Visible‐Light‐Induced Directed Gold Microwires by Self‐Organization of Nanoparticles on Aspergillus Niger

A directional point‐to‐point growth of microwires of gold nanoparticles (AuNPs) self‐organized on Aspergillus niger (A. niger) templates by utilizing positive phototropic fungal response to different spectral ranges of visible light is reported. A. niger serves as a living template for the self‐organization of monosodium glutamate (MSG) capped gold colloids under controlled nutrient trigger and appropriate light, temperature, and humidity conditions. The experimental results show that control of these parameters eliminates the need for any microchannels for the directional growth of microwires. The growth rate of fungal hyphae increases exponentially under light illumination compared to its growth in the dark under similar conditions. White light is found to be most suitable to trigger the directional growth. Gold microwires of about 1 to 2 μm diameter and length exceeding 1 mm are grown within a week with a maximum divergence of 40–50° from the light path regardless of the wavelength of the light irradiation. Phototropic response of fungi has been investigated intensively over the last three decades, but this is the first report on the collective use of microbial tropism and directed biomimetic self‐organization of metallic nanoparticles on living organisms.     

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.     

Toxicity and cellular uptake of gold nanoparticles: what we have learned so far?

Gold nanoparticles have attracted enormous scientific and technological interest due to their ease of synthesis, chemical stability, and unique optical properties. Proof-of-concept studies demonstrate their biomedical applications in chemical sensing, biological imaging, drug delivery, and cancer treatment. Knowledge about their potential toxicity and health impact is essential before these nanomaterials can be used in real clinical settings. Furthermore, the underlying interactions of these nanomaterials with physiological fluids is a key feature of understanding their biological impact, and these interactions can perhaps be exploited to mitigate unwanted toxic effects. In this Perspective we discuss recent results that address the toxicity of gold nanoparticles both in vitro and in vivo, and we provide some experimental recommendations for future research at the interface of nanotechnology and biological systems.     

大尺寸硫醇配体保护金团簇的激发态动力学研究

纳米金团簇作为桥梁连接了金纳米粒子和单个金原子,对于揭示表面等离子激元共振和金属键的来源具有重要意义。有机配体保护的纳米金团簇为理解金纳米粒子从金属性质到非金属性质的转变提供了理想的研究对象,而处于转变区域的金团簇的激发态动力学还尚待研究。在本文中,我们总结了表现出分子性质,并且尺寸较大（大于100 个金原子）的纳米金团簇的激发态动力学,同时将其与表现出金属性质的金纳米粒子的激发态动力学进行比较。本文通过对处于转变区域的金团簇的电子和振动动力学的描述,进一步讨论了其电子结构。对大尺寸纳米金团簇激发态弛豫机理的深入理解,将有助于理解金属纳米团簇和纳米粒子的光学性质,从而进一步推动这一类功能材料的设计和应用。     

Cavity ring-down spectroscopy of metallic gold nanoparticles

The optical properties of supported gold nanoparticles with sizes of 1.3 nm, 1.6 nm, 2.5 nm, and 2.9 nm have been studies by using cavity ring-down spectroscopy in the photon energy range between 1.8 eV and 3.0 eV. The obtained results show the possibility to obtain optical information of nanoassembled materials with high sensitivity. The experimental findings are compared to calculations using Mie-Drude theory. Whereas the broadening of the surface plasmon resonance with decreasing size is well described by this model, the observed blue-shift of the surface plasmon resonance contradicts the predictions of the Mie-Drude theory. The latter effect can be explained by the presence of a skin region with decreased polarizability typical for coinage metal particles. Furthermore, it is found that the supported gold nanoparticles are robust under ambient conditions, an important issue when using these materials for optical applications.     

