Design and synthesis of plasmonic magnetic nanoparticles

Core–shell nanoparticles containing both iron oxide and gold are proposed for bioseparation applications. The surface plasmon resonance of gold makes it possible to track the positions of individual particles, even when they are smaller than the optical diffraction limit. The synthesis of water-dispersible iron oxide-gold nanoparticles is described. Absorption spectra show the plasmon peaks for Au shells on silica particles, suggesting that thin shells may be sufficient to impart a strong surface plasmon resonance to iron oxide-gold nanoparticles. Dark field optical microscopy illustrates the feasibility of single-particle detection. Calculations of magnetophoretic and drag forces for particles of different sizes reveal design requirements for effective separation of these small particles.     

Optical properties of plasmonic silver nanoparticles exposed to organic solvents

The influence of ethanol and acetic acid on the structure and optical properties of silver granular films formed by physical vapor deposition in a high vacuum on sapphire substrates was studied via optical spectroscopy and scanning electron microscopy. It was found that irregularly shaped oblate silver grains transforms into almost spherical nanoparticles. Simultaneously, optical extinction spectra shift in the short wavelength range and become narrower. The same effect was observed when liquid crystal was poured on such film. It was noticed, that nanoparticle shapes change under the action of these fluids in the same way as in the process of thermal annealing. This analogy suggests that the observed effects could be explained by acceleration of atomic diffusion over the islet surfaces. It was noticed also that the resistance of thick granular films changes abruptly several minutes after pouring such film with ethanol. This jump of resistance is also very similar to the resistance jump observed previously in the case of annealing.     

Electrochemical method for the synthesis of silver nanoparticles

The article deals with a novel electrochemical method of preparing long-lived silver nanoparticles suspended in aqueous solution as well as silver powders. The method does not involve the use of any chemical stabilising agents. The morphology of the silver nanoparticles obtained was studied using transmission electron microscopy, scanning electron microscopy, atomic force microscopy and dynamic light scattering measurements. Silver nanoparticles suspended in water solution that were produced by the present technique are nearly spherical and their size distribution lies in the range of 2 to 20 nm, the average size being about 7 nm. Silver nanoparticles synthesised by the proposed method were sufficiently stable for more than 7 years even under ambient conditions. Silver crystal growth on the surface of the cathode in the electrochemical process used was shown to result in micron-sized structures consisting of agglomerated silver nanoparticles with the sizes below 40 nm.     

Size-controlled magnetic nanoparticles with lecithin for biomedical applications

Lecithin-adsorbed magnetic nanoparticles were prepared by three-step process that the thermal decomposition was combined with ultrasonication. Experimental parameters were three items—molar ratio between Fe(CO)₅ and oleic acid, keeping time at decomposition temperature and lecithin concentration. As the molar ratio between Fe(CO)₅ and oleic acid, and keeping time at decomposition temperature increased, the particle size increased. However, the change of lecithin concentration did not show the remarkable particle size variation.     

Searching for better plasmonic materials

Plasmonics is a research area merging the fields of optics and nanoelectronics by confining light with relatively large free‐space wavelength to the nanometer scale ‐ thereby enabling a family of novel devices. Current plasmonic devices at telecommunication and optical frequencies face significant challenges due to losses encountered in the constituent plasmonic materials. These large losses seriously limit the practicality of these metals for many novel applications. This paper provides an overview of alternative plasmonic materials along with motivation for each material choice and important aspects of fabrication. A comparative study of various materials including metals, metal alloys and heavily doped semiconductors is presented. The performance of each material is evaluated based on quality factors defined for each class of plasmonic devices. Most importantly, this paper outlines an approach for realizing optimal plasmonic material properties for specific frequencies and applications, thereby providing a reference for those searching for better plasmonic materials.     

Size-controlled synthesis of superparamagnetic iron oxide nanoparticles and their surface coating by gold for biomedical applications

The size mono-dispersity, saturation magnetization, and surface chemistry of magnetic nanoparticles (NPs) are recognized as critical factors for efficient biomedical applications. Here, we performed modified water-in-oil inverse nano-emulsion procedure for preparation of stable colloidal superparamagnetic iron oxide NPs (SPIONs) with high saturation magnetization. To achieve mono-dispersed SPIONs, optimization process was probed on several important factors including molar ratio of iron salts [Fe³⁺ and Fe²⁺], the concentration of ammonium hydroxide as reducing agent, and molar ratio of water to surfactant. The biocompatibility of the obtained NPs, at various concentrations, was evaluated via MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay and the results showed that the NPs were non-toxic at concentrations <0.1 mg/mL. Surface functionalization was performed by conformal coating of the NPs with a thin shell of gold (∼4 nm) through chemical reduction of attached gold salts at the surface of the SPIONs. The Fe₃O₄ core/Au shell particles demonstrate strong plasmon resonance absorption and can be separated from solution using an external magnetic field. Experimental data from both physical and chemical determinations of the changes in particle size, surface plasmon resonance optical band, phase components, core–shell surface composition, and magnetic properties have confirmed the formation of the mono-dispersed core–shell nanostructure.     

