Converting ultrafine silver nanoclusters to monodisperse silver sulfide nanoparticles via a reversible phase transfer protocol

To achieve better control of the formation of silver sulfide (Ag₂S) nanoparticles, ultrasmall Ag nanoclusters protected by thiolate ligands (Ag₄₄(SR)₃₀ and Ag₁₆(GSH)₉) are used as precursors, which, via delicate chemistry, can be readily converted to monodisperse Ag₂S nanoparticles with controllable sizes (4–16 nm) and switchable solvent affinity (between aqueous and organic solvents). This new synthetic protocol makes use of the atomic monodispersity and rich surface chemistry of Ag nanoclusters and a novel two-phase protocol design, which results in a well-controlled reaction environment for the formation of Ag₂S nanoparticles.

Open image in new window

     

Comprehensive study on surfactant role on silver nanoparticles (NPs) prepared via modified Tollens process

Surfactants represent not only commonly used wetting agents but also substances that can be used as growth modifiers in the process of solid nanoparticle (NP) preparation. In this study we report influential character of different types of surfactants – i.e. ionic (SDS, CTAC) and non-ionic (Tween 80) – on fundamental characteristics of silver NPs, which were prepared by a modified Tollens process. The influential character of surfactants was evaluated throughout a reasonable improvement of the polydispersity (in the case of the tested non-ionic surfactants from 8.5% even down to 2.5%) and in the case of ionic surfactant, SDS and CTAC, also significant change of zeta potential (from −20 to −50 mV for the highest tested concentration of SDS). A slight influence of the tested surfactants was observed on the sizes of the prepared silver NPs. Therefore the obtained results from the performed surfactant-assisted syntheses revealed a possibility how to tailor silver NPs by means of their polydispersity and zeta potential according to the application demands.     

Preparation of high surface area silver powder via Tollens process under sonication

High surface area silver powder was prepared through Tollens process. The process involves reduction of Tollens reagent under sonication at room temperature. By gradually adding Tollens reagent into the mixture of glucose solution and sodium hydroxide solution, the silver powder forms immediately without silver mirror formation at container wall. The powders prepared through this process were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size distribution and surface area. The powders were cubic crystalline silver with bimodal distribution and primary particle size of < 1 μm and surface area of 1.8 m²/g. The yield of silver powder was higher than 99%.     

Temperature and amino acid-assisted size- and morphology-controlled photochemical synthesis of silver decahedral nanoparticles

Stable silver decahedron nanoparticles were produced under the blue light irradiation (light-emitting diodes) of a modified precursor solution that has been previously reported. To improve the formation of the nano-decahedrons under blue light, we proposed the use of amino acids with electrically charged side chains (L-arginine, L-lysine and L-histidine). Our results show that L-arginine and L-lysine are best suited to improve the yield of the decahedrons. We also followed the kinetics of the photochemical synthesis under different irradiance conditions of 80, 50 and 15?mW/cm². The maximum irradiance, 80?mW/cm², resulted in a synthesis that was twice as fast as those associated with lower irradiances, and the corresponding decahedron yield was higher. The optimal temperature of the precursor solution for the improvement of the photochemical synthesis of silver decahedrons with Triton X-100 as a surfactant was also determined.     

Highly efficient in vitro biosynthesis of silver nanoparticles using Lysinibacillus sphaericus MR-1 and their characterization

Abstract

Silver nanoparticles (AgNPs) have been widely used in diverse fields due to their superior properties. Currently the biosynthesis of AgNPs is in the limelight of modern nanotechnology because of its green properties. However, relatively low yield and inefficiency diminish the prospect of applying these biosynthesized AgNPs. In this work, a rapid mass AgNP biosynthesis method using the cell-free extract of a novel bacterial strain, Lysinibacillus sphaericus MR-1, which has been isolated from a chemical fertilizer plant, is reported. In addition, the optimum synthesis conditions of AgNPs were investigated. The optimum pH, temperature, dosage, and reaction time were 12, 70 °C, 20 mM AgNO₃, and 75 min, respectively. Finally, AgNPs were characterized by optical absorption spectroscopy, zeta potential and size distribution analysis, x-ray diffraction, electron microscopy, and energy-dispersive x-ray spectroscopy. The results revealed that these biosynthesized AgNPs were bimolecular covered, stable, well-dispersed face centered cubic (fcc) spherical crystalline particles with diameters in the range 5–20 nm. The advantages of this approach are its simplicity, high efficiency, and eco-friendly and cost-effective features.     