Seed-mediated shape evolution of gold nanomaterials: from spherical nanoparticles to polycrystalline nanochains and single-crystalline nanowires

We studied the kinetics of the reduction of a gold precursor (HAuCl₄) and the effect of the molar ratio (R) of sodium citrate, which was introduced from a seed solution, and the gold precursor on the shape evolution of gold nanomaterials in the presence of preformed 13 nm gold nanoparticles as seeds. The reduction of the gold precursor by sodium citrate was accelerated due to the presence of gold seeds. Nearly single-crystalline gold nanowires were formed at a very low R value (R = 0.16) in the presence of the seeds as a result of the oriented attachment of the growing gold nanoparticles. At a higher R value (R = 0.33), gold nanochains were formed due to the non-oriented attachment of gold nanoparticles. At a much higher R value (R = 1.32), only larger spherical gold nanoparticles grown from the seeds were found. In the absence of gold seeds, no single-crystalline nanowires were formed at the same R value. Our results indicate that the formation of the 1D nanostructures (nanochains and nanowires) at low R values is due to the attachment of gold nanoparticles along one direction, which is driven by the surface energy reduction, nanoparticle attraction, and dipole–dipole interaction between adjacent nanoparticles.     

Sonosynthesis of gold nanoparticles from a geranium leaf extract

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV–Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8–20 nm, with an average size of 12 ± 3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.     

Synthesis of camptothecin-loaded gold nanomaterials

Camptothecin-loaded gold nanomaterials have been synthesized by the sodium borohydride reduction method under a strong basic condition. The obtained gold nanomaterials have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-vis absorption spectroscopy. The camptothecin-loaded gold colloidal solution was very stable and can be stored for more than two months at room temperature without obvious changes. The color of the colloidal solution can change from wine red to purple and blue during the acidifying process. It was revealed that the release of camptothecin and the aggregation of gold nanoparticles can be controlled by tuning the solution pH. The present study implied that the gold nanomaterials can be used as the potential carrier for CPT delivery.     

Aptamer‐Assisted Assembly of Gold Nanoframe Dimers

The assembly of nanoframe dimers assisted by aptamer‐functionalized smaller spherical gold nanoparticles as prospective surface‐enhanced Raman scattering (SERS) biotraps for riboflavin, an important molecule for biological electron transfer reactions, is reported. In this approach, the aptamer‐coated gold nanoparticles designed for selective binding of riboflavin also serve as the electrostatic driver for nanoframe dimerization in dilute solutions. The gold nanoframe dimers provide unique conditions for plasmonic coupling in a hot spot with sufficient space for the binding of bulky biomolecules. The use of an aptamer allows for highly selective binding of the targeted analyte as compared with conventional organic ligands with excellent low detection limit of one micromole of riboflavin.     

Use of peptide for selective and sensitive detection of an Anthrax biomarker via peptide recognition and surface‐enhanced Raman scattering

A short 16‐amino acid peptide has been used in place of an antibody to selectively detect the specific Anthrax biomarker, protective antigen (PA), using surface‐enhanced Raman scattering (SERS). Peptides are more stable than antibodies under various biological conditions and are easily synthesized for a specific target. A peptide that has high affinity to PA was conjugated onto gold nanoparticles along with a Raman reporter and then incubated in various concentrations of PA. Parallel studies in which the peptide sequence was replaced with an antibody were performed to compare the performance of the two methodologies. Both the peptide and antibody functionalized nanoparticles were able to specifically detect PA concentrations down to 6.1 fM . These results demonstrate that these short, robust peptides can be used in the place of traditional antibodies to specifically recognize target biomarkers in the field for the potential diagnosis of disease. Copyright © 2010 John Wiley & Sons, Ltd.     

