Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support^1,2,3. In this context, metal nanowires are especially desirable for realizing dense routing networks⁴. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons⁵ in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires⁶ randomly distributed on a glass substrate⁷. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization^8,9. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity^5,9. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate^9,10. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy^9,11. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry.     

Negative Refraction and Focusing Properties of Silver Nanowires Array with Different Cross-Sections

A three-dimensional silver metallic nanowires array which can realize negative refraction and image focusing in the visible frequency is presented. Homogeneous effective medium theory is used to investigate the negative refraction properties when the cell size of the array is much smaller than the incident wavelength. The analytical results are confirmed by Finite Difference Time Domain (FDTD) numerical simulations. The imaging properties comparison among the nanowires arrays with triangle, circle, ellipse, hexagon, and square wire cross-sections which have the same filling factor show the structure shapes of the nanowires will not influence the negative refraction but the imaging properties because of the different loss from the metal nanowires.     

Promoting Cell Proliferation Using Water Dispersible Germanium Nanowires

Group IV Nanowires have strong potential for several biomedical applications. However, to date their use remains limited because many are synthesised using heavy metal seeds and functionalised using organic ligands to make the materials water dispersible. This can result in unpredicted toxic side effects for mammalian cells cultured on the wires. Here, we describe an approach to make seedless and ligand free Germanium nanowires water dispersible using glutamic acid, a natural occurring amino acid that alleviates the environmental and health hazards associated with traditional functionalisation materials. We analysed the treated material extensively using Transmission electron microscopy (TEM), High resolution-TEM, and scanning electron microscope (SEM). Using a series of state of the art biochemical and morphological assays, together with a series of complimentary and synergistic cellular and molecular approaches, we show that the water dispersible germanium nanowires are non-toxic and are biocompatible. We monitored the behaviour of the cells growing on the treated germanium nanowires using a real time impedance based platform (xCELLigence) which revealed that the treated germanium nanowires promote cell adhesion and cell proliferation which we believe is as a result of the presence of an etched surface giving rise to a collagen like structure and an oxide layer. Furthermore this study is the first to evaluate the associated effect of Germanium nanowires on mammalian cells. Our studies highlight the potential use of water dispersible Germanium Nanowires in biological platforms that encourage anchorage-dependent cell growth.     

Near-Infrared Fluorescence Enhancement Using Silver Island Films

Near-infrared (near-IR) excitation produces little background signal from biological molecules, making near-IR fluorescence technology highly useful in proteomic and genomic applications. To increase the emissions of near-IR fluorophores, we examined the use of metal-enhanced fluorescence on these longer wavelength dyes. IRDye^®700- and IRDye^®800-labeled DNA oligonucleotides and proteins were spotted onto silver island film (SIF)-coated glass slides, and analyzed using a LI-COR Odyssey^® IR imaging system. We observed more than 18-fold enhancement of the IRDye^®700 and 15-fold enhancement of the IRDye^®800-labeled DNA oligonucleotides when spotted on SIF-coated surfaces compared with uncoated surfaces. We also demonstrated that the enhanced emissions produced on the SIF-coated slides remained linear over several orders of magnitude, that the emissions remained reproducible across a slide surface, and that the SIF-coated slide remained effective at enhancing emissions after 9 months of storage. Our results indicate that SIF-coated glass slides are effective at enhancing near-IR fluorescence and could be developed into an effective tool to aid in molecular biological applications.     

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures¹. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.     

Effect of Periodicity in the Resonant Scattering of Light by Finite Sparse Configurations of Many Silver Nanowires

We consider the two-dimensional (2-D) scattering of the H- and E-polarized plane waves by several discrete configurations made of M>?>?1 periodically arranged circular cylindrical silver wires. To find the scattered field, we use the field Fourier expansions in local coordinates and addition theorems for cylindrical functions. Resulting M?×?M block-type matrix equation is cast to the Fredholm second-kind form that guarantees convergence of numerical solution when each block is truncated to finite dimensions and truncation order is taken larger. The scattering and absorption cross-sections and the near-field patterns are computed. The interplay of plasmon and grating-type resonances is studied for finite in-line and stacked arrays, corners, and crosses made of nano-size silver wires in the visible range of wavelengths, with the refractive index of silver taken from the experimental data.     