Green synthesis of silver nanoparticles from purple acid phosphatase apoenzyme isolated from a new source Limonia acidissima

Green synthesis of nanoparticles is regarded as a safe and non-toxic process whereas conventional synthesis using chemical methods produces toxic substance. This study provides a novel insight for enzymatic synthesis method of silver nanoparticles using purple acid phosphatase, isolated from Limonia acidissima (wood apple) as a new source and used in the synthesis of silver nanoparticles. Stable silver nanoparticles were produced by sonochemical method using apoenzyme as a stabilising and capping agent and were characterised by various physicochemical techniques like UV–Visible spectroscopy, Fourier-transform infrared, X-ray diffraction and transmission electron microscopy. X-ray study shows that nanoparticles are composed of silver and silver oxide. The synthesised nanoparticles exhibited excellent antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus.     

Medicinal plants mediated the green synthesis of silver nanoparticles and their biomedical applications

The alarming effect of antibiotic resistance prompted the search for alternative medicine to resolve the microbial resistance conflict. Over the last two decades, scientists have become increasingly interested in metallic nanoparticles to discover their new dimensions. Green nano synthesis is a rapidly expanding field of interest in nanotechnology due to its feasibility, low toxicity, eco‐friendly nature, and long‐term viability. Some plants have long been used in medicine because they contain a variety of bioactive compounds. Silver has long been known for its antibacterial properties. Silver nanoparticles have taken a special place among other metal nanoparticles. Silver nanotechnology has a big impact on medical applications like bio‐coating, novel antimicrobial agents, and drug delivery systems. This review aims to provide a comprehensive understanding of the pharmaceutical qualities of medicinal plants, as well as a convenient guideline for plant‐based silver nanoparticles and their antimicrobial activity.     

Eco-friendly green synthesis of silver nanoparticles and their potential applications as antioxidant and anticancer agents

Abstract

Eco-friendly green synthesis of nanoparticles using medicinal plants gained immense importance due to its potential therapeutic uses. In the current study, silver nanoparticles (AgNPs) were synthesized using water extract of Jurinea dolomiaea leaf and root at room temperature. MTT assay was used to study anticancer potential of AgNPs against cervical cancer cell line (HeLa), breast cancer cell lines (MCF-7), and mouse embryonic fibroblast (NIH-3 T3) cell line for toxicity evaluation. The antioxidant potential was evaluated using stable DPPH radicals. In addition, the apoptotic nuclear changes prompted by AgNPs in more susceptible HeLa cells were observed using fluorescence microscope through DAPI and PI staining. Physiochemical properties of biosynthesized AgNPs were characterized using various techniques. AgNPs were formed in very short time and UV–vis spectra showed characteristic absorption peak of AgNPs. SEM and TEM showed spherical shape of AgNPs and XRD revealed their crystalline nature. EDX analysis revealed high percentage of silver in green synthesized AgNPs. FTIR analysis indicated involvement of secondary metabolites in fabrication of AgNPs. In vitro cytotoxic and antioxidant study revealed that herb and biosynthesized AgNPs exhibited significant dose-dependent and time-dependent anticancer and antioxidant potential. Furthermore, study on normal cell line and microscopic analysis of apoptosis revealed that AgNPs exhibited good safety profile as compared to cisplatin and induces significant apoptosis effect. Based on the current findings, it is strongly believe that use of J. dolomiaea offers large scale production of biocompatible AgNPs that can be used as alternative anticancer agents against cancer cell lines tested.     

Highly efficient in vitro biosynthesis of silver nanoparticles using Lysinibacillus sphaericus MR-1 and their characterization

Silver nanoparticles (AgNPs) have been widely used in diverse fields due to their superior properties. Currently the biosynthesis of AgNPs is in the limelight of modern nanotechnology because of its green properties. However, relatively low yield and inefficiency diminish the prospect of applying these biosynthesized AgNPs. In this work, a rapid mass AgNP biosynthesis method using the cell-free extract of a novel bacterial strain, Lysinibacillus sphaericus MR-1, which has been isolated from a chemical fertilizer plant, is reported. In addition, the optimum synthesis conditions of AgNPs were investigated. The optimum pH, temperature, dosage, and reaction time were 12, 70 °C, 20 mM AgNO₃, and 75 min, respectively. Finally, AgNPs were characterized by optical absorption spectroscopy, zeta potential and size distribution analysis, x-ray diffraction, electron microscopy, and energy-dispersive x-ray spectroscopy. The results revealed that these biosynthesized AgNPs were bimolecular covered, stable, well-dispersed face centered cubic (fcc) spherical crystalline particles with diameters in the range 5–20 nm. The advantages of this approach are its simplicity, high efficiency, and eco-friendly and cost-effective features.     