A sunlight-induced method for rapid biosynthesis of silver nanoparticles using an <Emphasis Type="Italic">Andrachnea chordifolia</Emphasis> ethanol extract

In this study a sunlight-induced method for rapid synthesis of silver nanoparticles using an ethanol extract of Andrachnea chordifolia is described. The silver nitrate solutions (1 mM) containing the ethanol extract of Andrachnea chordifolia were irradiated by both sunlight radiation and by sunlight radiation passed through different colored filters (red, yellow or green). The smallest size of silver nanoparticles was obtained when a silver ion solution was irradiated for 5 minutes by direct sunlight radiation. Further examination of the shape and size and of the surface chemistry of these biogenic silver nanoparticles, which were prepared under sunlight radiation, was carried out using transmission electron microscopy and infrared spectroscopy, respectively. Transmission electron microscopy images show spherical particles with an average size of 3.4 nm. Hydroxyl residues were also detected on the surface of these biogenic silver nanoparticles fabricated using plant extract of Andrachnea chordifolia under sunlight radiation. Our study on the reduction of silver ions by this plant extract in darkness shows that the synthesis process can take place under dark conditions at much longer incubations (48 hours). Larger silver polydispersed nanoparticles ranging in size from 3 to 30 nm were obtained when the silver ions were treated with the ethanol extract of Andrachnea chordifolia under dark conditions for 48 hours.     

Silver nanoparticles in simulated biological media: a study of aggregation,sedimentation, and dissolution

Nanoparticles, the building blocks of many engineered nanomaterials, can make their way into the environment or into organisms, either accidentally or purposefully. The intent of this study is to provide some insight into the complex environmental, health, and safety issues associated with engineered nanomaterials. In particular, here the state of commercially manufactured silver nanoparticles—i.e., will silver nanoparticles be present as isolated particles, agglomerates, or dissolved ions—in two simulated biological media is explored. Two different commercially manufactured silver nanoparticle samples, one that has been surface modified with a thick polymer coating to render them more water-soluble and the other, with a sub-nanometer surface layer, are studied. The experimental results and the extended DLVO model calculations show that silver nanoparticles have a propensity to settle out in high ionic strength media independent of surface modification. Furthermore, single nanoparticles as well as aggregates/agglomerates are present together in these solutions. Silver ion release in these simulated biological buffers with pHs of 4.5 and 7.4 is negligible after 96 h.     

Extracellular biosynthesis of monodispersed gold nanoparticles by a SAM capping route

Monodispersed gold nanoparticles capped with a self-assembled monolayer of dodecanethiol were biosynthesized extracellularly by an efficient, simple, and environmental friendly procedure, which involved the use of Bacillus megatherium D01 as the reducing agent and the use of dodecanethiol as the capping ligand at 26 °C. The kinetics of gold nanoparticle formation was followed by transmission electron microscope (TEM) and UV-vis spectroscopy. It was shown that reaction time was an important parameter in controlling the morphology of gold nanoparticles. The effect of thiol on the shape, size, and dispersity of gold nanoparticles was also studied. The results showed that the presence of thiol during the biosynthesis could induce the formation of small size gold nanoparticles (<2.5 nm), hold the shape of spherical nanoparticles, and promote the monodispersity of nanoparticles. Through the modulation of reaction time and the use of thiol, monodispersed spherical gold nanoparticles capped with thiol of 1.9 ± 0.8 nm size were formed by using Bacillus megatherium D01.     

Tunable gold nanoparticles shape and size in reductive and structuring media containing protic ionic liquids

Herein, a facile method was developed for preparing high concentration of monodispersed gold nanoparticles (NPs) at room temperature from gold(III) chloride by using different media based on N,N-dimethylformamide or water solutions containing a protic ionic liquid (PIL), namely, the octylammonium formate or the bis(2-ethyl-hexyl)ammonium formate, based on which both PILs were used as redox-active structuring media. The formation of gold NPs in these systems was then characterized using UV–visible spectroscopy, transmission electron microscopy, and dynamic light scattering. From these investigations, it appears that the structure and aggregation pathway of PILs in selected solvents affect strongly the formation, growth, the shape, and the size of gold NPs. In fact, by using this approach, the shape-/ size-controlled gold NPs (branched and spherical) can be generated under mild condition. This approach suggests also a wealth of potential for these designer nanomaterials within the biomedical, materials, and catalysis communities by using designer and safer media based on PILs.     

