Biosynthesis of extracellular and intracellular gold nanoparticles by Aspergillus fumigatus and A. flavus

Green chemistry is a boon for the development of safe, stable and ecofriendly nanostructures using biological tools. The present study was carried out to explore the potential of selected fungal strains for biosynthesis of intra- and extracellular gold nanostructures. Out of the seven cultures, two fungal strains (SBS-3 and SBS-7) were selected on the basis of development of dark pink colour in cell free supernatant and fungal beads, respectively indicative of extra- and intracellular gold nanoparticles production. Both biomass associated and cell free gold nanoparticles were characterized using X-ray diffractogram (XRD) analysis and transmission electron microscopy (TEM). XRD analysis confirmed crystalline, face-centered cubic lattice of metallic gold nanoparticles along with average crystallite size. A marginal difference in average crystallite size of extracellular (17.76 nm) and intracellular (26 and 22 nm) Au-nanostructures was observed using Scherrer equation. In TEM, a variety of shapes (triangles, spherical, hexagonal) were observed in both extra- and intracellular nanoparticles. 18S rRNA gene sequence analysis by multiple sequence alignment (BLAST) indicated 99 % homology of SBS-3 to Aspergillus fumigatus with 99 % alignment coverage and 98 % homology of SBS-7 to Aspergillus flavus with 98 % alignment coverage respectively. Native-PAGE and activity staining further confirmed enzyme linked synthesis of gold nanoparticles.     

Novel polyhedral gold nanoparticles: green synthesis,optimization and characterization by environmental isolate of Acinetobacter sp. SW30

Gold nanoparticles have enormous applications in cancer treatment, drug delivery and nanobiosensor due to their biocompatibility. Biological route of synthesis of metal nanoparticles are cost effective and eco-friendly. Acinetobacter sp. SW 30 isolated from activated sewage sludge produced cell bound as well as intracellular gold nanoparticles when challenged with HAuCl₄ salt solution. We first time report the optimization of various physiological parameters such as age of culture, cell density and physicochemical parameters viz HAuCl₄ concentration, temperature and pH which influence the synthesis of gold nanoparticles. Gold nanoparticles thus produced were characterized by various analytical techniques viz. UV–Visible spectroscopy, X-ray diffraction, cyclic voltammetry, transmission electron microscopy, selected area electron diffraction, high resolution transmission electron microscopy, environmental scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and dynamic light scattering. Polyhedral gold nanoparticles of size 20 ± 10 nm were synthesized by 24 h grown culture of cell density 2.4 × 10⁹ cfu/ml at 50 °C and pH 9 in 0.5 mM HAuCl₄. It was found that most of the gold nanoparticles were released into solution from bacterial cell surface of Acinetobacter sp. at pH 9 and 50 °C.     

Microbial synthesis of gold nanoparticles using the fungus <Emphasis Type="Italic">Penicillium brevicompactum</Emphasis> and their cytotoxic effects against mouse mayo blast cancer C<Subscript>2</Subscript>C<Subscript>12</Subscript> cells

Microorganisms, their cell filtrates, and live biomass have been utilized for synthesizing various gold nanoparticles. The shape, size, stability as well as the purity of the bio synthesized nanoparticles become very essential for application purpose. In the present study, gold nanoparticles have been synthesized from the supernatant, live cell filtrate, and biomass of the fungus Penicillium brevicompactum. The fungus has been grown in potato dextrose broth which is also found to synthesize gold nanoparticles. The size of the particles has been investigated by Bio-TEM before purification, following purification and after storing the particles for 3 months under refrigerated condition. Different characterization techniques like X-ray diffraction, Fourier transform infrared spectroscopy, and UV–visible spectroscopy have been used for analysis of the particles. The effect of reaction parameters such as pH and concentration of gold salt have also been monitored to optimize the morphology and dispersity of the synthesized gold nanoparticles. A pH range of 5 to 8 has favored the synthesis process whereas increasing concentration of gold salt (beyond 2 mM) has resulted in the formation of bigger sized and aggregated nanoparticles. Additionally, the cytotoxic nature of prepared nanoparticles has been analyzed using mouse mayo blast cancer C₂C₁₂ cells at different time intervals (24, 48, and 72 h) of incubation period. The cells are cultivated in Dulbecco’s modified Eagle’s medium supplemented with fetal bovine serum with antibiotics (streptopenicillin) at 37°C in a 5% humidified environment of CO₂. The medium has been replenished every other day, and the cells are subcultured after reaching the confluence. The viability of the cells is analyzed with 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method.     

