Alternate Soaking Technique for Micropatterning Alginate Hydrogels on Wettability-patterned Substrates.

Techniques for patterning hydrogels are important for fabrication of cell culture, analytical, and actuator devices at the micro- and nanometer length scales. In this study, we fabricated alginate hydrogels cross-linked by divalent cations on wettability-patterned substrates by alternate soaking of precursor solutions of sodium alginate and divalent cations. The wettability-patterned substrates were fabricated on hydrophilic glass plates modified with hydrophobic self-assembled monolayers of hexamethyldisilazane followed by exposure to an ultraviolet/ozone atmosphere through a metal mask. The film thickness of alginate gels with a width and length of 0.1 and 4 mm were tuned stepwise from 30 nm to 200 nm by adjusting the precursor conditions, including the pH, type of divalent metal ions, and sodium alginate concentration, and the alternate soaking conditions, including the dipping/withdrawal speed and number of alternate soaking cycles. This technique can be applied to other functional gels and will contribute to fabrication of hydrogel devices at the micro- and nanometer scales in the future.

Superhydrophobic Surfaces on Phase-separated Nanostructures of Polystyrene/Polymethyl Methacrylate Films Fabricated by the Double-spray Technique.

Rapid large-area printing techniques are required to fabricate superhydrophobic surfaces of polymer films on solid substrates. Here, we report a double-spray technique for fabrication of mixed phase-separated films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS-b-PMMA. The surface wettability of the films changes to superhydrophobic by immersing the samples in cyclohexane, which is a good solvent for only PS. The rinsing process forms nanostructures in the remaining PMMA films that have flat surfaces before the rinsing treatment. The highest contact angle is about 150° on the film with a PMMA ratio of 0.2. X-ray photoelectron spectroscopy shows that a small amount of PS remains on the surface of the PMMA films, making the films superhydrophobic. Addition of PS-b-PMMA to the PS/PMMA films forms smaller phase-separated structures than those in the original PS/PMMA films because of an increase in the compatibility between PS and PMMA. The contact angle hysteresis in the films decreases with increasing PS-b-PMMA ratio, indicating an increase in the homogeneity of the phase-separated structures.

Carbon Nanosheets by Morphology-Retained Carbonization of Two-Dimensional Assembled Anisotropic Carbon Nanorings.

Two-dimensional (2D) carbon nanomaterials possessing promising physical and chemical properties find applications in high-performance energy storage devices and catalysts. However, large-scale fabrication of 2D carbon nanostructures is based on a few specific carbon templates or precursors and poses a formidable challenge. Now a new bottom-up method for carbon nanosheet fabrication using a newly designed anisotropic carbon nanoring molecule, CPPhen, is presented. CPPhen was self-assembled at a dynamic air-water interface with a vortex motion to afford molecular nanosheets, which were then carbonized under inert gas flow. Their nanosheet morphologies were retained after carbonization, which has never been seen for low-molecular weight compounds. Furthermore, adding pyridine as a nitrogen dopant in the self-assembly step successfully afforded nitrogen-doped carbon nanosheets containing mainly pyridinic nitrogen species.

Molecular rotors confined at an ordered 2D interface.

Intramolecular rotation of molecules contained in a two-dimensional monolayer or a three-dimensional collapsed film at an air-water interface was investigated by in situ fluorescence spectroscopy of twisted intramolecular charge transfer (TICT) type 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) derivatives. The TICT type molecules, CCVJ-C12 and CCVJ-Chol, that contain a linear alkyl dodecyl chain or a cholesteryl group, respectively, as their hydrophobic group, were designed and synthesized to manipulate them at the air-water interface. These lipophilized molecular rotors showed the general properties of TICT molecules in solutions that the fluorescence intensity increases with increasing viscosity of the solvent, which is induced by inhibition of internal molecular rotations. The molecular rotors CCVJ-C12 and CCVJ-Chol formed monolayers at the air-water interface and in situ fluorescence spectroscopy was performed during the in-plane compression of the monolayers. It was revealed that the monomer emissions were suppressed and only after the collapse of monolayers, excimer emission from both layers consisting of CCVJ-C12 or CCVJ-Chol was observed. Suppressed monomer emission from monolayers suggests that intramolecular rotation is not inhibited in dense ordered monolayers. Furthermore, fluorescence spectroscopy of Langmuir-Blodgett (LB) films indicated that molecular rotations are not inhibited in the monolayer transferred on the solid substrates.

Regulated Drug Release Abilities of Calcium Carbonate-Gelatin Hybrid Nanocarriers Fabricated via a Self-Organizational Process.