Efficiency of protective dermal equipment against silver nanoparticles with water aerosol

Protective dermal equipment (PDE) should be provided for protecting against the penetration of nanomaterials into the skin in the workplace. It is important that workers utilize appropriate PDE with characteristics to accomplish this. During the liquid-phase process, nanomaterials are released with water aerosol, which can easily affect the health of workers. The efficiency of PDE in protecting workers against silver nanoparticles (AgNPs) aerosolized with water aerosol was evaluated. The rate of penetration of AgNPs with water aerosol through cleanroom wear was faster than that for a lab coat. This can be attributed to differences in the filling rate of water, as the result of differences in capillary force. Therefore, humidity appears to be a major factor in the rate of penetration of nanomaterials in the presence of water aerosol. Although no penetration was observed when disposable protective gloves were observed, the presence of AgNPs on the surface of gloves was clearly found. Based on these findings, recommendations for the safe use of PDE can now be made.     

Mg micro/nanoscale materials with sphere-like morphologies: Size-controlled synthesis and characterization

Mg micro/nanoscale materials with sphere-like morphologies are prepared via a vapor-transport deposition process. The structure and morphology of the as-prepared products are characterized by powder X-ray diffraction and scanning electron microscopy. Vapor-liquid-solid mechanism is proposed to explain the formation of Mg micro/nanospheres on the basis of the experimental results. Supported by the National Basic Research Program of China (Grant No. 2005CB623607)     

Photocatalytic synthesis of silver nanoparticles using polysilane initiator

This study shows that the exposure to visible light of the poly[diphenylsilane-co-methyl(H)silane] solution together with a silver salt, initiates a photocatalytic process which leads to the formation of metal nanoparticles. This phenomenon is a consequence of close-range interactions between the methylhydrosilyls’ σ-conjugated segments and the metal ions at the salt surface. Due to the weak charge transfer complexes thin films casted from solution show a specific morphology with microdomains of various dimensions and shapes in relation with the stage of the process. The polymethylhydrosilane copolymer stabilizes the synthesized nanoparticles in a similar manner as the conventional surfactants do. The polymer chemical structure is not affected during the photocatalytic process and the optical and electronic properties of polysilanes are well preserved.     

Green synthesis of silver nanoparticles by Phoma glomerata

We report an extracellular synthesis of silver nanoparticles (SNPs) by Phoma glomerata (MTCC-2210). The fungal filtrate showed rapid synthesis in bright sunlight. The Fourier transform infrared spectroscopy (FTIR) revealed the presence of a protein cap on the silver nanoparticle, which leads to increase stability of SNP in the silver colloid. X-ray diffraction (XRD) analysis showed the number of Bragg's reflection, which are due to the face centered cubic structure of the crystalline SNPs. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoparticle tracking and analysis (NTA) demonstrated the synthesis of polydispersive and spherical SNPs. Energy dispersive X-ray spectroscopy (EDX) was used to confirm the elemental composition of the sample and Zeta potential measurement was carried out to determine the stability of mycofabricated SNPs.The alkaline pH, room temperature, sunlight demonstrated optimum synthesis. Apart from the physical conditions, concentration of silver nitrate and amount of fungal filtrate affects the mycofabrication process. The study of cultural and physical parameters during the mycofabrication of SNPs by P. glomerata will be helpful in order to increase the yield of mycofabricated SNPs of desired shape and size. The process of mycofabrication of SNPs by P. glomerata was found to be eco-friendly, safe and cost-effective nature.     

Size-controlled nanoparticles by thermal cracking of iron pentacarbonyl

A gas-phase method has been developed for producing size-controlled nanoparticles by thermal cracking of iron pentacarbonyl. The method includes the formation of iron particles from vapor emanating from the cracking of the volatile compound and subsequent compacting of the selected particles. Different temperature steps were involved in the process, and their effects on the particle production were investigated. On-line differential mobility measurements and off-line transmission electron microscopy (TEM) were used to study the morphology, composition and structure of the generated particles. The aim of the study was to produce nanoparticles of pure iron. After transportation in air, the composition of the particles was analyzed by TEM and found to be magnetite, Fe₃O₄. The oxidation may be attributed to the exposure to air and humidity during the transport. The phase of the uncontaminated particles could not be determined. Tests for growth of silicon nanowhiskers using nanoparticles produced with this method were successful. PACS 61.46.+w; 81.07.-b; 81.20.Rg     