Protein-assisted synthesis route of metal nanoparticles: exploration of key chemistry of the biomolecule

Abstract  

Essentially, biomolecule assisted synthesis of inorganic nanoparticles can be divided into two categories. One uses multi-domain protein cages (template) and other relies on the self-assembly of the biomolecules including small peptides, DNA, and denatured protein. Protein templated synthesis of various nanomaterials is relatively well understood as the cages of the biological macromolecules and their specific interaction with inorganic ions ultimately dictate the size and crystallinity of the nanomaterials. On the other hand formation of nanoparticles using protein in the cost of the native structural integrity for the self-assembly is not well understood till date. In the present work we report a protein-assisted synthesis route to prepare highly crystalline 3–5 nm gold nanoparticles, which relies systematic thermal denaturation of a number of proteins and protein mixture from Escherichia coli in absence of any reducing agent. By using UV–vis, circular dichroism spectroscopy, and high-resolution transmission electron microscopy we have explored details of the associated biochemistry of the proteins dictating kinetics, size, and crystallinity of the nanoparticles. The kinetics of nanoparticles formation in this route, which is sigmoidal in nature, has been modelled in a simple scheme of autocatalytic process. Interestingly, the protein-capped as prepared Au nanoparticles are found to serve as effective catalyst to activate the reduction of 4-nitrophenol in the presence of NaBH₄. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy revealing the efficient catalytic activity of the nanoparticles have been explained in terms of the Langmuir–Hinshelwood model. The methodology and the details of the protein chemistry presented here may find relevance in the protein-assisted synthesis of inorganic nanostructures in general.     

How can nanobiotechnology oversight advance science and industry: examples from environmental,health, and safety studies of nanoparticles (nano-EHS)

Nanotechnology has great potential to transform science and industry in the fields of energy, material, environment, and medicine. At the same time, more concerns are being raised about the occupational health and safety of nanomaterials in the workplace and the implications of nanotechnology on the environment and living systems. Studies on environmental, health, and safety (EHS) issues of nanomaterials have a strong influence on public acceptance of nanotechnology and, eventually, affect its sustainability. Oversight and regulation by government agencies and non-governmental organizations (NGOs) play significant roles in ensuring responsible and environmentally friendly development of nanotechnology. The EHS studies of nanomaterials can provide data and information to help the development of regulations and guidelines. We present research results on three aspects of EHS studies: physico-chemical characterization and measurement of nanomaterials; emission, exposure, and toxicity of nanomaterials; and control and abatement of nanomaterial releases using filtration technology. Measurement of nanoparticle agglomerates using a newly developed instrument, the Universal NanoParticle Analyzer (UNPA), is discussed. Exposure measurement results for silicon nanoparticles in a pilot scale production plant are presented, as well as exposure measurement and toxicity study of carbon nanotubes (CNTs). Filtration studies of nanoparticle agglomerates are also presented as an example of emission control methods.     

Effects of electrolytes on the fabrication of three‐dimensional nanoporous gold films by a rapid anodic potential step method for SERS

A unique one‐step anodic potential step strategy has been developed recently by our group to fabricate a three‐dimensional (3D) nanoporous gold film (NPGF) within 1 min as an efficient surface‐enhanced Raman scattering (SERS) active substrate. Gloria et al. (J. Electroanal. Chem. 2011, 656, 114–119) demonstrated that the prepared NPGF under optimum conditions (2 M HCl, 50 s) has higher SERS intensities than that of a commercial single‐use gold substrate. However, the SERS performance of 3D NPGFs fabricated in neutral KCl by this strategy have not been investigated. In this paper, SERS performances of the NPGFs fabricated in electrolytes of KCl and HCl are compared for the first time, using pyridine as a test molecule. Equivalent SERS intensities can be obtained on the 3D NPGFs prepared in these two electrolytes under respectively optimum conditions. The results suggest that hot spots of nanogaps and crevices because of the aggregation/coalescence of gold nanoparticles and the formation/removal of thin gold oxide coatings contribute greatly to the high SERS activity. Copyright © 2012 John Wiley & Sons, Ltd.     

