Development of an eco-friendly approach for biogenesis of silver nanoparticles using spores of Bacillus athrophaeus

The biological synthesis methods have been emerging as a promising new approach for production of nanoparticles due to their simplicity and non-toxicity. In the present study, spores of Bacillus athrophaeus were used to achieve the objective of developing a green synthesis method of silver nanoparticles. Enzyme assay revealed that the spores and their heat inactivated forms (microcapsules) were highly active and their enzymatic contents differed from the vegetative cells. Laccase, glucose oxidase, and alkaline phosphatase activities were detected in the dormant forms, but not in the vegetative cells. Although no nanoparticle was produced by active cells of B. athrophaeus, both spores and microcapsules were efficiently capable of reducing the silver ions (Ag⁺) to elemental silver (Ag⁰) leading to the formation of nanoparticles from silver nitrate (AgNO₃). The presence of biologically synthesized silver nanoparticles was determined by obtaining broad spectra with maximum absorbance at 400 nm in UV–visible spectroscopy. The X-ray diffraction analysis pattern revealed that the nanoscale particles have crystalline nature with various topologies, as confirmed by transmission electron microscopy (TEM). The TEM micrograph showed the nanocrystal structures with dimensions ranging from 5 to 30 nm. Accordingly, the spore mixture could be employed as a factory for detoxification of heavy metals and subsequent production of nanoparticles. This research introduces an environmental friendly and cost effective biotechnological process for the extracellular synthesis of silver nanoparticles using the bacterial spores.     

Mycoendophytes as efficient synthesizers of bionanoparticles: nanoantimicrobials,mechanism, and cytotoxicity

Mycoendophytes are the fungi that occur inside the plant tissues without exerting any negative impact on the host plant. They are most frequently isolated endophytes from the leaf, stem, and root tissues of various plants. Among all fungi, the mycoendophytes as biosynthesizer of noble metal nanoparticles (NPs) are less known. However, some reports showing efficient synthesis of metal nanoparticles, mainly silver nanoparticles and its remarkable antimicrobial activity against bacterial and fungal pathogens of humans and plants. The nanoparticles synthesized from mycoendophytes present stability, polydispersity, and biocompatibility. These are non-toxic to humans and environment, can be gained in an easy and cost-effective manner, have wide applicability and could be explored as promising candidates for a variety of biomedical, pharmaceutical, and agricultural applications. Mycogenic silver nanoparticles have also demonstrated cytotoxic activity against cancer cell lines and may prove to be a promising anticancer agent. The present review focuses on the biological synthesis of metal nanoparticles from mycoendophytes and their application in medicine. In addition, different mechanisms of biosynthesis and activity of nanoparticles on microbial cells, as well as toxicity of these mycogenic metal nanoparticles, have also been discussed.     

微生物合成纳米银的一般方法及产物性质鉴定与生产应用

纳米银具有独特的理化性质,在化学、医药等领域应用广泛,但使用化学和物理法生产纳米银毒性较强且污染严重,因此,微生物法成为了一种可供替代的绿色生产技术。近年来,微生物法合成纳米银的报道逐渐增多,对其反应条件和产物性质的研究趋于成熟,纳米银也开始与多个应用领域相结合。归纳现有微生物合成方法的规律,阐述产物的性质及应用,比较其与传统材料的优势与不足,将有助于推动微生物与纳米技术的结合与进步。基于国内外学者的报道和本课题组所开展的相关研究,本文对微生物法合成纳米银的一般检验手段和功能鉴定方法进行综述,并就纳米银的应用展开设想与讨论,以期为微生物法合成纳米银的深入研究和优化改进提供参考。     

Novel microbial route to synthesize silver nanoparticles using spore crystal mixture of Bacillus thuringiensis

Metallic nanoparticles are traditionally synthesized by wet chemical techniques, where the chemicals used are often toxic and flammable. In the present study, the spore crystal mixture of Bacillus thuringiensis was used for the synthesis of silver nanoparticles. Nanoparticles were characterized using UV-Vis absorption spectroscopy, XRD and TEM. X-ray diffraction and TEM analysis showed the average particle size of 15 nm and mixed (cubic and hexagonal) structure. This is for the first time that any bacterial spore crystal mixture was used for the synthesis of nanoparticles. Further, these biologically synthesized nanoparticles were found to be highly toxic against different multi drug resistant human pathogenic bacteria.     

