A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)(n) films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O-2; as a result, they are more attractive compared to (CNT/polyelectrolyte)(n) and (NP/polyelectrolyte)(n) films because of their multifunctionality.

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.

Self-assembly of ionic liquids-stabilized Pt nanoparticles into two-dimensional patterned nanostructures at the air-water interface

In this paper, we demonstrate the self-assembly of ionic liquids (ILs)-stabilized Pt nanoparticles into two-dimensional (2D) patterned nanostructures at the air-water interface under ambient conditions. Here, ILs are not used as solvents but as mediators by virtue of their pronounced self-organization ability in synthesis of self-assembled, highly organized hybrid Pt nanostructures. It is also found that the morphologies of the 2D patterned nanostructures are directly connected with the quantities of ILs. Due to the special structures of ILs-stabilized Pt nanoparticles, 2D patterned Pt nanostructures can be formed through the pi-pi stack interactions and hydrogen bonds. The resulting 2D patterned Pt nanostructures exhibit good electrocatalytic activity toward oxygen reduction.

Kinetic study of DNA/DNA hybridization with electrochemical impedance spectroscopy

The hybridization of immobilized oligonucleotides probe strands with solution phase targets is the underlying principle of microarraybased techniques for the analysis of DNA variation. To study the kinetics of DNA/DNA hybridization, target DNA is often prior labeled with markers. A label-free method of electrochemical impedance spectra (EIS) for study the hybridization in process was reported. The Langmuir model was used to determine the association rate constant (K-on), the dissociation rate constant (K-off) and the affinity rate constant (K-A), for perfect matched DNA hybridization. The results show that, EIS is a successful technique possessing high effectivity and sensitivity to study DNA/DNA hybridization kinetics. This work can provide another view on EIS for the studying of DNA/DNA hybridization.

Assembly of 12-tungstosilicic acid and 4-aminobenzo-15-crown-5 ether based on the electrostatic attraction through bridging of oxonium ions on different substrates

Based on the electrostatic attraction Keggin-type polyoxometalate H4SiW12O40 (SiW12) and small molecule 4-aminobenzo-15-crown-5 ether (4-AB15C5) were alternately deposited on poly (allylamine hydrochloride) (PAH)-derived indium tin oxide (ITO) substrate through a layer-by-layer (LBL) self-assembly, forming a supramolecular multilayer film (film-A). SiW12 was also deposited on a glassy carbon electrode (GCE) derived by 4-AB15C5 via covalent bonding in 0.1 M NaCl aqueous solution and formed a composite monolayer film (film-B). UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy measurements demonstrated that the interactions between SiW12 and 4-AB15C5 in both two film electrodes were the same and caused by the bridging action of oxonium ions. But, the nanostructure in the two film electrodes was different. 4-AB15C5 in film-A was oriented horizontally to ITO substrate, however, that in film-B was oriented vertically to GCE. Namely film-A corresponded to a layer structure, and film-B corresponded to an intercalation structure.

Fabrication and characterization of SERS-active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4-aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS-based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80-100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 x 10(4) relative to silver colloid, which might have resulted from the presence of 'hot-spots' at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 x 10(7) by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface.

Design of polymeric stabilizers for size-controlled synthesis of monodisperse gold nanoparticles in water

A new methodology is described for the one-step aqueous preparation of highly monodisperse gold nanoparticles with diameters below 5 nm using thioether- and thiol-functionalized polymer ligands. The particle size and size distribution was controlled by subtle variation of the polymer structure. It was shown that poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were the most effective stabilizing polymers in the group studied and that relatively low molar mass ligands (similar to 2500 g/mol) gave rise to the narrowest particle size distributions. Particle uniformity and colloidal stability to changes in ionic strength and pH were strongly affected by the hydrophobicity of the ligand end group. "Multidentate" thiol-terminated ligands were produced by employing dithiols and tetrathiols as chain-transfer agents, and these ligands gave rise to particles with unprecedented control over particle size and enhanced colloidal stability. It was found throughout that dynamic light scattering (DLS) is a very useful corroboratory technique for characterization of these gold nanoparticles in addition to optical spectroscopy and TEM.

Bifunctional magnetic-optical nanocomposites: Grafting lanthanide complex onto core-shell magnetic silica nanoarchitecture

Anew class of bifunctional architecture combining the useful functions of superparamagnetism and terbium complex luminescence into one material has been prepared via two main steps by a modified Stober method and the layer-by-layer (LbL) assembly technique. The obtained bifunctional nanocomposites exhibit superparamagnetic behavior, high fluorescence intensity, and color purity. The architecture has been characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis absorption and emission spectroscopy, X-ray diffraction, and superconducting quantum interference device (SQUID) magnetometry.

Assembly of one-dimensional organic luminescent nanowires based on quinacridone derivatives

The quinacridone derivatives N,N'-dialkyl-1,3,8,10-tetramethylquinacridone (CnTMQA, n = 6, 10, 14) were used as building blocks to assemble luminescent nano- and microscale wires. It was demonstrated that CnTMQA with different lengths of alkyl chains display obviously different wire formation properties. C10TMQA and C14TMQA showed a stronger tendency to form 1-D nano- and microstructures compared with C6TMQA. The C10TMQA molecules could be employed to fabricate the wires with different diameters, which exhibited a size-dependent luminescence property. The emission spectrum of the C10TMQA wires with diameters of 200-500 nm shows a broad emission band at 560 nm and a shoulder at around 535 nm, while the emission spectrum of the C10TMQA wires with diameters of 2-3 mu m reveals a narrower emission band at 563 nm. For the CnTMQA-based samples with different morphologies, the emission property change tendency agrees with that of the powder X-ray diffraction patterns of these samples.