Bio-mechanochemical synthesis of silver nanoparticles with antibacterial activity

By using a bio-mechanochemical approach combining mechanochemistry (ball milling) and green synthesis for the first time, silver nanoparticles (Ag NPs) with antibacterial activity were successfully synthesized. Concretely, eggshell membrane (ESM) or Origanum vulgare L. plant (ORE) and silver nitrate were used as environmentally friendly reducing agent and Ag precursor, respectively. The whole synthesis took 30?min in the former and 45?min in the latter case. The photon cross-correlation measurements have shown finer character of the product in the case of milling with Origanum. UV–Vis measurements have shown the formation of spherical NPs in both samples. TEM study has revealed that both samples are composites of nanosized silver nanoparticles homogenously dispersed within the organic matrices. It has shown that the size and size distribution of the silver nanoparticles is smaller and more uniform in the case of eggshell membrane matrix implying lower silver mobility within this matrix. The antibacterial activity was higher for the silver nanoparticles synthesized with co-milling with Origanum plant than in the case of milling with eggshell membrane.     

Synthesis of size- and shape-controlled monodisperse PbSe quantum dots via a green approach

Spherical, octahedral, and cubic shaped PbSe quantum dots were successfully synthesized by virtue of a green chemical route, using environmentally friendly N,N-dimethyl-oleoyl amide as the solvent of Se. The process eliminates trioctylphoshine from the synthesis, using oleic acid as capping ligand in the noncoordinating solvent. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopic (EDS), were used to characterized the samples. The crystalline size can be tuned in a range from 8 nm to 16 nm by varing the reaction time or growth temperature. Based on the evidence of TEM images, the mechanism of PbSe quantum dots evolution from spherical to cubic structure has also been discussed. We found that the growth temperature played an important role in the morphology of PbSe quantum dots. This finding will enhance our understanding for the formation mechanism of nanomaterials with special shapes.     

Mass-spectrometric investigations of the synthesis of silver nanoparticles via electrolysis

The synthesis of silver nanoparticles during electrolysis of NaCl solutions and silver electrodes was controlled by using UV absorption and mass-spectrometric methods. For mass-spectrometric measurements, the laser desorption/ionization method and a time of flight (TOF) spectrometer were employed. Results of investigations show the possibility of formation of small silver nanoparticles (of the cluster size ?7) or their compounds.     

Biosynthesis of silver nanoparticles in collagen gel improves their medical use in periodontitis treatment

Silver nanoparticles (AgNP) suspensions were biosynthesized by silver ions reduction in the presence of collagen, a nontoxic, organic polymer, intending to improve their medical use in periodontitis treatment. Spectrophotometric measurements showed a time- and concentration-dependent increase of AgNP formation in each suspension variant. Transmission electron microscopy revealed spherical morphology of AgNP in collagen and their mean diameter size was around 30?nm. The particle size distribution and zeta potential values of AgNP in collagen were determined by dynamic light scattering measurements. The surface charge of AgNP in collagen was positive, while commercial AgNP stabilized in citrate had negative surface charge. In vitro cytotoxicity testing of AgNP in collagen showed that they were biocompatible with human gingival fibroblasts in a wider range of concentrations than commercial nanoparticles. The antibacterial activity of AgNP in collagen against two pathogenic strains present in the periodontal pocket was dose-dependent and higher than that of AgNP in citrate. All these results demonstrated that AgNP prepared in collagen gel had improved properties, like small diameter, positive surface charge, high biocompatibility in human gingival fibroblasts, efficiency against bacterial growth and, thus, better therapeutic potential in periodontal disease treatment.     

Effect of temperature in synthesis of silver nanoparticles in triblock copolymer micellar solution

Knowing that poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) in aqueous solution is thermoresponsive, the effect of temperature on formation and stabilisation of silver nanoparticles has been investigated systematically. Synthesis of silver nanoparticles was achieved from silver ammonia complex [Ag(NH₃)₂]⁺ in aqueous solution of hydroxyl terminated PEO–PPO–PEO at four different temperatures. A non-Arrhenius behaviour for the rate of silver reduction with temperature was observed. The hydrodynamic diameter of the composite coils suddenly increased at certain intermediate time indicating sudden agglomeration of individual micelles to form bigger network structures. The size and the distribution of the nanoparticles show a bimodal distribution at the lowest temperature. At intermediate temperature, particles of the smallest size with a narrow distribution was achieved. At the highest temperature, a bunch-like particle morphology was found. Chemical changes in polymer properties were observed at higher temperatures. The results suggest that at a lower temperature, a change in polymer morphology play an important role in controlling the particle size and their distribution, whereas at a higher temperature, this role is shifted to the chemical change of the polymer. At an intermediate temperature, a balance between the two effects provides the optimum condition for formation of silver nanoparticles of small size and narrow distribution.     