Upregulation of Metallothioneins After Exposure of Cultured Primary Astrocytes to Silver Nanoparticles

To test for the prolonged consequences of a short transient exposure of astrocytes to silver nanoparticles (AgNP), cultured primary astrocytes were incubated for 4 h in the presence of AgNP and the cell viability as well as various metabolic parameters were investigated during a subsequent incubation in AgNP-free medium. Acute exposure of astrocytes to AgNP led to a concentration-dependent increase in the specific cellular silver content to up to 46 nmol/mg protein, but did not compromise cell viability. During a subsequent incubation of the cells in AgNP-free medium, the cellular silver content of AgNP-treated astrocytes remained almost constant for up to 7 days. The cellular presence of AgNP did neither induce any delayed cell toxicity nor were alterations in cellular glucose consumption, lactate production or in the cellular ratio of glutathione to glutathione disulfide observed. However, Western blot analysis and immunocytochemical staining revealed that AgNP-treated astrocytes strongly upregulated the expression of metallothioneins. These results demonstrate that a prolonged presence of accumulated AgNP does not compromise the viability and the basal metabolism of cultured astrocytes and suggest that the upregulation of metallothioneins may help to prevent silver-mediated toxicity that could be induced by AgNP-derived silver ions.     

The effect of temperature on antibacterial activity of biosynthesized silver nanoparticles

The purpose of this study was the evaluation of two different temperatures on antibacterial activity of the biosynthesized silver nanoparticles. 38 silver nanoparticles-producing bacteria were isolated from soil and identified. Biosynthesis of silver nanoparticles by these bacteria was verified through visible light spectrophotometry. Two strains were relatively active for production of silver nanoparticles. These strains were subjected for molecular identification and recognized as Bacillus sp. and Acinetobacter schindleri. In the present study, the effect of temperatures was evaluated on structure and antimicrobial properties of the silver nanoparrticles by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis and antimicrobial Agar well diffusion methods. The silver nanoparticles showed antibacterial activity against all the pathogenic bacteria; however, this property was lost after treatment of the silver nanoparticles by high temperatures (100 and 300 °C). TEM images showed that the average sizes of heated silver nanoparticles were >100 nm. However, these were <100 nm for non-heated silver nanoparticles. Although, XRD patterns showed the crystalline structure of heated silver nanoparticles, their antibacterial activities were less. This was possible because of the sizes and accordingly less penetration of the particles into the bacterial cells. In addition, elimination of the capping agents by heat might be considered another reason.     

Bactericidal effect of silver nanoparticles against multidrug-resistant bacteria

Infections caused by drug-resistant microorganisms result in significant increases in mortality, morbidity, and cost related to prolonged treatments. The antibacterial activity of silver nanoparticles against some drug-resistant bacteria has been established, but further investigation is needed to determine whether these particles could be an option for the treatment and prevention of drug-resistant microbial infections. Hence, we challenged different drug-resistant pathogens of clinical importance (multidrug-resistant Pseudomonas aeruginosa, ampicillin-resistant Escherichia coli O157:H7 and erythromycin-resistant Streptococcus pyogenes) with a suspension of silver nanoparticles. By means of a luciferase-based assay, it was determined that silver nanoparticles (1) inactivate a panel of drug-resistant and drug-susceptible bacteria (Gram positive and Gram negative), (2) exert their antibacterial activity through a bactericidal rather than bacteriostatic mechanism, and (3) inhibit the bacterial growth rate from the time of first contact between the bacteria and the nanoparticles. Additionally, strains with a resistant phenotype to silver nanoparticle were developed and used to explore the bactericidal mode of action of silver nanoparticles. Through a Kirby–Bauer test, it was shown that silver nanoparticles’ general mechanism of bactericidal action is based on inhibition of cell wall synthesis, protein synthesis mediated by the 30s ribosomal subunit, and nucleic acid synthesis. Our data suggest that silver nanoparticles are effective broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for use in pharmaceutical products and medical devices that may help to prevent the transmission of drug-resistant pathogens in different clinical environments.     

