Room temperature self-organized gold nanoparticles materials for embedded electronic devices

In this study, we synthesize two different sizes of gold nanoparticles (NPs) with uniform size distribution. A novel technique of fabricating gold NPs embedded capacitor devices utilizing chemical self-assembled gold NPs has been developed. Room temperature process and uniform size distribution of gold NPs device are built and characterized. These electronic devices have lower leakage current, no metal diffusion problem, larger memory window, better charge retention time and following Fowler–Nordheim tunneling model. This method enables the possibility of future memory applications to fabricate devices with this simple and versatile technique based on the NPs assembly.     

Layered polymer-kaolinite nanocomposites

Kaolinite (K) was reacted with liquid dimethyl sulfoxide (DMSO) producing K(DMSO)_0.4. Highly ordered polymer/kaolinite materials were obtained by displacement of DMSO molecules in the K(DMSO)_0.4 intercalate by polyethylene oxide (PEO) or bacterial polyhydroxybutyrate (PHB), both in the melt state at 130°C and 180°C, respectively. The hybrid nanocomposites obtained were characterized by powder X-ray diffractometry (PXRD), Fourier Transform Infrared spectrometry (FTIR) and thermal analysis (simultaneous TG/DSC). The obtained results are consistent with the total replacement of DMSO molecules by the macromolecular linear chains that lie flat building a monolayer of the polymer in the interlayer space of kaolinite. The stoichiometry of the compounds estimated from the TG/DSC measurements are: K(DMSO)_0.40±0.02, K(PHB)_0.82±0.02, K(PEO)_3.40±0.02.     

Paper-based tuberculosis diagnostic devices with colorimetric gold nanoparticles

Abstract

A colorimetric sensing strategy employing gold nanoparticles and a paper assay platform has been developed for tuberculosis diagnosis. Unmodified gold nanoparticles and single-stranded detection oligonucleotides are used to achieve rapid diagnosis without complicated and time-consuming thiolated or other surface-modified probe preparation processes. To eliminate the use of sophisticated equipment for data analysis, the color variance for multiple detection results was simultaneously collected and concentrated on cellulose paper with the data readout transmitted for cloud computing via a smartphone. The results show that the 2.6 nM tuberculosis mycobacterium target sequences extracted from patients can easily be detected, and the turnaround time after the human DNA is extracted from clinical samples was approximately 1 h.     

Third-harmonic generation from single gold nanoparticles

We report the first observation of third-harmonic signals from individual gold colloids down to 40 nm diameter. Excited with 1-ps pulses at 1500 nm, the colloids generate 500-nm light, close to the plasmon resonance. The third-harmonic intensity varies as the square of the colloid surface area. Although weak, the third-harmonic signals of gold labels as small as 15 nm in diameter are expected to be accessible with 100-fs pulses. They could be used in microscopy for single-biomolecule tracking.     

Inverse design techniques for improving composite prosthetic devices

The design and performance of composite prosthetic devices can be improved by tailoring the material properties to achieve a prescribed response. An example of such a response would be displacements and stresses exhibited by healthy, undisturbed femoral bone. In this paper, an inverse design methodology, used in the Volumetrically Controlled Manufacturing (VCM) process, is developed and tested for improving the design of orthopedic prosthetic devices. First, a three-dimensional finite element (FE) model is developed based on available Computed Tomography (CT) data. The FE model is used to evaluate the response of the model subjected to a typical load. Second, as a part of the VCM process, the inverse design process is used to formulate a design problem that is in the form of a constrained least-squares problem. The intent is to find the material properties of the FE model to obtain a known displacement field on the stem-cancellous interface. Third, a solution methodology is developed to solve this constrained least squares problem using the finite element analysis for function evaluations and a gradient-based nonlinear programming (NLP) method to solve the design problem. Two test problems are solved to illustrate the developed methodology. The results indicate that material properties can be tailored to meet specific response requirements.     

Highly efficient multiphoton-absorption-induced luminescence from gold nanoparticles

We demonstrate that highly efficient photoluminescence is generated from gold nanoparticles as small as a few nanometers in diameter upon irradiation with sub-100-fs pulses of 790-nm light. Strong emission is observed at excitation intensities comparable to or less than those typically used for multiphoton imaging of fluorescently labeled biological samples. The particles have polarized emission, can radiate more efficiently than single molecules, do not exhibit significant blinking, and are photostable under hours of continuous excitation. These observations suggest that metal nanoparticles are a viable alternative to fluorophores or semiconductor nanoparticles for biological labeling and imaging.     