High-intensity near-field generation for silicon nanoparticle arrays with oblique irradiation for large-area high-throughput nanopatterning

We present near-field distributions around an isolated 800-nm silica or silicon nanoparticle, and nanoparticle arrays of 800-nm silica or silicon nanoparticles, on a silicon substrate by the finite-difference time-domain method when 800-nm light is irradiated obliquely to the substrate. Nanopatterning mediated with the nanoparticle system is promising for large-area, high-throughput patterning by using an enhanced localized near-field ablation by the nanoscattered light lens effect. The irradiation area cannot be extended for silica nanoparticles, because the optical field enhancement factor is low. Gold nanoparticles can generate highly enhanced near fields, although at present there are no useful ways to arrange the gold nanoparticles on the substrate at a high throughput. Silicon nanoparticles with high dielectric permittivity have optical characteristics of both silica and gold nanoparticles. The particle arrangement on the Si substrate is technically easy using a wet pulling process. From the calculation, high optical field intensity is acquired with oblique s-polarized irradiation to the substrate under silicon nanoparticle arrays, and the intensity is almost the same as that under gold nanoparticle arrays under the same condition. With this method, high-throughput nanopatterning for a large area would be achievable.     

<Superscript>56</Superscript>Co-labelled radioactive Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for in vitro uptake studies on Balb/3T3 and Caco-2 cell lines

Magnetite nanoparticles (Fe₃O₄ NPs) are manufactured nanomaterials increasingly used in healthcare for different medical applications ranging from diagnosis to therapy. This study deals with the irradiation of Fe₃O₄ NPs with a proton beam in order to produce ⁵⁶Co as radiolabel and also with the possible use of nuclear techniques for the quantification of Fe₃O₄ NPs in biological systems. Particular attention has been focused on the size distribution (in the range of 100 nm) and the surface charge of the NPs characterizing them before and after the irradiation process in order to verify if these essential properties would be preserved during irradiation. Moreover, X-ray diffraction studies have been performed on radioactive and non-radioactive NPs, to assess if major changes in NPs structure might occur due to thermal and/or radiation effects. The radiation emitted from the radiolabels has been used to quantify the cellular uptake of the NPs in in vitro studies. As for the biological applications two cell lines have been selected: immortalized mouse fibroblast cell line (Balb/3T3) and human epithelial colorectal adenocarcinoma cell line (Caco-2). The cell uptake has been quantified by radioactivity measurements of the ⁵⁶Co radioisotope performed with high resolution γ-ray spectrometry equipment. This study has showed that, under well-established irradiation conditions, Fe₃O₄ NPs do not undergo significant structural modifications and thus the obtained results are in line with the uptake studies carried out with the same non-radioactive nanomaterials (NMs). Therefore, the radiolabelling method can be fruitfully applied to uptake studies because of the low-level exposure where higher sensitivity is required.     

Influence of the deposition parameters on the properties of SnS2 films prepared by PECVD method combined with solid sources

We report a simple and rapid biological approach to synthesize water-soluble and highly roughened “meatball”-like Au nanoparticles using green tea extract under microwave irradiation. The synthesized Au meatball-like nanoparticles possess excellent monodispersity and uniform size (250 nm in diameter). Raman measurements show that these tea-generated meatball-like gold nanostructures with high active surface areas exhibit a high enhancement of surface-enhanced Raman scattering. In addition, the Au meatball-like nanoparticles demonstrate good biocompatibility and remarkable in vitro stability at the biological temperature. Meanwhile, the factors that influence the Au meatball-like nanoparticles morphology are investigated, and the mechanisms behind the nonspherical shape evolution are discussed.