Mycogenesis of gold nanoparticles using a phytopathogen <Emphasis Type="Italic">Alternaria alternata</Emphasis>

The development of an eco-friendly and reliable process for the synthesis of gold nanomaterials (AuNPs) using microorganisms is gaining importance in the field of nanotechnology. In the present study, AuNPs have been synthesized by bio-reduction of chloroauric acid (HAuCl₄) using the fungal culture filtrate (FCF) of Alternaria alternata. The synthesis of the AuNPs was monitored by UV–visible spectroscopy. The particles thereby obtained were characterized by UV, dynamic light scattering (DLS), X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). Energy-dispersive X-ray study revealed the presence of gold in the nanoparticles. Fourier transform infrared spectroscopy confirmed the presence of a protein shell outside the nanoparticles which in turn also support their stabilization. Treatment of the fungal culture filtrate with aqueous Au⁺ ions produced AuNPs with an average particle size of 12 ± 5 nm. This proposed mechanistic principal might serve as a set of design rule for the synthesis of nanostructures with desired architecture and can be amenable for the large scale commercial production and technical applications.     

Biosynthesis of fluorescent gold nanoparticles using an edible freshwater red alga,Lemanea fluviatilis (L.) C.Ag. and antioxidant activity of biomatrix loaded nanoparticles

Biosynthesis of gold nanoparticles has been accomplished via reduction of an aqueous chloroauric acid solution with the dried biomass of an edible freshwater epilithic red alga, Lemanea fluviatilis (L.) C.Ag., as both reductant and stabilizer. The synthesized nanoparticles were characterized by UV–visible, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), and dynamic light scattering (DLS) studies. The UV–visible spectrum of the synthesized gold nanoparticles showed the surface plasmon resonance (SPR) at around 530 nm. The powder XRD pattern furnished evidence for the formation of face-centered cubic structure of gold having average crystallite size 5.9 nm. The TEM images showed the nanoparticles to be polydispersed, nearly spherical in shape and have sizes in the range 5–15 nm. The photoluminescence spectrum of the gold nanoparticles excited at 300 nm showed blue emission at around 440 nm. Gold nanoparticles loaded within the biomatrix studied using a modified 2,2-diphenyl-1-picrylhydrazyl (DPPH) method exhibited pronounced antioxidant activity.     

Tansy fruit mediated greener synthesis of silver and gold nanoparticles

In this paper we have reported the green synthesis of silver (AgNPs) and gold (AuNPs) nanoparticles by reduction of silver nitrate and chloroauric acid solutions, respectively, using fruit extract of Tanacetum vulgare; commonly found plant in Finland. The process for the synthesis of AgNPs and AuNPs is rapid, novel and ecofriendly. Formation of the AgNPs and AuNPs were confirmed by surface plasmon spectra using UV–Vis spectrophotometer and absorbance peaks at 452 and 546 nm. Different tansy fruit extract concentration (TFE), silver and gold ion concentration, temperature and contact times were experimented in the synthesis of AgNPs and AuNPs. The properties of prepared nanoparticles were characterized by TEM, XRD, EDX and FTIR. Finally zeta potential values at various pH were analyzed along with corresponding SPR spectra.     

Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts

Leaf extracts of two plants, Magnolia kobus and Diopyros kaki, were used for ecofriendly extracellular synthesis of metallic gold nanoparticles. Stable gold nanoparticles were formed by treating an aqueous HAuCl₄ solution using the plant leaf extracts as reducing agents. UV–visible spectroscopy was used for quantification of gold nanoparticle synthesis. Only a few minutes were required for >90% conversion to gold nanoparticles at a reaction temperature of 95 °C, suggesting reaction rates higher or comparable to those of nanoparticle synthesis by chemical methods. The synthesized gold nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and particle analysis using a particle analyzer. SEM and TEM images showed that a mixture of plate (triangles, pentagons, and hexagons) and spherical structures (size, 5–300 nm) were formed at lower temperatures and leaf broth concentrations, while smaller spherical shapes were obtained at higher temperatures and leaf broth concentrations.     

Extracellular synthesis of gold bionanoparticles by <Emphasis Type="Italic">Nocardiopsis</Emphasis> sp. and evaluation of its antimicrobial,antioxidant and cytotoxic activities

Advancement of biological process for the synthesis of bionanoparticles is evolving into a key area of research in nanotechnology. The present study deals with the biosynthesis, characterization of gold bionanoparticles by Nocardiopsis sp. MBRC-48 and evaluation of their antimicrobial, antioxidant and cytotoxic activities. The gold bionanoparticles obtained were characterized by UV–visible spectroscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and transmission electron microscopy (TEM). The synthesized gold bionanoparticles were spherical in shape with an average of 11.57 ± 1.24 nm as determined by TEM and dynamic light scattering (DLS) particle size analyzer, respectively. The biosynthesized gold nanoparticles exhibited good antimicrobial activity against pathogenic microorganisms. It showed strong antioxidant activity as well as cytotoxicity against HeLa cervical cancer cell line. The present study demonstrated the potential use of the marine actinobacterial strain of Nocardiopsis sp. MBRC-48 as an important source for gold nanoparticles with improved biomedical applications including antimicrobial, antioxidant as well as cytotoxic agent.     

Depth distribution of photosynthetic pigments and diatoms in the sediments of a microtidal fjord

The depth distribution of photosynthetic pigments and benthic marine diatoms was investigated in late spring at three different sites on the Swedish west coast. At each site, sediment cores were taken at six depths (7–35 m) by scuba divers. It was hypothesized that (1) living benthic diatoms constitute a substantial part of the benthic microflora even at depths where the light levels are <1% of the surface irradiance, and (2) the changing light environment along the depth gradient will be reflected in (a) the composition of diatom assemblages, and (b) different pigment ratios. Sediment microalgal communities were analysed using epifluorescence microscopy (to study live cells), light microscopy and scanning electron microscopy (diatom preparations), and HPLC (photosynthetic pigments). Pigments were calculated as concentrations (mg m^–2) and as ratios relative to chlorophyll a. Hypothesis (1) was accepted. At 20 m, the irradiance was 0.2% of surface irradiance and at 7 m, 1%. Living (epifluorescent) benthic diatoms were found down to 20 m at all sites. The cell counts corroborated the diatom pigment concentrations, decreasing with depth from 7 to 25 m, levelling out between 25 and 35 m. There were significant positive correlations between chlorophyll a and living (epifluorescent) benthic diatoms and between the diatom pigment fucoxanthin and chlorophyll a. Hypothesis (2) was only partly accepted because it could not be shown that light was the main environmental factor. A principal component analysis on diatom species showed that pelagic forms characterized the deeper locations (25–35 m), and epipelic–epipsammic taxa the shallower sites (7–20 m). Redundancy analyses showed a significant relationship between diatom taxa and environmental factors – temperature, salinity, and light intensities explained 57% of diatom taxa variations.     

Luminescence properties of a nanoporous freshwater diatom

Freshwater diatom frustules show special optical properties. In this paper we observed luminescence properties of the freshwater diatom Cyclotella meneghiniana. To confirm the morphological properties we present scanning electron microscopy (SEM) images. X‐ray diffraction (XRD) studies were carried out to visualize the structural properties of the frustules, confirming that silica present in diatom frustules crystallizes in an α‐quartz structure. Study of the optical properties of the silica frustules of diatoms using ultra‐violet‐visible (UV‐vis) spectroscopy and photoluminescence spectroscopy confirmed that the diatom C. meneghiniana shows luminescence in the blue region of the electromagnetic spectrum when irradiated with UV light. This property of diatoms can be exploited to obtain many applications in day‐to‐day life. Also, using time‐resolved photoluminescence spectroscopy (TRPL) it was confirmed that this species of diatom shows bi‐exponential decay. Copyright © 2011 John Wiley & Sons, Ltd.     

