Tokuji Miyashita

Preparation of lactose–silk fibroin conjugates and their application as a scaffold for hepatocyte attachment

We prepared glycoconjugates (Lac-CY-SF) by the homogeneous chemical modification of solubilized silk fibroin (SF) with lactose bearing the galactose residue using cyanuric chloride (CY) as a coupling spacer and examined the usefulness of their application as a scaffold for hepatocyte attachment. The covalent immobilization of lactose into SF was assessed by several criteria including 1H-NMR measurements and reactions with lectins such as Ricinus communis agglutinin (RCA(120)) and fluorescein isothiocyanate-labeled RCA(120) (FITC-RCA(120)). The 1H-NMR spectrum of Lac-CY-SF showed new broad peaks attributed to methine and methylene protons of lactose, and by the integrated intensities of the peaks the weight ratio of lactose to SF in Lac-CY-SF was determined to be 0.20. Addition of RCA(120) to Lac-CY-SF solution caused an increase in the turbidity of the Lac-CY-SF solution. Incubation of Lac-CY-SF films with FITC-RCA(120) showed that the fluorescence emitted from the whole surface of Lac-CY-SF films. Furthermore, we examined the effect of the Lac-CY-SF conjugate-coating onto polystyrene culture dishes on the attachment of rat hepatocytes and their morphology. Attachment of hepatocytes onto the 0.1% (w/v) conjugate-coated dishes showed about an 8-fold increase as compared with that on uncoated dishes, being comparable to that on collagen-coated dishes, whereas the attachment on the SF-coated dishes was lower than that on uncoated dishes. Hepatocytes cultured onto the conjugate-coated dishes for 2.5 h showed smaller round-shaped morphology compared to those on collagen-coated dishes. After 2 days of culture in medium containing 100 nM insulin and 100 nM dexamethasone, hepatocytes on the conjugate-coated dishes formed monolayer islands with a slightly dispersed morphology, while hepatocytes cultured on collagen-coated dishes were uniformly spread flat. These results indicate that the Lac-CY-SF conjugates are useful as a scaffold for hepatocyte attachment, but the morphology of hepatocytes cultured on the conjugate-coated dishes is different from that on collagen-coated dishes.

Effective photoinduced electron transfer in hetero-deposited redox polymer LB films

The spatial arrangement of the ruthenium dipyridyl complex and ferrocene derivative in heterodeposited redox polymer Langmuir−Blodgett (LB) films is used for the direction control of the photocurrent flow resulting from the photoinduced electron-transfer reaction and the high quantum efficiency. Two kinds of heterodeposited structures are constructed by varying the deposition order of these redox polymer monolayers by the LB technique. The cyclic voltammograms of the heterodeposited redox polymer LB films show current rectifying and charge storage properties. On light irradiation, the anodic photocurrent is observed at the heterodeposited redox polymer LB films consisting of Ru copolymer LB film as an inner layer and Fc copolymer LB film as an outer layer on the ITO (Fc/Ru/ITO) electrodes, whereas a cathodic photocurrent is observed at the reverse layered structure (Ru/Fc/ITO) electrodes. The direction of photocurrent flow depends on the deposition order of the redox polymer LB films on the ITO electrode....

Novel optical oxygen sensing material: platinum porphyrin-fluoropolymer film

New fluoropolymers, poly(isobutylmethacrylate-co-trifluoroethylmethacrylate) (poly-IBM-co-TFEM) and poly(styrene-co-trifluoroethylmethacrylate) (poly-styrene-co-TFEM) are synthesized and applied to the matrix of optical oxygen pressure sensing based on phosphorescence quenching of platinum porphyrin, platinum octaethylporphyrin (PtOEP), by oxygen. The I0/I100, as a sensitivity of the sensing film, where I0 and I100 represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively, of PtOEP-poly-IBM film and polystyrene film, as the reference, are estimated to be 69.0 and 4.5, respectively. However, the I0/I100 of poly-IBM-co-TFEM film and poly-styrene-co-TFEM film are estimated to be 288 and 296, respectively, and large Stern–Volmer constants are obtained. This result indicates that PtOEP-fluoropolymer films are highly sensitive devices for oxygen. For PtOEP-poly-IBM-co-TFEM film, response times are 6.0 sec for deoxygenated to oxygenated conditions and 35.1 sec for reverse conditions. For PtOEP-poly-styrene-co-TFEM film, however, response times are 4.4 sec for deoxygenated to oxygenated conditions and 30.2 sec for reverse conditions. The rapid response for switching between oxygenated and deoxygenated condition is accomplished using PtOEP-fluoropolymer film. Copyright