In this study, we investigated the drug-releasing behavior of a calcium carbonate (CaCO3 )-gelatin hybrid nanocarrier, fabricated through a single process using biomimetic mineralization. The organic scaffold (gelatin) of the fabricated nanocarrier is responsible for its capacity to load anionic drugs and for controlling the morphology of the inorganic matrix (CaCO3 ). We studied the drug-releasing properties of the nanocarrier by investigating the response of the CaCO3 matrix to acidic conditions. We found that under neutral conditions, drug release from the nanocarrier was inhibited, whereas under acidic conditions, the drug was efficiently released. Therefore, drug release from the nanocarrier is largely dependent on the surrounding pH.

Alternate Spray-coating for the Direct Fabrication of Hydroxyapatite Films without Crystal Growth Step in Solution.

We discuss an alternate spray-coating technique for the direct fabrication of hydroxyapatite films using metal masks, suction-type spray nozzles and two calcification solutions of calcium hydroxide and phosphoric acid aqueous solutions. Hydroxyapatite films were formed only on the hydrophobic surface of the substrates. Scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the spray-coated films consisted of hydroxyapatite nanoparticles. The Ca/P ratio was estimated to be about 1.26. X-ray diffraction patterns of the spray-coated films almost coincided with those of the hydroxyapatite powders, showing that the spray-coated films consisted of hydroxyapatite nanoparticles. Dot arrays of hydroxyapatite films at a diameter of 100 µm were formed by tuning the concentrations of calcium hydroxide and phosphoric acid aqueous solutions. This technique allows for the direct fabrication of the hydroxyapatite films without crystal growth process in hydroxyapatite precursors, the scaffolds of crystal growth such as biocompatibility SiO2-CaO glasses, or electrophoresis processes. By using this technique, large-area ceramic films with biocompatibility will be micropatterned with minimized material consumption, short fabrication time, and reduced equipment investments.

Specificity of MicroRNA Detection on a Power-free Microfluidic Chip with Laminar Flow-assisted Dendritic Amplification.

MicroRNAs (miRNAs) are attracting considerable attention as potential biomarkers for the early diagnosis of cancer. We have been developing a detection method for miRNAs on a microfluidic chip with external-power-free fluid pumping and enzyme-free amplification. The assay is completed within 20 min. Here, we describe the specificity of this miRNA detection method. First, the specificity against mismatched sequences was investigated. The nonspecific detection of a 2-nucleotide mismatched sequence was negligible, while that of a 1-nucleotide mismatched sequence was observed to a reasonable extent. Next, the disturbance in mature miRNA detection by existence of its precursor miRNA was evaluated. One precursor miRNA out of four tested showed significant nonspecific responses at 1 nM or higher concentrations. However, those responses were much lower than that of the target mature miRNA at 0.1 nM. Finally, we tried to detect three endogenous miRNAs, which are known to be potential cancer biomarkers, in human leucocyte total RNA. The measured concentraions of these miRNAs agreed well with those obtained by quantitative reverse transcription polymerase chain reaction. These results indicate that the on-chip miRNA detection method has good specificity, which is promising for applications to real biological samples.

Alternate Calcification in Microcapillaries for the Fabrication of Hydroxyapatite Films without Light Exposure, Calcination, or Applied Voltage.

We discuss an alternate method for calcification in microcapillaries for fabricating calcium phosphate films using silicone molds and calcifying solutions. Calcium phosphate films with a line/space of 5-50 µm were fabricated by controlling the concentrations of calcium chloride and sodium phosphate solutions. Plate-type crystals of hydroxyapatite were grown when the calcium phosphate films were immersed in hydroxyapatite precursors. In the initial stage of hydroxyapatite crystal growth, the c-plane of the crystals was grown parallel to the substrates, and subsequently the growth followed with the c-plane growing perpendicular to the substrates. In narrow capillaries, dendritic structures were formed with a tendency to grow in a direction parallel to the direction of the microcapillaries. This technique is useful in the micropatterning of biocompatible ceramics with a minimized material consumption and a short fabrication time.

Detection of Methylated DNA on a Power-Free Microfluidic Chip with Laminar Flow-Assisted Dendritic Amplification.

We report on a detection method for methylated DNA on a microfluidic chip, which needs no external power for fluid pumping. The methylated DNA was sandwiched by immobilized probe DNA and an anti-methylcytosine antibody. The fluorescence signal was amplified by our original amplification technology. The detection method was first optimized using a 22-mer DNA sequence, then further validated using a 60-mer DNA sequence adapted from the SEPT9 gene. We were able to detect the methylated 60-mer DNA at 0.4 nM within 18 min.

Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field-Effect Transistors.