Supramolecular organization of fucoxanthin–chlorophyll proteins in centric and pennate diatoms

Fucoxanthin–chlorophyll proteins (FCP) are the major light-harvesting proteins of diatom algae, a major contributor to marine carbon fixation. FCP complexes from representatives of centric (Cyclotella meneghiniana) and pennate (Phaeodactylum tricornutum) diatoms were prepared by sucrose gradient centrifugation and studied by means of electron microscopy followed by single particle analysis. The oligomeric FCP from a centric diatom were observed to take the form of unusual chain-like or circular shapes, a very unique supramolecular assembly for such antennas. The existence of the often disputed oligomeric form of FCP in pennate diatoms has been confirmed. Contrary to the centric diatom FCP, pennate diatom FCP oligomers are very similar to oligomeric antennas from related heterokont (Stramenopila) algae. Evolutionary aspects of the presence of novel light-harvesting protein arrangement in centric diatoms are discussed.     

Investigation of Gold and Silver Nanoparticles on Absorption Heating and Scattering Imaging

Efficient conversion of absorbed light to heat energy and strong scattering by gold and silver nanoparticles suggest these nanoparticles as the agents of heating and imaging. Absorption efficiency and scattering efficiency of gold and silver nanoparticles were studied through numerical simulation using the discrete dipole approximation method. This study shows that the size of gold and silver nanoparticles can effect gold and silver nanoparticles’ absorption efficiency and scattering efficiency. The gold nanoparticle is found to possess the maximum absorption efficiency when the size of gold nanoparticle is 50 nm and the incident wavelength is 540 nm, and the increasing scattering efficiency with the increasing size of gold nanoparticle in the medium, and refractive index of the medium is around 1.33. However, the silver nanoparticle owns the maximum absorption efficiency when the size of silver nanoparticle is 20 nm and the incident wavelength is 396 nm, and the maximum scattering efficiency when the size of silver nanoparticle is 30 nm and the incident wavelength is 410 nm in the same medium. The conditions for achieving the maximum adsorption efficiency and scattering efficiency of gold and silver nanoparticle can be used for heating and imaging using visible and near-infrared light.     

Dominance of microflagellates over diatoms in the Antarctic areas of deep vertical mixing and krill concentrations

Phytoplankton data obtained during six summer Polish expeditionsto the Antarctic Peninsula area, are compared with concurrentlyrecorded data on water column stabilities and krill abundance.The results show that flagellates (1.5–20 µm) arenumerically dominant over diatoms in the areas of deep verticalmixing and/or extensive krill concentrations. Of 102 stationsdominated by flagellates, 85 (83.3%) are located in a well mixedwater column (>100 m) and correspond to a mean krill densityof 15–346 t Nm^–2. In the same areas, estimated flagellatecarbon biomass exceeds diatom carbon. On the other hand, ofthe 40 stations dominated by diatoms, 36 (90%) are located inareas of increased water column stability (upper mixed layerof 10–50 m) and correspond to a low mean krill biomassof 0.34–4.6 t Nm^–2. Positive correlations of flagellateto diatom (F:D) cell number ratios with the depth of the uppermixed layer suggest light limitation of diatom growth and anincreased sinking rate of diatoms relative to flagellates inthe areas of deep vertical mixing. The relationship of the F:Dratio with krill abundance suggests that krill prefer feedingon diatoms and are less efficient in grazing particles of thesize of microflagellates (<20 µm). Flagellates exceeddiatoms in an unstable water column when the phytoplankton populationsare low; both algal groups increase in numbers with growingstability. The results provide field evidence that deep verticalmixing and krill grazing create conditions for the dominanceof flagellates over diatoms. Both factors acting together arelikely to suppress diatom blooms in the Antarctic.     