Thermoplastic polymer nanocomposites for applications in optical devices

Polymer optical fibres (POF) have superior properties compared to glass fibres like e.g. high flexural strength, uncomplicated mechanical machining and inexpensive mass production. Dispersion of nanoscaled ceramic fillers in polymers allows the modification of the refractive index depending on the ceramic used and the aspired application. Current work deals with the development of a process chain to tailor the refractive index of PMMA using a UV-curable reactive resin and ceramic nanopowders as well as with the ageing behaviour of polymer nanocomposites. Improved dispersion techniques applying high shear forces to deagglomerate the ceramic powders lead to a refractive index shift depending on the ceramic fillers maintaining a transparency of resulting polymer nanocomposites sufficient for optical applications in the visible (633 nm) and in the infrared (1550 nm) regime. Optical devices were obtained using reaction moulding of the modified polymer nanocomposites as rapid prototyping method.     

Glass-ceramic-metal composites for making graded seals in prosthetic devices

The possibility of using glass-ceramic-metal composites as graded seals between dense cores of prostheses and a porous glass-ceramic coating, which would promote a direct bond with the bone has been investigated, particularly with respect to thermal and elastic properties. Before binding them to a core, bulk composite materials have been prepared in order to study their properties.These materials have been obtained from powdered mixtures of a calcium alumino-phosphate glass (CAP) with increasing volume fractions (3.5–50%) of various metals or alloys: titanium, 316 L stainless steel, cobalt-chromium 788 alloy. They have been synthesized by hot pressing immediately followed by a heat treatment to obtain ceramicization of the glass matrix.Elastic and thermal properties have been determined. The values of elastic moduli and average linear thermal expansion coefficients lie within those of glass-ceramic CAP and those of the corresponding metal. Mechanical properties have been also measured. The material can withstand about four times the body weight when materials are bound to a more rigid metal or alloy.     

Characterization and temperature-dependent conductivity of polyaniline nanocomposites encapsulating gold nanoparticles on the surface of carboxymethyl cellulose

Polyaniline nanocomposites encapsulating gold nanoparticles on carboxymethyl cellulose surface were prepared via the polymerization of aniline hydrochloride with different carboxymethyl cellulose (CMC) concentrations (wt.%) using HAuCl₄ as oxidant. The synthesized composites were characterized by Fourier transform infrared (FTIR) spectroscopy. Surface morphology was studied by electron diffraction scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The embedded crystallinity of the composites was investigated by X-ray diffraction (XRD) analyses. The electrical property of the composites was examined by temperature-dependent DC conductivity in the range of 300–500 K. The composites exhibited higher electrical conductivities with increased CMC concentration under equivalent conditions. Activation energy for electron transport was also calculated based on the conductivity data.     

New PMMA-based composites for preparing spacer devices in prosthetic infections

Even though the systemic antibiotic therapy is usually applied after prosthetic infections surgical treatments, it is unable to reach the infection site in sufficient concentrations to eradicate bacteria. Delivering antibiotics locally with the use of custom made device (spacer or nail coating) might eradicate or reduce the infection and the risk of recolonization, providing a very high concentration of antibiotic. PMMA-based (Mendec Spine^®) composites with BaSO₄ were enriched with β-tricalcium phosphate (Porosectan-TCP) or only a slightly higher BaSO₄ concentration (Porosectan-BaSO₄) to obtain higher porosity. The aim of the study was to evaluate: (i) drug absorption capability and drug release kinetics in vitro soaking them with a combined solution of gentamicin and vancomycin, (ii) their in vitro and in vivo biocompatibility, and finally, (iii) they were tested preliminarily in an experimental model of bone infection. The simultaneous presence of β-TCP and BaSO₄ resulted in the formation of a texture of interconnecting channels with different diameters, from a few microns to several hundred microns, which totally filled the material. The porosity, determined by microcomputed tomography, was significantly higher in both tested plain composites (Porosectan-TCP: +17.3%; Porosectan-BaSO₄: +7.5%) in comparison to control composite material (Mendec Spine^®). The kinetics of antibiotic release from composites was rapid and complete, producing high drug concentrations for a short period of time. Both composites showed a good level of biocompatibility. The osteomyelitic model confirmed that both composites, soaked in antibiotic solution, were able to cure bone infection. These composites could be useful for preparing devices for prosthetic joint infections treatment also allowing the use of antibiotics solution at required concentrations.     

Fluorescence near gold nanoparticles for DNA sensing

We investigated fluorescence quenching and enhancement near gold nanoparticles (GNP) of various sizes using fluorescently labeled hairpin DNA probes of different lengths. A closed hairpin caused intimate contact between the fluorophore and the gold, resulting in an efficient energy transfer (quenching). Upon hybridization with complementary DNA, the DNA probes were stretched yielding a strong increase in fluorescence signal. By carefully quantifying the amount of bound fluorescent probes and the GNP concentrations, we were able to determine the quenching and enhancement efficiencies. We also studied the size and distance dependence theoretically, using both FDTD simulations and the Gersten-Nitzan model and obtained a good agreement between experiments and theory. On the basis of experimental and theoretical studies, we report over 96.8% quenching efficiency for all particle sizes tested and a maximal signal increase of 1.23 after DNA hybridization. The described results also demonstrate the potential of gold nanoparticles for label free DNA sensing.     

