Rapid fabrication of Au nanoparticle films with the aid of centrifugal force

In this work, rapid fabrication of Au nanoparticle (Au NP) films has been simply achieved by alternate adsorption of citrate-stabilized Au NPs and poly(diallyldimethylammonium chloride) with the aid of centrifugal force. In contrast to conventional electrostatic assembly, we carried out the assembly process in a centrifuge with a rotating speed of 4000 rpm, where centrifugal force can be imposed on Au NPs. Scanning electron microscopy and cyclic voltammetry were employed to characterize the assembly procedure and the thus-prepared thin solid films. Our results demonstrate that centrifugal force can promote the assembly of Au NPs and therefore enable the rapid fabrication of functional Au NP films.

Performance Enhancement of Polymer Light-Emitting Diodes by Using Ultrathin Fluorinated Polyimide Modifying the Surface of Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)

Herein, an insulating fluorinated polyimide (F-PI) is utilized as an ultrathin buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in polymer light-emitting diodes to enhance the device performance. The selective solubility of F-PI in common solvents avoids typical intermixing interfacial problems during the sequential multilayer spin-coating process. Compared to the control device, the F-PI modification causes the luminous and power efficiencies of the devices to be increased by a factor of 1.1 and 4.7, respectively, along with almost 3-fold device lifetime enhancement. Photovoltaic measurement, single-hole devices, and X-ray photoelectron spectroscopy, are utilized to investigate the underlying, mechanisms, and it is found that the hole injection barrier is lowered owing to the interactions between the PEDOT:PSS and F-PI. The F-PI modified PEDOT:PSS layer demonstrates step-up ionization potential profiles from the intrinsic bulk PEDOT:PSS side toward the F-PI-modified PEDOT:PSS surface, which facilitate the hole injection.

Preparation of DNA - Silver nanohybrids in multilayer nanoreactors by in situ electrochemical reduction, characterization, and application

Novel nanocomposite films containing DNA-silver nanohybrids have been successfully fabricated by combined use of the layer-by-layer self-assembly technique and an in situ electrochemical reduction method with the DNA-Ag+ complex as one of the building blocks. UV-vis absorption spectroscopy was employed to monitor the buildup of the multilayer films, which suggested a progressive deposition with almost an equal amount of the DNA-Ag+ complex in each cycle. The following electrochemical reduction of silver resulted in the formation of metal nanoparticles in the film, which was evidenced by the evolution of the intense plasmon absorption band originating from silver. Scanning electron microscopy indicated that the particles formed in the multilayer films possessed good monodispersity and stability, thanks to the surrounding polymers. X-ray photoelectron spectroscopy further confirmed the presence of the main components (such as DNA and metallic silver) of the nanocomposite films. In addition, we show that the size of the metal nanoparticles and the optical property of the film could be readily tuned by manipulating the assembly conditions.

Synthesis and morphology of polyethylene chains grafted onto the surface of crosslinked polystyrene microspheres

The bifunctional comonomer 4-(3-butenyl) styrene was used to synthesize crosslinked polystyrene microspheres (c-PS) with pendant butenyl groups on their surface via suspension copolymerization. Polyethylene chains were grafted onto the surface of c-PS microspheres (PS-g-PE) via ethylene copolymerizing with the pendant butenyl group on the surface of the c-PS microspheres under the catalysis of metallocene catalyst. The composition and morphology of the PS-g-PE microspheres were characterized by means of Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. It is possible to control the content of PE grafted onto the surface of c-PS microspheres by varying the polymerization time or the initial quantity of pendant butenyl group on the surface of c-PS microspheres. Investigation on the morphology and crystallization behavior of grafted PE chains showed that different surface patterns could be formed under various crystallization conditions. Moreover, the crystallization temperature of PE chains grafted on the surface of c-PS microspheres was 6 degrees C higher than that of pure PE. The c-PS microspheres decorated by PE chains had a better compatibility with PE matrix.

pH-dependent conformational changes of ferricytochrome c induced by electrode surface microstructure

pH-dependent processes of bovine heart ferricytochrome c have been investigated by electronic absorption and circular dichroism (CD) spectra at functionalized single-wall carbon 'nanotubes (SWNTs) modified glass carbon electrode (SWNTs/ GCE) using a long optical path thin layer cell. These methods enabled the pH-dependent conformational changes arising from the heme structure change to be monitored. The spectra obtained at functionalized SWNTs/GCE reflect electrode surface microstructure-dependent changes for pH-induced protein conformation, pK(a) of alkaline transition and structural microenvironment of the ferricytochrome c heme. pH-dependent conformational distribution curves of ferricytochrome c obtained by analysis of in situ CD spectra using singular value decomposition least square (SVDLS) method show that the functionalized SWNTs can retain native conformational stability of ferricytochrome c during alkaline transition.