Crystallization of silver through reduction process using Elaeis guineensis biosolid extract

This study presents a special, economically valuable, unprecedented eco-friendly green process for the synthesis of silver nanoparticles. The silver nanoparticles were obtained from a waste material with oil palm biosolid extract as the reducing agent. The use of the oil palm biosolid extract for the nanoparticle synthesis offers the benefit of amenability for large-scale production. An aqueous solution of silver (Ag(+) ) ions was treated with the oil palm biosolid extract for the formation of Ag nanoparticles. The nanometallic dispersion was characterized by surface plasmon absorbance measuring 428 nm. Transmission electron microscopy showed the formation of silver nanoparticles in the range of 5-50 nm. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction analysis of the freeze-dried powder confirmed the formation of metallic silver nanoparticles. Moreover, Fourier Transform Infrared Spectroscopy provided evidence of phenolics or proteins as the biomolecules that were likely responsible for the reduction and capping agent, which helps to increase the stability of the synthesized silver nanoparticles. In addition, we have optimized the production with various parameters.     

Characterization of silver nanoparticles synthesized by using marine isolate Streptomyces albidoflavus

Silver nanoparticles production by the green chemistry approach was investigated using an isolated marine actinomycetes strain. The isolated strain was identified as Streptomyces albidoflavus based on chemotaxonomic and ribotyping properties. The strain revealed production of silver nanoparticles both extracellular and intracellularly. Surface Plasmon Resonance analysis with the function of time revealed that particle synthesis by this strain is reaction time dependent. The produced particles were spherical shaped and monodispersive in nature and showed a single surface plasmon resonance peak at 410 nm. Size distribution histograms indicated production of 10-40- nm-size nanoparticles with a mean size of 14.5 nm. FT-IR spectra of nanopartilces showed N-H, C-H, and C-N stretching vibrations, denoting the presence of amino acid/ peptide compounds on the surface of silver nanoparticles produced by S. albidoflavus. Synthesized nanoparticles revealed a mean negative zeta potential and electrophoretic mobility of -8.5 mV and -0.000066 cm2/Vs, respectively. The nanoparticles produced were proteinaceous compounds as capping agents with -8.5 mV zeta potential and revealed antimicrobial activity against both Gram-negative and -positive bacterial strains. Owing to their small size, these particles have greater impact on industrial application spectra.     

Biosynthesis of silver nanoparticles using aqueous extract from the compactin producing fungal strain

In the present study, an eco-friendly process for the synthesis of nanomaterials using a fungus, Penicillium brevicompactum WA 2315 has been attempted. The fungus has been previously utilized for compactin production. Supernatant of seed culture was used for the biosynthesis of silver nanoparticles. The aqueous silver ions were reduced to silver metal nanoparticles when treated with the fungal supernatant. After 72 h of treatment, silver nanoparticles obtained were in the range of 23–105 nm as obtained from TEM. The nanoparticles were characterized by UV, FTIR, SEM, TEM and XRD. The use of supernatant of the seed media of the said fungus opens up the exciting possibility of rational strategy of biosynthesis of nanomaterials.     

Lactic acid bacteria as reducing and capping agent for the fast and efficient production of silver nanoparticles