Changes in the condition of photosynthetic apparatus of a diatom alga <Emphasis Type="Italic">Thallassiosira weisflogii</Emphasis> during photoadaptation and photodamage

Two populations of a diatom alga Thallassiosira weisflogii were grown at photon flux densities (PFD) of 0.8 and 8 μmol/(m² s). For both diatom populations, the recovery of chlorophyll fluorescence parameters (F ₀, F _m, F _v/F _m, and NPQ) was monitored after nondestructive irradiation by visible light at PFD of 40 μmol/(m² s) and after high-intensity irradiation by visible light (1000–4000 μmol/(m² s)). The exposure of diatoms to PFD of 40 μmol/(m² s)—higher than PFD used for algal growth but still nondamaging to photosynthetic apparatus—induced nonphotochemical quenching (NPQ), which was stronger in algae grown at higher PFD (8 μmol/(m² s)) than in algae grown at low light. After irradiation with high-intensity light, the recovery of chlorophyll fluorescence parameters was more pronounced in algae grown at elevated PFD level. During short-term irradiation of diatoms with high-intensity visible light (1000 μmol/(m² s)), a stronger NPQ was observed in the culture adapted to high irradiance. After the treatment of algae with dithiothreitol (an inhibitor of carotenoid deepoxidase in the diadinoxanthin cycle) or NH₄Cl (an agent abolishing the proton gradient at thylakoid membranes), a short exposure of algae to PFD of 40 μmol/(m² s) induced hardly any nonphotochemical quenching. The results indicate the dominant contribution of xanthophyll cycle carotenoids to energy-dependent quenching.     

Biogenic synthesis of floral-shaped gold nanoparticles using a novel strain,Talaromyces flavus

A biogenic route was adopted towards the synthesis of gold nanoparticles using the extract of a novel strain, Talaromyces flavus. Reduction of chloroauric acid by the fungal extract resulted in the production of gold nanoparticle, which was further confirmed by the concordant results obtained from UV–visible spectroscopy, energy dispersive spectroscopy (EDS), and dynamic light scattering (DLS) analysis. Morphology and the crystal nature of the synthesized nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and selected area electron diffraction (SAED). A direct correlation was observed between nanoparticle formation and the concentration of reducing agent present in the fungal extract. The time-dependent kinetic study revealed that the bioreduction process follows an autocatalytic reaction. Crystalline, irregular, and mostly flower-shaped gold nanoparticles with a mean hydrodynamic radius of 38.54?±?10.34 nm were obtained. pH played a significant role on production of mono-dispersed nanoparticle. FTIR analysis partially deciphered the involvement of –NH₂, ?SH, and –CO groups as the probable molecules in the bio-reduction and stabilization process. Compared to the conventional methods, a time-resolved, green, and economically viable method for floral-shaped nanoparticle synthesis was developed.     

Antimicrobial activity of metal and non-metallic nanoparticles from Cyperus rotundus root extract on infectious disease causing pathogens

In the present study, gold nanoparticles (CRnp) has been prepared using aqueous extract of Cyperus rotundus root at room temperature, sunlight, sonication, microwave oven heating and hot air oven method. Effect of concentration variation was studied using microwave-assisted synthesis. Grayish pink colour gold nanoparticles were formed within 5 s in microwave-assisted synthesis. Preliminary phytochemical screening showed the presence of alkaloids, protein and phenolic groups. These metabolites may be the responsible for the formation of gold nanoparticles. Reduced graphene oxide (CRrGO) was prepared using refluxing method and nano composite (CRNC) was prepared using equal ratio (1:1) of CRnp and CRrGO under homogenization method. The prepared CRnp, CRrGO and CRNC were characterized by spectroscopic techniques such as UV–visible spectroscopy, FTIR, XRD, Raman spectroscopy and FESEM. Thermal stability analysis of the CRrGO was carried out using TGA. FESEM results revealed the synthesized CRnp to be spherical in nature with average diameter 15 nm. CRrGO showed flake-like structures with few layers which was further confirmed by FESEM and Raman spectroscopy. The FESEM image of CRNC clearly portrays CRnp to be strongly bound to the surface of CRrGO. Anti-bacterial activity of the synthesized CRnp, CRrGO, CRNC and CRa synthesized nanoparticles to be active against gram negative and gram positive bacteria.     

