Taiji Ikawa

Nanofabrication induced by near-field exposure from a nanosecond laser pulse

We demonstrate a photoinduced nanofabrication method, applicable to dimensions beyond the diffraction limit, by employing a nanosecond laser pulse with a high peak power. The second-harmonic wave of a Nd: yttrium–aluminum–garnet (YAG) laser with a 5 ns pulse width was irradiated onto the sample, which consisted of a hexagonal arrayed monolayer of nanoparticles on an azopolymer film. Topographical changes in the surface after irradiation were observed by atomic force microscopy. A transcription of the arrayed structure in the form of a dent structure was attained. In the case of 100 nm nanoparticles, the resolution of the transcription was beyond the diffraction limit. The dent depth and diameter were changed depending on the diameter of the nanoparticles and the irradiation power used. A depth analysis indicates a threshold for the ablation process.

Unconventional salt trend from soft to stiff in single neurofilament biopolymers.

We present persistence length measurements on neurofilaments (NFs), an intermediate filament with protruding side arms, of the neuronal cytoskeleton. Tapping mode atomic force microscopy enabled us to visualize and trace at subpixel resolution photoimmobilized NFs, assembled at various subunit protein ratios, thereby modifying the side-arm length and chain density charge distribution. We show that specific polyampholyte sequences of the side arms can form salt-switchable intrafilament attractions that compete with the net electrostatic and steric repulsion and can reduce the total persistence length by half. The results are in agreement with present X-ray and microscopy data yet present a theoretical challenge for polyampholyte interchain interactions.

Virus-templated photoimprint on the surface of an azobenzene-containing polymer.

A photoimprint-based immobilization process is presented for cylindrical viruses on the surface of an azobenzene-bearing acrylate polymer by using atomic force microscopy (AFM). Tobacco mosaic virus (TMV), 18 nm in diameter and ca. 300 nm in length, was employed as a model virus. First, a droplet of an aqueous solution containing TMV was placed on the acrylate polymer surface. After drying the droplet, the polymer surface was irradiated with light at a wavelength of 470 nm from blue-light-emitting diodes. Finally, the surface was washed by aqueous solution with detergents. The polymer surface was observed at each step by AFM. TMV was shown to embed itself gradually on the polymer surface during photoirradiation in a time scale of tens of minutes because of the formation of the surface groove complementary to the shape of TMV. Analysis of immobilization efficiency of TMV on the polymer surface by the immunological enzyme luminescence indicated that efficiency increased proportional to the photoirradiation time. In these experimental conditions, the absorption band of the azobenzene moiety remained constant before and after the photoirradiation. These results show that TMV is physically held on the complementary groove formed on the polymer surface by the photoirradiation.

Fluorescence from poly(N-vinylcarbazole) in uniaxially stretched polymer films

Steady-state and time-resolved fluorescence properties of poly(N-vinylcarbazole) (PVCz) dispersed in a polystyrene (PS) cast film were studied under tensile loadings at room temperature. The excited monomer emission of PVCz located around 350 nm decreased with increasing applied tensile strain from 0 to 0.8%. The strain enhanced the emission which was ascribed to the partial-overlap excimer of PVCz in a 360–430 nm region. The emission due to the full-overlap excimer of PVCz between 430 and 500 nm was unchanged by the action of the tensile loadings. The ratio of fluorescence intensities at 375 nm and 345 nm I375/I345 was proportional to the applied strain. The time-resolved fluorescence study indicated that the lifetimes of the excited monomer and of the partial-overlap excimer were not affected by the strain. The obtained results mean that the strain applied to the PS matrix increases the partial-overlap conformation of two adjacent carbazolyl chromophores in a PVCz chain and suggest that PVCz is a useful probe for detecting residual strains in polymer matrices.

Orientation Control of Photo‐Immobilized Antibodies on the Surface of Azobenzene‐Containing Polymers by the Introduction of Functional Groups

In our photo-induced immobilization technique for an antibody (IgG) using azopolymers, the introduction of COOH and NMe(2) into the azopolymers, which can introduce surface charges, strongly affected the immobilization properties such as the efficiency of immobilization and the activity of the immobilized IgG (i.e., the orientation of the immobilized IgG). The introduction of COOH promoted a more active orientation of the immobilized IgG. The orientation was determined during the adsorption process onto the azopolymer surface in solution before photo-immobilization, and was maintained during the photo-immobilization. The surface charge of the azopolymer appears to be an important factor for IgG orientation, which involves electrostatic interactions between its Fab and the azopolymer surface.