There is a growing demand for silver-based biocides, including both ionic silver forms and metallic nanosilver. The use of metallic nanosilver, typically chemically produced, faces challenges including particle agglomeration, high costs, and upscaling difficulties . Additionally, there exists a need for the development of a more eco-friendly production of nanosilver. In this study, Gram-positive and Gram-negative bacteria were utilized in the non-enzymatic production of silver nanoparticles via the interaction of silver ions and organic compounds present on the bacterial cell. Only lactic acid bacteria, Lactobacillus spp., Pediococcus pentosaceus, Enterococcus faecium, and Lactococcus garvieae, were able to reduce silver. The nanoparticles of the five best producing Lactobacillus spp. were examined more into detail with transmission electron microscopy. Particle localization inside the cell, the mean particle size, and size distribution were species dependent, with Lactobacillus fermentum having the smallest mean particle size of 11.2 nm, the most narrow size distribution, and most nanoparticles associated with the outside of the cells. Furthermore, influence of pH on the reduction process was investigated. With increasing pH, silver recovery increased as well as the reduction rate as indicated by UV–VIS analyses. This study demonstrated that Lactobacillus spp. can be used for a rapid and efficient production of silver nanoparticles.     

Morphological alterations in erythrocytes treated with silver nanoparticles biomineralized by marine sediment-derived Bacillus sp. VITSSN01

Biomineralization-inspired preparation of nanoparticles by marine microorganisms is in the limelight of modern nanotechnology. In recent years, the use of marine microorganisms for the synthesis of nanoparticles has been gaining importance due to the simplicity and eco-friendliness of the approach. Here we describe the synthesis of silver nanoparticles using halotolerant Bacillus sp. isolated from the southern coastal waters of India. Our selective and enriched isolation technique resulted in the isolation of a silver nitrate-resistant novel marine Bacillus sp. isolated from sediments collected at Ennore Port, Chennai, India. The strain was characterized by the polyphasic taxonomic approach, and phenotypic and phylogenetic analysis identified the strain as Bacillus sp. VITSSN01. The resistant strain was further assayed for the synthesis of silver nanoparticles and its biological activity evaluated. Nanoparticles were synthesized under optimized nutritional and cultural conditions with shaking and the production continuously monitored. The nanoparticles thus produced were then characterized by atomic force microscopy, X-ray diffraction, Fourier transform-infrared spectrophotometer and transmission electron microscopy. The mean particle size was 46 nm. Hemotological toxicity of nanoparticles is very severe form and less studied. We therefore checked the synthesized silver nanoparticles for toxicity against erythrocytes and found that the silver nanoparticles exhibited moderate hemolytic activity against human erythrocytes, with a half maximal effective concentration (EC₅₀) value of 60 μg/ml. Microscopic studies of the treated erythrocytes showed slight structural perturbations. The results of our study strongly suggest that marine microorganisms could be a potential source for the rapid and eco-friendly synthesis of nanoparticles.     

Rapid biological synthesis of silver nanoparticles using plant leaf extracts

Five plant leaf extracts (Pine, Persimmon, Ginkgo, Magnolia and Platanus) were used and compared for their extracellular synthesis of metallic silver nanoparticles. Stable silver nanoparticles were formed by treating aqueous solution of AgNO₃ with the plant leaf extracts as reducing agent of Ag⁺ to Ag⁰. UV-visible spectroscopy was used to monitor the quantitative formation of silver nanoparticles. Magnolia leaf broth was the best reducing agent in terms of synthesis rate and conversion to silver nanoparticles. Only 11 min was required for more than 90% conversion at the reaction temperature of 95 °C using Magnolia leaf broth. The synthesized silver nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and particle analyzer. The average particle size ranged from 15 to 500 nm. The particle size could be controlled by changing the reaction temperature, leaf broth concentration and AgNO₃ concentration. This environmentally friendly method of biological silver nanoparticles production provides rates of synthesis faster or comparable to those of chemical methods and can potentially be used in various human contacting areas such as cosmetics, foods and medical applications.     

Rapid biosynthesis of PVP coated silver nanoparticles by <Emphasis Type="Italic">Kocuria rosea</Emphasis> and their antimicrobial activity

The need for more effective antimicrobial agent and propitious application of nanotechnology in therapeutics and diagnostics has prompted the research on ecofriendly synthesis of silver nanoparticles. The objective of present study was to investigate the antibacterial and antifungal activity of biologically synthesized silver nanoparticles. The silver nanoparticles were synthesized by extracellular method, using soil bacteria Kocuria rosea. The synthesized silver nanoparticles were characterized by UV-Visible spectroscopy, X-ray diffractometry (XRD), transmission electron microscopy (TEM) and fourier transformation infrared spectroscopy (FTIR). On the basis of TEM analysis, the synthesized nanoparticles were found to be spherical with an average size of 30–50 nm. The biologically synthesized silver nanoparticles showed significant antimicrobial activity against pathogens.     