2D NMR and FT-Raman spectroscopic studies on the interaction of lanthanide ions and Ln-DTPA with phospholipid bilayers

The interactions of lanthanide ions and the Ln-DTPA (DTPA = diethylenetriaminepentaacetate) complex with di palmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) bilayers are studied by 2D NOESY and FT-Raman spectroscopy. Proton NMR spectroscopic results show that lanthanide ions combine with phosphate groups in the polar region of the outer layer of DPPC liposomes, leading to the separation in chemical shift of the proton signal of N(CH3)(3) The conformational change of the O-C-C-N+ backbone from the gauche conformer to the trans one is not found; i.e., the orientation of the polar headgroup is still parallel to the surface of the bilayers. The Ln-DTPA complex at low concentration in a pH 7.4 solution localizes far away from bilayers and thereby has little effect on the structure of bilayers. The FT-Raman spectroscopic results indicate that lanthanide ions affect strongly the fluidity of acyl chains of DPPE bilayers while the Ln-DTPA complex affects it slightly.

NMR and FT-Raman studies on the interaction of lanthanide ions with sphingomyelin bilayers

The interactions of lanthanide ions with sphingomyelin bilayers have been studied by using 2D NOESY spectroscopy and FT-Raman spectroscopy methods. The results indicate that lanthanide ions, as well as divalent calcium, combine mainly to the phosphate group in the polar headgroup and do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers. The polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer.

Coadsorption of nitric oxide and oxygen on the Ag(110) surface

The coadsorption of NO and O-2 on Ag(110) surface has been studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and in situ Raman spectroscopy. The existence of oxygen enhances the adsorption of NO by forming the NOx species, that is, NO2 and NO3, and the NO in turn as a promotor facilitates the cleavage of the dioxygen bond, forming the surface atomic oxygen species having the same spectral characteristics as those produced using oxygen at high pressure. The oxygen species generated by the interaction is composed of two parts. One is produced directly by the decomposition of surface NO-O-2 complex at ca 625 K, which raised an O 1s feature at 530.5 eV and is absent at ca 800 K, while the another with an O 1s binding energy of 529.2 eV emerges at higher temperatures and shows similar properties as the reported gamma-state oxygen which bound tightly on restructured silver surface. The exposure to NO and O-2 causes noticeable changes in the morphology of the Ag(110) surface and the flat terraces superseded by small (ca 0.1 mu m) pits, and particles with typical diameters of a few micrometres were formed at elevated temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.

Gold nanoparticles on polarizable surfaces as Raman scattering antennas.

Surface plasmons supported by metal nanoparticles are perturbed by coupling to a surface that is polarizable. Coupling results in enhancement of near fields and may increase the scattering efficiency of radiative modes. In this study, we investigate the Rayleigh and Raman scattering properties of gold nanoparticles functionalized with cyanine deposited on silicon and quartz wafers and on gold thin films. Dark-field scattering images display red shifting of the gold nanoparticle plasmon resonance and doughnut-shaped scattering patterns when particles are deposited on silicon or on a gold film. The imaged radiation patterns and individual particle spectra reveal that the polarizable substrates control both the orientation and brightness of the radiative modes. Comparison with simulation indicates that, in a particle-surface system with a fixed junction width, plasmon band shifts are controlled quantitatively by the permittivity of the wafer or the film. Surface-enhanced resonance Raman scattering (SERRS) spectra and images are collected from cyanine on particles on gold films. SERRS images of the particles on gold films are doughnut-shaped as are their Rayleigh images, indicating that the SERRS is controlled by the polarization of plasmons in the antenna nanostructures. Near-field enhancement and radiative efficiency of the antenna are sufficient to enable Raman scattering cyanines to function as gap field probes. Through collective interpretation of individual particle Rayleigh spectra and spectral simulations, the geometric basis for small observed variations in the wavelength and intensity of plasmon resonant scattering from individual antenna on the three surfaces is explained.