化学还原法制备纳米银粒子及其表征

采用化学还原法, 通过一系列条件实验,借助紫外-可见分光光度计(UV-vis)得到最佳实验条件,在最佳实验条件下制得紫黑色溶胶,在40℃下真空干燥3h,获纳米银粉.制备的纳米银粉用X射线衍射仪(XRD)和透射电镜(TEM)分析表明,其粒径大小分布范围窄,形状为单一球形,平均粒径为18nm.     

Shaped gold and silver nanoparticles

Advance in the synthesis of shaped nanoparticles made of gold and silver is reviewed in this article. This review starts with a new angle by analyzing the relationship between the geometrical symmetry of a nanoparticle shape and its internal crystalline structures. According to the relationship, the nanoparticles with well-defined shapes are classified into three categories: nanoparticles with single crystallinity, nanoparticles with angular twins, and nanoparticles with parallel twins. Discussion and analysis on the classical methods for the synthesis of shaped nanoparticles in each category are also included and personal perspectives on the future research directions in the synthesis of shaped metal nanoparticles are briefly summarized. This review is expected to provide a guideline in designing the strategy for the synthesis of shaped nanoparticles and analyzing the corresponding growth mechanism.     

Antibacterial mechanism of biogenic silver nanoparticles of Lactobacillus acidophilus

The development of reliable, eco-friendly protocol for the synthesis of nanomaterials is a challenging issue in the current nanotechnology. In the present study, we reported an environmentally benign and rapid method for biogenesis of silver nanoparticles using Gram-positive bacterium Lactobacillus acidophilus which acts both as reducing and capping agent. It was observed that the culture filtrate reduced silver ions into silver nanoparticles within 24 hrs of reaction time under room temperature. The UV–Vis spectrum shows the absorbance maximum at 434 nm, which is a characteristic of surface plasmon resonance of silver. X-ray diffraction analysis showed that the nanoparticles were of face-centred cubic crystalline structure. The presence of stable spherical-shaped silver nanoparticles in the size range of 4–50 nm was determined using the transmission electron microscopy analysis. Further, these nanoparticles showed effective antibacterial activity towards Klebsiella pneumoniae. The mechanism of the silver nanoparticle bactericidal activity is discussed in terms of its interaction with the cell membrane of bacteria by causing cytolysis and leakage of proteins and carbohydrates.     

Microwave assisted template synthesis of silver nanoparticles

Easier, less time consuming, green processes, which yield silver nanoparticles of uniform size, shape and morphology are of interest. Various methods for synthesis, such as conventional temperature assisted process, controlled reaction at elevated temperatures, and microwave assisted process have been evaluated for the kind of silver nanoparticles synthesized. Starch has been employed as a template and reducing agent. Electron microscopy, photon correlation spectroscopy and surface plasmon resonance have been employed to characterize the silver nanoparticles synthesized. Compared to conventional methods, microwave assisted synthesis was faster and provided particles with an average particle size of 12 nm. Further, the starch functions as template, preventing the aggregation of silver nanoparticles.     

Differential interaction of silver nanoparticles with cysteine

Understanding the characteristics of cysteine on a solid surface is an important issue in protein study and amino acid analysis. Therefore, cysteine was selected as a model biomolecule to study the interaction with plasmonic silver nanoparticles. In this study, we report the differential interaction of cysteine with silver nanoparticles synthesised by Lee and Meisel (using citrate as reductant), and modified Creighton (citrate and borohydride as reductant) methods. In Lee and Meisel's method, the red-shifting of silver plasmon resonance in the UV–vis spectra and the aggregation of the particles occurred owing to a decrease in stability of silver nanoparticles upon interaction with cysteine. In contrast, the other method did not cause any aggregation or significant spectral changes. The differential behaviour may be due to surface chemical changes on cysteine with pH, which plays a major role in the nanoparticle-biomolecule interaction. The synthesis of silver nanoparticles applying two sol gel methods followed by interactions with cysteine induces different functionalities on the nanoparticles, which may find specific applications in bio-sensing and drug delivery.