Stimuli-responsive polyelectrolyte block copolymer brushes synthesized from the si wafer via atom-transfer radical polymerization

Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.

Dewetting of thin polystyrene films under confinement

The dewetting behavior of thin polystyrene (PS) film has been investigated by placing an upper plate with a ca. 140 nm gap from the underlying substrate with the spin-coated thin polymer films. Three different kinds of dewetting behaviors of thin PS film have been observed after annealing according to the relative position of the PS film to the upper plate. Since the upper plate is smaller than the underlying substrate, a part of the polymer film is not covered by the plate. In this region (I), thin PS film dewetting occurs in a conventional manner, as previously reported. While in the region covered by the upper plate (III), the PS film exhibits unusual dewetted patterns. Meanwhile, in the area right under the edge of the plate (II) (i.e., the area between region I and region III), highly ordered arrays of PS droplets are formed. Formation mechanisms of different dewetted patterns are discussed in detail. This study may offer an effective way to improve the understanding of various dewetting behaviors and facilitate the ongoing exploration of utilizing dewetting as a patterning technique.

Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding triton X-100

Our previous investigation showed that the ordered hexagonal island pattern in the phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/P2VP) formed due to the convection effect by proper control of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to P2VP. In this paper, we further illustrate that, by adding a proper amount of the surfactant Triton X-100 to the PS/P2VP toluene solution, the ordered hexagonal island pattern can be transformed to the ordered honeycomb pattern. The effects of the amount of Triton X-100 on the surface morphology evolution and the pattern transformation are discussed in terms of the collapse of Triton X-100, phase separation between Triton X-100/P2VP and PS, the interfacial interaction between Triton X-100/P2VP and the mica substrate, and the Benard-Marangoni convection.

Shape-gradient composite surfaces: Water droplets move uphill

The approach of water droplets self-running horizontally and uphill without any other forces was proposed by patterning the shape-gradient hydrophilic material (i.e., mica) to the hydrophobic matrix (i.e., wax or low-density polyethylene (LDPE)). The shape-gradient composite surface is the best one to drive water droplet self-running both at the high velocity and the maximal distance among four different geometrical mica/wax composite surfaces. The driving force for the water droplets self-running includes: (1) the great difference in wettability of surface materials, (2) the low contact angle hysteresis of surface materials, and (3) the space limitation of the shape-gradient transportation area. Furthermore, the average velocity and the maximal distance of the self-running were mainly determined by the gradient angle (alpha), the droplet volume, and the difference of the contact angle hysteresis. Theoretical analysis is in agreement with the experimental results.

Motion of integrated CdS nanoparticles by phase separation of block copolymer brushes

A new method of reversibly moving US nanoparticles in the perpendicular direction was developed on the basis of the phase separation of block copolymer brushes. Polystyrene-b-(poly(methyl methaerylate)-co-poly(cadmium dimethacrylate)) (PS-b-(PMMA-co-PCdMA)) brushes were grafted from the silicon wafer by surface-initiated atom transfer radical polymerization (ATRP). By exposing the polymer brushes to H2S gas, PS-b-(PMNlA-co-PCdNlA) brushes were converted to polystyrene-b-(poly(methyl methacrylate) -co-poly(methacrylic acid)(CdS)) (PS-b-(PMMA-co-PMAA(CdS))) brushes, in which US nanoparticles were chemically bonded by the carboxylic groups of PMAA segment. Alternating treatment of the PS-b-(PMMA-co-PMAA(CdS)) brushes by selective solvents for the outer block (a mixed solvent of acetone and ethanol) and the inner PS block (toluene) induced perpendicular phase separation of polymer brushes, which resulted in the reversible lifting and lowering of US nanoparticles in the perpendicular direction. The extent of movement can be adjusted by the relative thickness of two blocks of the polymer brushes.

Direct formation of giant vesicles from synthetic polypeptides

This report describes direct formation of giant vesicles from a series of poly(L-lysine)-block-poly(L-phenylalanine) (PLL-b-PPA) block copolymers from their water solution. These polymers are prepared by successive ring-opening polymerization (ROP) of the two alpha-amino acid N-carboxyanhydrides and then removing the side chain protecting groups by acidolysis. The structures of the copolymers are confirmed by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and size exclusion chromatography ( SEC). The vesicles are studied by atomic force microscopy (AFM), field emission scanning electron microscopy (ESEM), and confocal laser scanning microscopy (CLSM). Rhodamine B is used as a fluorescent probe to confirm the existence of the vesicle with an aqueous interior. The vesicle size is in the range 0.55-6 mu m, depending on the absolute and relative lengths of the two blocks, on initial polymer concentration, and on solution pH. The vesicles are still stable in water for 2 months after preparation. Addition of the copolymer to DNA solution results in complex formation with it. The complex assumes the morphology of irregular particles of less than 2 mu m. It is expected to be used in drug and gene delivery.