Development of sampling methods for Raman analysis of solid dosage forms of therapeutic and illicit drugs

The results of a study aimed at determining the most important experimental parameters for automated, quantitative analysis of solid dosage form pharmaceuticals (seized and model 'ecstasy' tablets) are reported. Data obtained with a macro-Raman spectrometer were complemented by micro-Raman measurements, which gave information on particle size and provided excellent data for developing statistical models of the sampling errors associated with collecting data as a series of grid points on the tablets' surface. Spectra recorded at single points on the surface of seized MDMA-caffeine-lactose tablets with a Raman microscope (lambda(ex) = 785 nm, 3 mum diameter spot) were typically dominated by one or other of the three components, consistent with Raman mapping data which showed the drug and caffeine microcrystals were ca 40 mum in diameter. Spectra collected with a microscope from eight points on a 200 mum grid were combined and in the resultant spectra the average value of the Raman band intensity ratio used to quantify the MDMA: caffeine ratio, mu(r), was 1.19 with an unacceptably high standard deviation, sigma(r), of 1.20. In contrast, with a conventional macro-Raman system (150 mum spot diameter), combined eight grid point data gave mu(r) = 1.47 with sigma(r) = 0.16. A simple statistical model which could be used to predict sigma(r) under the various conditions used was developed. The model showed that the decrease in sigma(r) on moving to a 150 mum spot was too large to be due entirely to the increased spot diameter but was consistent with the increased sampling volume that arose from a combination of the larger spot size and depth of focus in the macroscopic system. With the macro-Raman system, combining 64 grid points (0.5 mm spacing and 1-2 s accumulation per point) to give a single averaged spectrum for a tablet was found to be a practical balance between minimizing sampling errors and keeping overhead times at an acceptable level. The effectiveness of this sampling strategy was also tested by quantitative analysis of a set of model ecstasy tablets prepared from MDEA-sorbitol (0-30% by mass MDEA). A simple univariate calibration model of averaged 64 point data had R-2 = 0.998 and an r.m.s. standard error of prediction of 1.1% whereas data obtained by sampling just four points on the same tablet showed deviations from the calibration of up to 5%.

UV VIS AND RESONANCE RAMAN SPECTROELECTROCHEMICAL PROPERTIES OF TRANSITION-METAL CENTERS IMMOBILIZED WITHIN A POLY(AMINO ACID) MATRIX - ILLUSTRATED WITH AN IRON PORPHYRIN

An iron prophyrin complex has been immobilized on the surfaces of platinum, silver, and indium doped-tin oxide coated glass by using the poly(gamma-ethyl L-glutamate)-N-(3-aminopropyl)imidazole derivative 1 as a linking agent, thus allowing-the surface-enhanced resonance Raman and UV-VIS absorption spectra and electrochemical properties of the porphyrin to be studied in solvents in which it is not normally soluble.

The potential of electron beam radiation for simultaneous surface modification and bioresorption control of PLLA

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the fields of tissue engineering and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), Llactide/DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid (PLGA)). This work investigates the further potential of ebeam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. PLLA samples were subjected to e-beam treatments in air, with varying beam energies and doses. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy. Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA (as predicted). However, e-beam effects on surface properties were not shown to be dependent on beam energy or dose. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment.

Controlling Subnanometer Gaps in Plasmonic Dimers Using Graphene

Graphene is used as the thinnest possible spacer between gold nanoparticles and a gold substrate. This creates a robust, repeatable, and stable subnanometer gap for massive plasmonic field enhancements. White light spectroscopy of single 80 nm gold nanoparticles reveals plasmonic coupling between the particle and its image within the gold substrate. While for a single graphene layer, spectral doublets from coupled dimer modes are observed shifted into the near-infrared, these disappear for increasing numbers of layers. These doublets arise from charger-transfer-sensitive gap plasmons, allowing optical measurement to access out-of-plane conductivity in such layered systems. Gating the graphene can thus directly produce plasmon tuning.

Plasmon enhanced fluorescence studies from aligned gold nanorod arrays modified with SiO2 spacer layers

Here, we demonstrate that quasi self-standing Au nanorod arrays prepared with plasma polymerisation deposited SiO2 dielectric spacers support surface enhanced fluorescence (SEF) while maintaining high signal reproducibility. We show that it is possible to find a balance between enhanced radiative and non-radiative decay rates at which the fluorescent intensity is maximized. The SEF signal optimised with a 30 nm spacer layer thickness showed a 3.5-fold enhancement with a signal variance of <15% thereby keeping the integrity of the nanorod array. We also demonstrate the decreased importance of obtaining resonance conditions when localized surface plasmon resonance is positioned within the spectral region of Au interband transitions. Procedures for further increasing the SEF enhancement factor are also discussed.