Hyperthermal chaotic photodesorption of xenon from alumina-supported silver nanoparticles: plasmonic coupling and plasmon-induced desorption

Excitation of Xe monolayers on alumina-supported silver nanoparticles (AgNPs) by laser light in the (1,0) Mie plasmon resonance can lead to desorption of Xe atoms with hyperthermal energy and chaotic time structure. The chaotic behavior is most likely due to plasmonic coupling between AgNPs. We argue that the desorption is induced by direct energy transfer to the adsorbate from the Pauli repulsion of the collectively oscillating electrons of the plasmon at the surface. A simple model calculation shows that this is possible. A connection between both effects appears likely.     

Optical manipulation of plasmonic nanoparticles

We investigate numerically the optical forces exerted by an incident light beam on metal nanoparticles (MNP) sustaining the so-called localized surface plasmons (LSP). We first describe how the particle dispersion can be used to tune the respective contribution from extinction and gradient forces. By a suitable adjustment of the illumination conditions, single MNP can be selectively guided, sorted and trapped. The second part of our work investigates the interparticle forces existing within a MNP ensemble. Our results show that MNP located in a conventional optical trap can self-arrange under optical forces according to specific architectures. In particular, at very low distances, they tend to agglomerate into metal clusters leading to very high field concentration in the interstices. PACS 71.45.Gm; 71.36.+c; 87.80.Cc     

Ion synthesis of silver nanoparticles in viscous-fluid epoxy resin

A method is described for the ion synthesis of silver nanoparticles in epoxy resin that is in a viscousfluid state (viscosity 30 Pa s) during irradiation. The viscous-fluid or glassy polymer is implanted by 30-keV silver ions at a current density of 4 μA/cm² in the ion beam in the dose range 2.2 × 10¹⁶–7.5 × 10¹⁶ ions/cm². The epoxy layers thus synthesized contain silver nanoparticles, which are studied by transmission electron microscopy and optical absorption spectroscopy. The use of the viscous-fluid state increases the diffusion coefficient of the implanted impurity, which stimulates the nucleation and growth of nanoparticles at low implantation doses and allows a high factor of filling of the polymer with the metal to be achieved.     

Controllable synthesis and characterization of highly fluorescent silver nanoparticles

Journal of Nanoparticle Research - Highly fluorescent silver nanoparticles (AgFNPs) have been prepared by microemulsion method and the sizes of AgFNPs were controlled by altering the molar ratio...     

Microbial synthesis of silver nanoparticles by Bacillus sp.

A silver resistant Bacillus sp. was isolated through exposure of an aqueous AgNO₃ solution to the atmosphere. Silver nanoparticles were synthesized using these airborne bacteria (Bacillus sp.). Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analyses confirmed that silver nanoparticles of 5–15 nm in size were deposited in the periplasmic space of the bacterial cells; a preferable cell surface location for the easy recovery of biogenic nanoparticles.     

Facile synthesis of gelatin‐protected silver nanoparticles for SERS applications

Gelatin‐protected silver nanoparticles have been synthesized by a one‐pot, green method for surface‐enhanced Raman scattering (SERS) applications using gelatin as the reducing and stabilizing agent. The gelatin protection on silver nanoparticle surface helps improve its stability greatly and water dispersibility, while retaining high SERS activity of silver nanoparticles. The gelatin‐protected silver nanoparticles showed SERS signals as low as 100 nM of the typical Raman reporter molecules, RuBPY and R6G and 10 μM of other molecules of interest, melamine and folic acid. Copyright © 2013 John Wiley & Sons, Ltd.     

Sectional area-dependent plasmonic shifting in the truncated process of silver nanoparticles: from cube to octahedron

A silver nanocube with sub-40 nm edge length was truncated by {111} planes and transformed into octahedron gradually. The extinction cross-section spectra corresponding to this process were studied by using the discrete dipole approximation (DDA) method. Non-monotonous shifting (blue shifts first and then red shifts) of the surface plasmon resonance (SPR) bands was observed. It was found that the sectional area of {111} facets could be a new and better factor to characterize the shape-dependent non-monotonous shifting of the SPR. The area of {111} facet increases while the SPR peak red shifts, whereas decreases while the SPR peak blue shifts. Similar results were also observed while an octahedron has been truncated into a smaller cube. The physical mechanism was illuminated by analyzing the local field distribution of the nanoparticles with different truncated ratios. The distance of the charge center was one of the most important reasons to affect the shift of SPR as the sectional area of {111} facet is changed. We believe the sectional area factor could be widely used to investigate the SPR shifting in other kinds of truncated process.