Achieving Invisibility of Homogeneous Cylindrically Anisotropic Cylinders

In this paper, we establish the full-wave electromagnetic scattering theory to study the electromagnetic scattering from infinitely long cylinders with cylindrically anisotropic coatings. We show that the total effective scattering width can be dramatically reduced by the suitable adjustment of the dielectric anisotropy of the shell, while it is not the case for tuning the dielectric anisotropy of the core. Furthermore, we could make the cylindrical objects invisible when both dielectric and magnetic anisotropies are adjusted. In the long wavelength limit, we develop effective medium theory to derive the effective isotropic permittivity and permeability for the anisotropic coated cylinders, and the invisibility radius ratio derived from the full-wave theory for small coated cylinders can be well described within the effective medium theory.     

Cloak and dagger in the avoidance of immune surveillance

CD95 and CD95-ligand (CD95L) are physiological mediators of apoptosis required for the control of cell numbers in the human immune system. Discoveries in CD95-dependent mechanisms of immune evasion by tumours suggest regulation by oncogene expression. Clonal contraction of lymphocytes by a CD95/CD95L-independent mechanism has been reported and new evidence supports a role for CD95-dependent peripheral lymphocyte deletion by non-lymphoid tissue. Additionally, factors affecting the pro- and anti-inflammatory effects of CD95L point to a balance of cytokines and growth factors.     

一种新的DNA银染方法

本文介绍一种有效的聚丙烯酰胺中的DNA银染方法,其具有背景浅、快速、灵敏度高等特点。利用该方法对MarkerX和棉花的RAPD产物进行银染,取得了较满意的结果。说明该方法适于聚丙烯酰胺中的DNA银染。 Abstract：An effective silver staining protocol for DNA in PAGE was introduced in this article,it characterized weak background,sensitivity,time saving .Based on this protocol,MarkerX and products of RAPD were stained,the satisfactory staining map indicated that this silver staining protocol was applicable to DNA in PAGE.     

Near-Infrared,Surface-Enhanced Fluorescence Using Silver Nanoparticle Aggregates in Solution

Fluorescence spectroscopy is used in many life science and clinical research diagnostic assays. Improvements in the sensitivity and limit-of-detection of these assays may have profound implications. Here, we demonstrate a near-infrared, surface-enhanced fluorescence technology that increases the signal of IRDye 800CW-labeled streptavidin by up to 2,530-fold while improving the limit-of-detection 1,000-fold. Citrate-stabilized, silver nanoparticles that aggregate in solution were used with the dye-protein conjugate to form plasmon-active nanostructures. The technique is straightforward to implement and fully compatible with commercially available immunoassay instrumentation and consumables.     

An Improved Silver Stain for Developing Nervous Tissue

A reduced silver technique using physical development to stain embryonic nervous tissue is described. Brains are fixed in Bodian's fixative. Paraffin sections are pretreated with 1% chromic acid or 5% formol. They are impregnated with 0.01% silver nitrate dissolved in 0.1 M boric acid/sodium tetraborate buffer of pH 8 or with silver proteinate. Finally they are developed in a special physical developer which contains 0.1% silver nitrate, 0.01-0.l% formol as developed agent, 25% sodium carbonate to buffer the solution at pH 10.3, 0.1% ammonium nitrate to prevent precipitation of silver hydroxide, and 5% tungstosilicic acid as a protective colloid. The development takes several minutes in this solution, thus the intensity of staining can be controlled easily. The method yields uniform, complete and reproducible staining of axons at all developmental stages of the nervous tissue and is easy to handle.     

Enhanced and Selective Photodetection Using Graphene-Stabilized Hybrid Plasmonic Silver Nanoparticles

We report the fabrication and characteristics of a novel graphene-Ag⁰ hybrid plasmonic nanostructure-based photodetector exhibiting moderately high responsivity (～28 mA/W) and spectral selectivity (～510 nm) in the visible wavelength. The formation of highly stable Ag⁰ nanoparticles with an average size of 40 nm is observed within the graphene layers, resulting in n-type doping of hybrid material. The absorption peak of graphene-Ag⁰ hybrid is redshifted to the visible wavelength (～510 nm) from the plasmonic Ag peak (～380 nm) in agreement with the optical simulation results for embedded metal nanoparticles. The study demonstrates the synergistic effect of the graphene-metal nanocomposite, which appears attractive for applications in graphene-based photonic devices.     