Photochemical Synthesis and Multiphoton Luminescence of Monodisperse Silver Nanocrystals

A rapid, photochemical solution-phase synthesis has been developed for the production of monodisperse, nanometer-sized silver particles. The stabilizer used in the synthesis can be used to control the average diameter of the particles over a range from 1 to 7 nm. The same reaction mixture can also be employed to deposit patterns of nanoparticles with a laser via multiphoton absorption. The particles exhibit strong multiphoton absorption-induced luminescence when irradiated with 800-nm light, allowing emission from single nanoparticles to be observed readily.     

Soybean protein: A natural source for the production of green silver nanoparticles

The ethnopharmacological approach to the production of nanoparticles is directly related to the creation of an important symbiosis between nanoscience and medical science. Production of nanoparticles under ecofriendly conditions is of significance to address growing concerns on the overall toxicity of nanoparticles for medical and biotechnological applications. The present investigation demonstrates silver nanoparticles production capabilities of a miracle bean soybean Glycine max. We found that a single protein of soybean with a molecular weight of 51 kDa stabilizes the newly formed silver nanoparticles. The electroeluted protein has confirmed the bioreduction property of silver ions.     

Antimicrobial Activities of Silver Nanoparticles Synthesized by Using Water Extract of Arnicae anthodium

Green synthesis of nanoparticles has gained significant importance in recent years and has become the one of the most preferred methods. Also, green synthesis of nanoparticles is valuable branch of nanotechnology. Plant extracts are eco-friendly and can be an economic option for synthesis of nanoparticles. This study presents method the synthesis of silver nanoparticles using water extract of Arnicae anthodium. Formation of silver nanoparticles was confirmed by UV–visble spectroscopy, Fourier transform infrared spectroscopy and total reflection X-ray fluorescence analysis. The morphology of the synthesized silver nanoparticles was verified by SEM–EDS. The obtained silver nanoparticles were used to study their antimicrobial activity.     

Synthesis of Silver Nanoparticles Using Callus Extract of Carica papaya — A First Report

This is the first report of synthesis of silver nanoparticles by using callus extract of Carica papaya. MS medium supplemented with the growth hormones, 2.0 mg l^?1 IBA and 0.5 mg l^?1 BAP was found to be more suitable for the induction of callus and multiple shoots in papaya. The extract of callus obtained by grinding showed ability of synthesis of silver nanoparticles when treated with silver nitrate (1 mM). The formation of brown colour in the reaction mixture indicates the synthesis of silver nanoparticles. The further detection and characterization of these synthesized silver nanoparticles was carried by spectrophotometry. FTIR spectrum analysis showed peaks between 1000–2000 cm^?1 which confirmed the presence of proteins and other ligands required for the synthesis and stabilization of silver nanoparticles. SEM micrograph confirmed the synthesis of spherical silver nanoparticles in the size range of 60–80 nm.     

Silver nanoparticles as a new generation of antimicrobials

Silver has been in use since time immemorial in the form of metallic silver, silver nitrate, silver sulfadiazine for the treatment of burns, wounds and several bacterial infections. But due to the emergence of several antibiotics the use of these silver compounds has been declined remarkably. Nanotechnology is gaining tremendous impetus in the present century due to its capability of modulating metals into their nanosize, which drastically changes the chemical, physical and optical properties of metals. Metallic silver in the form of silver nanoparticles has made a remarkable comeback as a potential antimicrobial agent. The use of silver nanoparticles is also important, as several pathogenic bacteria have developed resistance against various antibiotics. Hence, silver nanoparticles have emerged up with diverse medical applications ranging from silver based dressings, silver coated medicinal devices, such as nanogels, nanolotions, etc.