Paramagnetic silica-coated gold nanoparticles

Water soluble gold nanoparticles, obtained by the reduction of the gold (III) chloride with sodium borohydride in the presence of citric acid or thioctic acid, were covered with a paramagnetic silica layer using the Stober method, yielding a hybrid metallic-inorganic nanomaterial (gold nanoparticles, with an average size of 5 nm, embedded into silica nanoparticles, with an average size of 100 nm). The paramagnetic silica layer was formed by copolymerization of a paramagnetic silica precursor (derived from 3-aminopropyltrimethoxysilane) with tetramethyorthosilicate. The paramagnetic silica precursor was obtained by coupling 3-aminopropyltrimethoxysilane with 3-carboxy-proxyl free radical. TEM pictures show that each silica nanoparticle of about 100 nm in size embedded about 10 gold nanoparticles. These hybrid nanoparticles are quite stable and exhibit the expected paramagnetic characteristics, as seen by electron paramagnetic resonance. The accessibility of methanol through the silica layer was also studied. Depending on the capping ligands of the gold nanoparticles (citric or thioctic acid), different silica networks are formed, as seen by the mobility of the spin-label inside the silica layer. The EPR spectra showed that the paramagnetic silica layer is very robust and the mobility of the spin-probe inside the silica layer is very little affected by methanol. However, if spin-labeled thioctic acid protected gold nanoparticles were used in the material synthesis, the mobility of the spins attached to the gold surface is quite high in the presence of methanol, while the spins embedded into the silica layer remains immobilized.     

Biosynthesis of gold nanoparticles

Synthesis of nanoparticles with interesting physico-chemical properties using efficient as well as eco-friendly technology is one of the main objectives of nanotechnology. Biological systems have been reported to synthesize inorganic materials under certain circumstances. Exploiting the biosynthetic potential of different organisms, nanoparticles of varying morphologies and sizes have been synthesized. Among the nanomaterials, gold has received considerable attention owing to its varied applications in the fields of nano-medicine, catalysis, electronics, and optics. This review gives an account on the biosynthesis of gold nanoparticles from microorganisms, plants, and other biological sources, with particular emphasis on the probable mechanisms leading to the formation of gold nanoparticles and the extent of control over nanoparticle properties that has been achieved so far in the biosynthetic protocols. It has been speculated that enzymes and/or proteins secreted by the organisms are involved in the bio-reduction and stabilization of the nanoparticles. The biosynthetic procedures could compete with existing solvent-based chemical synthetic procedures in order to achieve stable and monodisperse gold nanoparticles in large scale.     

Synthesis of magnetic nanocomposites and alloys from platinum-iron oxide core-shell nanoparticles

This paper presents a systematic study on the generation of iron platinum-containing magnetic nanocomposites and alloys from Pt@Fe(2)O(3) core-shell nanoparticle precursors. These core-shell nanoparticles were made using a sequential synthetic approach. They could form FePt alloys and alloy-containing nanocomposites through a solid-state reaction at >400?°C. The chemical compositions of FePt alloys were controllable by using Pt@Fe(2)O(3) core-shell nanoparticles that had the designed Pt core diameter and iron oxide shell thickness. We show that face-centred tetragonal (fct) FePt@Fe core-shell nanoparticles could be made from Pt@Fe(2)O(3) core-shell nanoparticles with?5% hydrogen in argon (v/v). Furthermore, various FePt alloys and alloy-containing nanocomposites including metastable intermediate phases could be obtained. The materials were characterized by high resolution scanning transmission electron microscopy (HR-STEM), energy dispersive x-ray (EDX) spectroscopy, powder x-ray diffraction (PXRD), parallel electron energy loss spectroscopy (PEELS), and superconducting quantum interference device (SQUID) magnetometry. These materials could have potential applications as permanent hard magnets and data storage media.     

ZnS:Cu polymer nanocomposites for thin film electroluminescent devices

Copper-doped zinc sulphide nanoparticles with varying copper content were synthesized via a coprecepitation method and embedded in polymer thin films by phase transfer technique to examine direct current electroluminescence (DC-EL) properties. A single layer structure (ITO/ZnS:Cu@ polymer/Al) was chosen to examine the influence of film thickness, copper content and polymeric matrix. Two types of devices were investigated based either on an insulating polymethylmethacrylate (PMMA) matrix or a semiconducting poly(9-vinylcarbazole) (PVK) matrix. The resulting DC-EL differs in spectral characteristics showing a broad EL emission over the whole visible range for PMMA based devices and EL with narrow full width at half-maxima values (FWHM) and maxima positions close to those observed in photoluminescence (PL) spectra of particle dispersions.     