Area-selective photoimmobilization of a two-dimensional array of colloidal spheres on a photodeformed template formed in photoresponsive azopolymer film

We demonstrate that colloidal spheres can be arrayed on an azobenzene-containing polymer film, which has been patterned such that it forms a template, and that in a subsequent step, the spheres can be selectively photoimmobilized on the film. The steps were made possible by utilizing two photoresponsive properties of the polymer. The first is photoinduced surface deformation, which provides a patterned indented template. The spheres were organized on the surface in accordance with the template structure. The second is photoinduced immobilization, where small objects on the film are immobilized after irradiation. The area-selective immobilized patterns were obtained after washing.

Transcription of Near-Field Induced by Photo-Irradiation on a Film of Azo-Containing Urethane-Urea Copolymer

Abstract We present that an intensity distribution of optical near field induced around photo-irradiated polystyrene spherical nanopariticles was transcribed on a film of azo-containing urethane-urea copolymer. The transcription was attained by a topographical change of the polymer surface, and the change was observed using an atomic force microscope. We have observed distinguishable dent surface structure using particles 28 nm in diameter.

Fluorescence from soluble polythiophenes in uniaxially stretched polymers

Fluorescence behavior of poly(3-alkylthiophenes) (P3ATs) in poly(methyl methacrylate) (PMMA) films was studied under tensile loadings. The elastic deformation of the matrix induced by small strains up to 0.2% had a greater influence on time-resolved fluorescence rather than the steady-state one from P3ATs. The decay time of fluorescence decreased linearly as the applied stress was increased, and reached a minimum. We maintained that the attractive phenomenon for the time-resolved fluorescence under the tensile loadings was associated with distortion or deformation of the π-conjugated structure in P3AT chains having large molecular weight. When the applied strain exceeded the elastic limit of the matrix, the time-resolved or steady-state fluorescence behavior was unchanged. However, large elongation over 10% led to the red-shift of the steady-state fluorescence maximum and an increase in the decay time. These fluorescence properties, indicating the growth of the π-conjugation, were mainly governed by strain.

Polyamide 6 and high molecular weight phenol novolac blend having excellent mechanical properties in humid conditions

Polymer blends of polyamide 6 (PA6) and phenol novolac (PN) were prepared by melt mixing. Up to 30 wt% of high molecular weight PN (HPN) or low molecular weight PN (LPN) was blended with PA6, and the physical and mechanical properties were examined. The water absorption of PA6 is inhibited by PN, and this effect is independent of the molecular weight of PN. PA6 and PN are miscible, and their blends show a single glass transition temperature (T g) that is higher than that of PA6. HPN can enhance the T g of PA6 more efficiently than LPN because of its high T g. PA6 and the PA6/LPN blend after immersion in water had lower-than-room-temperature T gs transitioning to rubbery states. In contrast, the PA6/HPN blend after immersion in water had a higher-than-room-temperature T g. The PA6/HPN blend in water has excellent mechanical properties in its glassy state compared to those of PA6 in the dry state. Thus, the PA6/HPN blend can be used to broaden the applications of PA6, especially in humid conditions.

AFM Imaging of Biological Supramolecules by a Molecular Imprinting-Based Immobilization Process on a Photopolymer

Biologically derived molecules (biomolecules) are extremely diverse in their physical sizes, chemical and structural properties. They form supramolecular assemblies in vivo/vitro through noncovalent interactions (e.g., hydrogen bonding, hydrophobic interactions, π-π interactions, and/or electrostatic). The structures of the supramolecular assemblies change with the concentrations of salts and the biomolecules itself. Efficient immobilization of various biomolecules and their assemblies is a key aspect of many applications including microarray technologies, (Kambhampati (Ed.), 2003; Schena (Ed.), 2004) biotechnology in general (Mayers, 2002; Whitesides, 2001) and structural analysis based on AFM.