Fabrication of densely packed multi-walled carbon nanotube ultrathin films using a liquid–liquid interface

We describe the fabrication of a densely packed ultrathin film of multi-walled carbon nanotubes (MWCNTs) at a liquid–liquid interface. The MWCNTs, which were synthesized using an anodic aluminium oxide (AAO) film as a template, were dispersed in water. Then hexane was added to the dispersion to create the liquid–liquid interface. The MWCNTs were smoothly assembled at the interface to form an ultrathin film when ethanol was added to the MWCNT water dispersion/hexane solution. The ultrathin film can be transferred onto a solid substrate using the Langmuir–Blodgett deposition technique. With addition of 10 vol% ethanol to the solution, an ultrathin film of MWCNTs with coverage of about 70% was fabricated. The multilayer film was fabricated by repeated deposition of the ultrathin film.

Characterization of the molecular environment of polymer Langmuir-Blodgett films using a pyrene fluorescent probe

The molecular environment of polymer Langmuir−Blodgett (LB) films with different alkyl chain length, poly(N-dodecyl acrylamide) (pDDA) and poly(tert-pentyl acrylamide) (ptPA), which are copolymerized with a small amount of 1-pyrenylmethyl acrylate (PyMA) comonomer as a luminescent probe, was investigated by means of the surface pressure (π)−area (A) isotherms, UV−vis spectroscopy, and fluorescence spectroscopy. The pyrene ring orients perpendicular to the p(DDA/PyMA) layer in both the monolayer at the air/water interface and LB multilayers, while the pyrene moiety of p(tPA/PyMA) takes a parallel orientation to its layer plane. The pyrene residue is more exposed to its surroundings in p(tPA/PyMA) LB films and therefore sensitive to solvent polarity. The measurement of fluorescence anisotropy confirmed that the pyrene was densely packed in the LB films. These findings suggest that the molecular orientation of luminescent molecules can be controlled when the length of side chains is changed by only several a...

Photolithographic properties of ultrathin polymer Langmuir–Blodgett films containing anthracene moieties

This study investigated the unique photolithographic properties of poly(N-neopentyl methacrylamide-co-9-anthrylmethyl methacrylate) (p(nPMA-AMMA)) ultrathin films prepared by the Langmuir–Blodgett (LB) technique. The copolymer forms a stable monolayer on a water surface and LB films with any desired number of layers. The nPMA group in the LB film acts as a photodecomposition group under irradiation at 254 nm. On the other hand, photodimerization occurred between anthracene groups under irradiation at 365 nm. Consequently, positive-tone and negative-tone patterns were printed on a silicon wafer by choosing a suitable irradiation light wavelength. Etching resistance of p(nPMA-AMMA) LB films was also investigated in a nanometer regime permitting etching of gold or copper films.

Photofunctional thin film devices composed of polymer nanosheet assemblies

We have developed so-called polymer Langmuir–Blodgett (LB) films (polymer nanosheets) based on acrylamide polymer and its copolymers, and have reported a series of various functional polymer nanosheet assemblies. To fabricate photofunctional nanodevices, we have succeeded in the introduction of various photoactive chromophores such as redox species, aromatic hydrocarbons, optically nonlinear groups, and metal nanoparticles into polymer nanosheet assemblies. In this article, we focus on our recent topics of research, namely photo-electric conversion, optical logic gates based on photoinduced electron transfer, and plasmon coupling with metal nanoparticles in hybrid polymer nanosheet assemblies.