Gold Nanoparticles Attenuates Antimycin A-Induced Mitochondrial Dysfunction in MC3T3-E1 Osteoblastic Cells

Gold nanoparticles have shown promising biological applications due to their unique properties. Understanding the interaction mechanisms between nanomaterials and biological cells is important for the control and manipulation of these interactions for biomedical applications. In the present study, we investigated the effects of gold nanoparticles on the differentiation of osteoblastic MC3T3-E1 cells and antimycin A-induced mitochondrial dysfunction. The results showed that gold nanoparticles (5, 10, and 20 nm) caused a significant elevation of cell growth, alkaline phosphatase activity, collagen synthesis, and osteocalcin content in the cells (P?<?0.05). Moreover, pretreatment with gold nanoparticles prior to antimycin A exposure significantly reduced antimycin A-induced cell damage by preventing mitochondrial membrane potential dissipation, complex IV inactivation, ATP loss, cytochrome c release, cardiolipin peroxidation, and reactive oxygen species generation. Taken together, our study indicated that gold nanoparticles may improve the differentiation and have protective effects on mitochondrial dysfunction of osteoblastic cells.     

Synthesis of Silver and Gold Nanoparticles Using Cashew Nut Shell Liquid and Its Antibacterial Activity Against Fish Pathogens

This study reveals a green process for the production of multi-morphological silver (Ag NPs) and gold (Au NPs) nanoparticles, synthesized using an agro-industrial residue cashew nut shell liquid. Aqueous solutions of Ag⁺ ions for silver and chloroaurate ions for gold were treated with cashew nut shell extract for the formation of Ag and Au NPs. The nano metallic dispersions were characterized by measuring the surface plasmon absorbance at 440 and 546 nm for Ag and Au NPs. Transmission electron microscopy showed the formation of nanoparticles in the range of 5–20 nm for silver and gold with assorted morphologies such as round, triangular, spherical and irregular. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analyses of the freeze-dried powder confirmed the formation of metallic Ag and Au NPs in crystalline form. Further analysis by Fourier transform infrared spectroscopy provided evidence for the presence of various biomolecules, which might be responsible for the reduction of silver and gold ions. The obtained Ag and Au NPs had significant antibacterial activity, minimum inhibitory concentration and minimum bactericidal concentration on bacteria associated with fish diseases.     

The paths of Andrew A. Benson: a radio-autobiography

Among marine phytoplankton groups, diatoms span the widest range of cell size, with resulting effects upon their nitrogen uptake, photosynthesis and growth responses to light. We grew two strains of marine centric diatoms differing by ~4 orders of magnitude in cell biovolume in high (enriched artificial seawater with ~500 µmol L^?1 µmol L^?1 NO₃ ^?) and lower-nitrogen (enriched artificial seawater with <10 µmol L^?1 NO₃ ^?) media, across a range of growth light levels. Nitrogen and total protein per cell decreased with increasing growth light in both species when grown under the lower-nitrogen media. Cells growing under lower-nitrogen media increased their cellular allocation to RUBISCO and their rate of electron transport away from PSII, for the smaller diatom under low growth light and for the larger diatom across the range of growth lights. The smaller coastal diatom Thalassiosira pseudonana is able to exploit high nitrogen in growth media by up-regulating growth rate, but the same high-nitrogen growth media inhibits growth of the larger diatom species.     

A low-latitude bloom of the surf-zone diatom, Anaulus australis (Centrales, Bacillariophyta) on the coast of Southern Queensland (Australia)

A novel bloom of the surf diatom Anaulus australis Drebes etSchultz was observed in subtropical waters off Surfers' Paradise,Queensland, Australia (27°55'S; 153°23'E) in early May2000. This is the lowest latitude in which an Anaulus australissurf diatom bloom has been reported. Nitrogen stable isotopeanalysis of surf diatoms may indicate anthropogenic nutrientinputs in this environment.