ = 14.5%), respectively. Antimicrobial activities of hydrophilic silver nanoparticles is tested against two Gram positive (Bacillus megaterium and Staphylococcus aureus), and three Gram negative (Escherichia coli, Proteus vulgaris and Shigella sonnei) bacteria. Minimum inhibitory concentration (MIC) values obtained in the present study for the tested microorganisms are found much better than those reported for commercially available antibacterial agents.     

A hybrid electrochemical–thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical–thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm². The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 °C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV–Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22–75 nm based on Debye–Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30–40 nm. The blue shift was noticed in UV–Vis absorption spectra, the band gaps were found to be 5.40–5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.     

Analytical characterization of gold nanoparticle primary particles,aggregates, agglomerates,and agglomerated aggregates

Gold nanoparticles have been studied for many biomedical applications. However, alterations in the gold nanoparticles’ environment frequently lead to the formation of aggregates and agglomerates, which have not been well characterized. These new structures could significantly change the biological impact of the nanoparticles, so the appropriate characterization of these structures prior to biological administration is vital for the correct interpretation of toxicology results. By varying the solvent or heating under pressure, four reproducible gold nanoparticles structures were created: 10 nm primary particles, aggregates of the primary particles that contain non-reversible bonds between the individual nanoparticles, agglomerates of primary particles that contain reversible interactions between the individual nanoparticles, and agglomerated aggregates that have reversible bonds linking individual aggregates. Ultraviolet–visible (UV–Vis) spectroscopy, thermal gravitational analysis, and neutron activation analysis were each found to accurately measure the concentration of the primary particles. The primary particles measured 10 nm by dynamic light scattering (DLS) and had a spherical morphology by transmission electron microscopy (TEM) while the aggregates measured 110 nm by DLS and had a distorted morphology by TEM. The agglomerate and aggregated agglomerate samples both measured >1,000 nm by DLS, but the individual particles had significantly different morphologies by TEM. Multiple other analytical techniques, including ultracentrifugation, gel electrophoresis, and X-ray diffraction, also showed unique traits for each structure. The structural differences did not change in the presence of cell culture media or rat serum. In addition, the primary particles, aggregates, and agglomerates each had a unique UV–Vis spectrum, allowing for an inexpensive, rapid method to differentiate between the structures.     

Enhanced activity of chaperonin GroEL in the presence of platinum nanoparticles

The chaperonin protein GroEL was mixed with varying concentrations of K₂PtCl₄ followed by a 20-fold concentration of sodium borohydride to afford GroEL–platinum nanoparticle complexes in a ratio of between 1:25 and 1:2,000. Typical colour change, from colourless or pale yellow to brown, occurred that was dependent on the amount of platinum present. These complexes were characterised by UV/Vis, inductively coupled plasma optical emission spectroscopy, Fourier transform infra red, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy. TEM analysis revealed that the size of nanoparticles increased as the molar ratio of platinum to GroEL increased with an average size diameter of 1.72–3.5 nm generated with GroEL–platinum molar ratios of 1:125–1:2,000. Fourier-transform infrared spectroscopy (FTIR) spectra showed no distinct changes in the structure of GroEL but confirmed that the nanoparticles were attached to the protein. The effect of platinum nanoparticles on the ATPase activity of GroEL showed an activity of 5.60 μmol min⁻¹ ml⁻¹ (87 % increase over a control) at the molar ratio of GroEL–platinum nanoparticles of 1:25.     

One-pot synthesis of gold nanoparticles using tetradentate porphyrins

In this study, the meso-tetra (p-hydroxyphenyl) porphyrin and meso-tetra (m-hydroxyphenyl) porphyrin were coated on to gold nanoparticles (AuNPs) via thioacetate anchors which easily dissociate to form S–Au bonds. 4-tert-butyl phenyl thioacetate-AuNPs were prepared and used as a monodentate passivant to control the size of the tetradentate porphyrin-AuNPs. The porphyrin-coated AuNPs were characterized by UV–Vis, TEM, XRD, and XPS analyses. The tetradentate porphyrin-AuNPs size is within a range of 5–15 nm in diameter with exotic shapes. The plausible network formation for AuNP@p-TPP-SAc and the capping structure of the AuNP@m-TPP-SAc have been suggested.     

Entrapment of dye molecules within submicron silver particles

We describe a method for the preparation of metal–organic composites submicron particles. Specifically, the preparation of silver particle-clusters 150–200 nm in size, doped with an organic dye Congo-red, is reported. The use of sodium citrate coupled with sodium hypophosphite facilitated the formation of these particle-clusters, which were fully characterized by TEM analysis, Zeta potential and size measurements, scanning electron microscopy, UV–Vis measurements, and thermogravimetric analysis. The latter reveals a catalytic action of the metal on the thermal oxidative decomposition of the entrapped dye. The use of these particles to obtain dense thin metallic films was demonstrated by the coating of ITO glass.     

Synthesis and characterization of Mg-doped ZnO hollow spheres

Mg-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Mg:Zn atomic ratio from 0 to 7%. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and magnesium acetate tetrahydrate were heated under refluxing at 65 °C using methanol as a solvent. X-ray diffraction analysis reveals that the Mg-doped ZnO crystallizes in a wurtzite structure with crystal size of 5–12 nm. These nanocrystals self-aggregated themselves into hollow spheres of size of 800–1100 nm. High resolution transmission electron microscopy images show that each sphere is made up of numerous nanoparticles of average diameter 5–11 nm. The XRD patterns, SEM and TEM micrographs of doping of Mg in ZnO confirmed the formation of hollow spheres indicating that the Mg²⁺ is successfully substituted into the ZnO host structure of the Zn²⁺ site. Furthermore, the UV–Vis spectra and photoluminescence (PL) spectra of the ZnO nanoparticles were also investigated. The band gap of the nanoparticles can be tuned in the range of 3.36–3.55 eV by the use of the dopants.