Free-standing ultrathin films with universal thickness from nanometer to micrometer by polymer nanosheet assembly

Fabrication of smooth and flexible free-standing films with universal thickness and a highly ordered layer structure is described in this paper. N-Dodecylacrylamide polymer forms a well-defined monolayer on a water surface. The acrylamide polymer chains are strongly associated by hydrogen bonding of amide groups in the monolayer, thereby forming a two-dimensional network (polymer nanosheet). The monolayer is transferable onto a substrate using the Langmuir–Blodgett (LB) method with regular deposition, even for more than 700 layers. The deposited polymer multilayers on a substrate where a sacrificial film had been coated in advance were peeled off safely in solution, yielding a free-standing film with a uniform thickness depending on the number of multilayers. Results showed that the film has a highly oriented layer structure in which the alkyl side chain orients vertically and the polymer backbone lies between the hydrophobic layers. The film thickness from nanometer scale to micrometer scale is controllable by various deposited layers maintaining a constant thickness (3.3 nm) per bilayer. A minimum free-standing ultrathin film with bilayer thickness (3.3 nm) was obtained. It resembles a biomembrane. Two-dimensional hydrogen bonding network formation between polymer backbones and molecular interaction between alkyl side chains contribute to the free-standing film formation and to its smooth surface.

Quasi-solid-state optical logic devices based on redox polymer nanosheet assembly.

We report fabrication of a quasi-solid-state optical logic gate based on a polymer nanosheet photodiode. Two amphiphilic copolymers, p(DDA/Ru) and p(DDA/Fc), which respectively have a ruthenium dipyridyl complex and a ferrocene derivative as a redox molecule, are synthesized to produce redox polymer nanosheets. To construct polymer nanosheet photodiodes, two redox polymer nanosheets were assembled onto an indium-tinoxide (ITO) electrode in a tailor-made manner. The ITO electrode was connected with a counter electrode using an agarose gel electrolyte. The simple two-electrode system performs as a quasi-solid-state polymer nanosheet photodiode (QS-PNP). The photocurrent flow direction of QS-PNP can be controlled to be anodic or be cathodic by changing the deposition order of the redox polymer nanosheets. The anodic and cathodic QS-PNPs were applied to construct optical OR and XOR logic gates. The OR logic gate was fabricated by connecting the anodic and cathodic QS-PNP in a series; XOR logic was fabricated by connecting two anodic QS-PNPs in series. In optical logic gates, excitations of p(DDA/Ru) were used as input signals, and photocurrent was used as an output signal. These optical logic gates operate in a quasi-solid-state in a simple two-electrode configuration, which facilitates integration of the logic elements.

Bottom-up Design of Hybrid Polymer Nanoassemblies Elucidates Plasmon-Enhanced Second Harmonic Generation from Nonlinear Optical Dyes

Flexible design of hybrid polymer nanoassemblies consisting of nonlinear optical (NLO) polymer nanosheets and gold nanoparticle alignment was done to elucidate near-field effects of localized surface plasmon (LSP) coupling, which was generated from coupled gold nanoparticles, on enhanced second harmonic generation (SHG) from nonlinear optical (NLO) dyes in hybrid nanoassemblies. Structurally well-defined hybrid polymer nanoassemblies comprising NLO polymer nanosheets and aligned gold nanoparticles were fabricated using bottom-up approaches: Langmuir-Blodgett (LB) technique and nanoparticle adsorption. Two hybrid polymer nanoassembled structures were particularly examined: a single-layer NLO polymer nanosheet and gold nanoparticle monolayer (single-layer structure) exhibiting intralayer LSP coupling, and a single-layer NLO polymer nanosheet sandwiched between two-layer gold nanoparticle monolayers (sandwich structure). The latter enables interlayer LSP coupling between the two gold nanoparticle monolayers. Dependence of SHG intensity on the distance between the NLO layer and nanoparticle layer was examined according to the LB layer structure and gold nanoparticle size variation. The SH light intensity from the NLO polymer nanosheet decreased almost exponentially with increasing spacer distance between the NLO polymer nanosheet and gold nanoparticle monolayer in both single-layer and sandwich structures. The decay length depends strongly on the gold nanoparticle size, indicating effective spatial distance for enhanced SHG from NLO polymer nanosheets. Theoretical calculations were used to study the enhancement mechanism. Finite difference time domain (FDTD) calculations reproduced the exponential behavior of SH light intensity as a function of separation distance, which confirmed the importance of coupled gold nanoparticle formation and parallel geometry of near-field coupling of the coupled gold nanoparticles with NLO polymer nanosheets for efficient SHG enhancement. Dipole-type LSP coupling along the long axis of adjacent gold nanoparticles at the fundamental frequency dominates enhancement of SHG from NLO dyes oriented parallel to the long axis of LSP coupling, which occurs at the center of the Au NPs.