Localized-surface-plasmon enhanced emission from porous silicon by gold nanoparticles

The porous silicon (PS) samples, decorated by Au nanoparticles (NPs) possessing localized-surface-plasmon (LSP) resonance, are prepared by the conventional anodization method. Photoluminescence (PL) is studied systematically, in particular, its dependence on the excitation power. It is found that undecorated PS samples exhibit a saturation behavior in PL intensity with increasing the pumping laser power, while the luminescence of Au-decorated PS hybrid samples have a purely linear dependence on the excitation power. In the linear response region of PS samples, addition of metal NPs layer moderately suppresses the emission while, in the saturation region, the net emission is enhanced by approximately up to 4-fold. Several possible mechanisms are discussed. We believe that the observed PL enhancement in saturation region is dominantly due to the resonant coupling between the LSP of Au NPs and the electronic excitation of PS, which inhibits the nonradiative Auger recombination process at high excitation power. These results indicate that the plasmon effect could be useful for designing even more efficient optoelectronic devices such as super bright light emitting devices and solar cells with high efficiencies. Despite many challenges, Au NPs can potentially be applied to introduce LSP resonance for the future silicon-based optoelectronics or photonics.     

Preparation of nanocomposites resin from seed Pterodon emarginatus doped maghemite nanoparticles

Electrical characterization and magnetic nanocomposite resin seeds Pterodon emarginatus (PE) doped with nanoparticles of maghemite and treated by different chemical processes is reported in this paper. The pure PE resin showed semiconducting characteristics probably the presence of natural iron oxide in its molecular structure. The analysis of M?ssbauer spectra pure resin showed two magnetic sites presented on measurements made at temperature of 300 K. Six "LEDs" to have been doped maghemite nanoparticles forming concentrations of 2.6 x 10(15) to 1.56 x 10(16) particles/cm2 forming the LED-PEMN. In the presence of the applied current versus voltage (0 to 0.9 V) LED-PEMN shown semiconducting properties. In the presence of frequency versus voltage sample of pure resin and LED features small decrease. While samples of LED-PEMN suffers loss frequency linearly with concentration and voltage. The pure PE resin shows high resistance to the applied voltage while the LED-PEMN is observed linear increase with the strength and concentration of nanoparticles of maghemite.     

Plasmonic properties of gold nanoparticles separated from a gold mirror by an ultrathin oxide

That a nanoparticle (NP) (for example of gold) residing above a gold mirror is almost as effective a surface enhanced Raman scattering (SERS) substrate (when illuminated with light of the correct polarization and wavelength) as two closely coupled gold nanoparticles has been known for some time. The NP-overmirror (NPOM) configuration has the valuable advantage that it is amenable to top-down fabrication. We have fabricated a series of Au-NPOM substrates with varying but thin atomic layer-deposited oxide spacer and measured the SERS enhancement as a function of spacer thickness and angle of incidence (AOI). These were compared with high-quality finite-difference time-domain calculations, which reproduce the observed spacer thickness and AOI dependences faithfully. The SERS intensity is expected to be strongly affected by the AOI on account for the fact that the hot spot formed in the space between the NP and the mirror is most efficiently excited with an electromagnetic field component that is normal to the surface of the mirror. Intriguingly we find that the SERS intensity maximizes at ~60° and show that this is due to the coherent superposition of the incident and the reflected field components. The observed SERS intensity is also shown to be very sensitive to the dielectric constant of the oxide spacer layer with the most intense signals obtained when using a low dielectric constant oxide layer (SiO(2)).     

A new and clean method on synthesis of gold nanoparticles from bulk gold substrates

In this work, we report a new pathway to prepare clean gold nanoparticles in neutral solutions with aid of natural chitosan. First, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1N NaCl and 1 g L^?1 chitosan from ?0.28 to +1.22 V vs. Ag/AgCl at 500 mV s^?1 for 200 scans. The durations at the cathodic and anodic vertices are 10 and 5 s, respectively. After this process, positively charged Au- and chitosan-containing complexes were produced in the solution. Then the solution was heated from room temperature to boiling at a heating rate of 6 °C min^?1 to prepare Au nanoparticles. The particle sizes of prepared Au (1 1 1) nanoparticles are ca. 10 nm. Moreover, the prepared Au nanoparticles in solutions are capable for anti-oxidation and stable in an ambient atmosphere for at least three months.