Remote-Excitation Time-Dependent Surface Catalysis Reaction Using Plasmonic Waveguide on Sites of Single-Crystalline Crossed Nanowires

The remote-excitation polarization-dependent surface enhanced Raman scattering (SERS) induced by plasmonic waveguide is used to investigate the surface catalysis reaction of 4-nitrobenzenethiol converting to p,p′-dimercaptoazobenzene. The propagating surface plasmon polaritons along single-crystalline nanowires can be coupled by the crossed nanowire as nanoantenna for generating massive electromagnetic field enhancement in the nanogap. The remote-excitation SERS spectra in the nanogap reveal the occurrence of a surface catalysis reaction. The time-dependent remote-excitation SERS spectra further confirmed such surface catalysis reaction. This novel sensitive technology could lead to miniaturized photonics and realize high-resolution microscopy/spectroscopy used in the field of remote catalysis reaction.     

Multishelled Gold Nanowires

Abstract

The current miniaturization of electronic devices raises many questions about the properties of various materials at nanometre-scales. Recent molecular dynamics computer simulations have shown that small finite nanowires of gold exist as multishelled structures of lasting stability. These classical simulations are based on a well-tested embedded atom potential. Molecular dynamics simulation studies of metallic nanowires should help in developing methods for their fabrication, such as electron-beam litography and scanning tunneling microscopy.     

Enhancement of Dynamic Sensitivity of Multiple Surface-plasmonic-polaritonic Sensor Using Silver Nanoparticles

Multiple surface plasmon-polariton (SPP) waves excited at the interface of a homogeneous isotropic metal and a chiral sculptured thin film (STF) impregnated with silver nanoparticles were theoretically assessed for the multiple-SPP-waves-based sensing of a fluid uniformly infiltrating the chiral STF. The Bruggemann homogenization formalism was used in two different modalities to determine the three principal relative permittivity scalars of the silver-nanoparticle-impregnated chiral STF infiltrated uniformly by the fluid. The dynamic sensitivity increased when silver nanoparticles were present, provided their volume fraction did not exceed about 1 %.     

SERS Study of Histamine by Using Silver Film over Nanosphere Structure

Optical properties of histamine and l-histidine have been analyzed by using surface-enhanced Raman scattering (SERS). A silver film over nanosphere (AgFON) structure with 120-nm-thick silver film on polystyrene nanospheres 1,000?nm in diameter is fabricated by nanosphere lithography to enhance the Raman signal excited at the laser wavelength of 532?nm. Normal Raman spectrum and the SERS spectrum of histamine and l-histidine were compared. Further, vibration modes of these molecules were calculated by using density functional method. In the SERS experiment, we were able to measure the Raman spectrum with a histamine concentration as less as 100?pM. This sensitivity is higher than that from high-performance liquid chromatography.     

The Invisibility of Disability: Using Dance to Shake from Bioethics the Idea of ‘Broken Bodies’

Complex social and ethical problems are often most effectively solved by engaging them at the messy and uncomfortable intersections of disciplines and practices, a notion that grounds the InVisible Difference project, which seeks to extend thinking and alter practice around the making, status, ownership, and value of work by contemporary dance choreographers by examining choreographic work through the lenses of law, bioethics, dance scholarship, and the practice of dance by differently‐abled dancers. This article offers a critical thesis on how bioethics has come to occupy a marginal and marginalizing role in questions about the differently‐abled body. In doing so, it has rendered the disabled community largely invisible to and in bioethics. It then defends the claim that bioethics – as a social undertaking pursued collaboratively by individuals from different disciplines – must take much better notice of the body and the embodied individual if it is to better achieve its ends, which include constructing a moral and just society. Finally, this article considers how the arts, and specifically dance (and here dance by differently‐abled dancers), provides us with rich evidence about the body and our ability to respond positively to normally ‘othered’ bodies. It concludes that greater attention to empirical evidence like that being generated in InVisible Difference will help to expand the reach and significance of bioethics, and thereby its relevance to (and consciousness of) important questions about the status of bodies and bodily differences, which must be considered as central to its ambitions.