We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)4) from a chloroform solution. Aligned needle-shaped QQT(CN)4 crystals were formed in thin film microstructures using either open- or closed- capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm(2) V(-1) s(-1), respectively, approaching the values previously obtained in individual QQT(CN)4 single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)4 solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices.

Calcination-free micromolding in capillaries for nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets.

We report calcination-free micromolding in capillaries for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets. We prepared Er(3+)- and Yb(3+)-codoped NaYF4 nanoparticles modified with a cationic polymer to improve dispersion stability of aqueous dispersion of the NaYF4 nanoparticles. We controlled the line width and density of nanoparticles in the NaYF4 nanoparticle films on flexible plastic sheets by adjusting the concentrations of the NaYF4 nanoparticle dispersion and the channel sizes of silicone stamps, resulting in the formation of nanopatterned NaYF4 nanoparticle films at the line width of the nanoparticle size (50 nm). Visible upconversion luminescence and near-infrared fluorescence appeared from the NaYF4 nanoparticle films excited with a near-infrared laser beam. These results demonstrate that calcination free micromolding in capillaries using aqueous dispersion of NaYF4 nanoparticles modified with a cationic polymer allows for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets.

Soft liquid phase adsorption for fabrication of organic semiconductor films on wettability patterned surfaces.

We report a soft liquid-phase adsorption (SLPA) technique for the fabrication of organic semiconductor films on wettability-patterned substrates using toluene/water emulsions. Wettability-patterned substrates were obtained by the UV-ozone treatment of self-assembled monolayers of silane coupling agents on glass plates using a metal mask. Organic semiconductor polymer films were formed selectively on the hydrophobic part of the wettability-patterned substrates. The thickness of the films fabricated by the SLPA technique is significantly larger than that of the films fabricated by dip-coating and spin-coating techniques. The film thickness can be controlled by adjusting the volume ratio of toluene to water, immersion angle, immersion temperature, and immersion time. The SLPA technique allows for the direct production of organic semiconductor films on wettability-patterned substrates with minimized material consumption and reduced number of fabrication steps.

Triggered J-aggregation in mixed Langmuir-Blodgett films of amphiphilic spiropyran having a methoxy group at the 5' position and an azobenzene derivative.

Here, we describe the formation of J-aggregates triggered by isomerization of an azobenzene derivative, N-[p-[(p-dodecylphenylazo)phenyloxy]dodecylpyridinium bromide (AzP), in mixed Langmuir-Blodgett (LB) films that contain an amphiphilic spiropyran with a methoxy group at the 5' position, MeO-SP1822. Pure LB films of MeO-SP1822 consist of multilayer domains embedded in a monolayer. UV irradiation of the films causes the isomerization of MeO-SP1822 to its merocyanine form, MeO-MC1822. Pure LB films of AzP comprise finger-like domains and granular domains. Irradiating mixed films of MeO-SP1822 and AzP with alternating UV and visible light causes J-aggregation of MeO-MC1822, with the amount of J-aggregates reaching a maximum at a 1:1 molar ratio. J-aggregation occurs in flat finger-like structures originating in the AzP-rich granular domains that are located on top of the MeO-MC1822-rich multilayer domains. J-aggregates are also present under the AzP-rich granular domains, though these domains do not serve as nucleation sites for the finger-like structures. We propose that granular domains serving as nucleation sites are partially buried in the multilayer domains, whereas those triggering the J-aggregation of MeO-MC1822 under the granular domains are situated on top of the multilayer domains.

Physicochemical properties of oleic acid-based partially fluorinated gemini surfactants.

We have developed oleic acid-based partially fluorinated gemini surfactants with carboxylic acid headgroups. The fluorocarbon chain is covalently bound to the terminal carbonyl group of oleic acid via a -CH(2)CH(2)OCO- unit, and the carboxylic acid headgroups are introduced to the cis double bond of oleic acid via -OCOCH(2)CH(2)- units. The aqueous solution properties of these surfactants were studied at pH 9 in the presence of 10 mmol dm­3 NaCl by means of static surface tension, pyrene fluorescence, and dynamic light scattering measurements. The resulting surface tension data demonstrate that the partially fluorinated gemini surfactants exhibit excellent surface activity in their dilute aqueous solutions. In addition, the surfactants are suggested to form micellar aggregates 2­4 nm in diameter. We also studied the aqueous temperature-concentration phase diagrams of the partially fluorinated gemini surfactants (disodium salts) on the basis of visual observations (through a crossed polarizer), polarized optical microscopy, and small angle X-ray scattering measurements. Several phase states including micellar solution phase, hexagonal phase, bicontinuous cubic phase, and lamellar phase were observed along with the coexistence of these phases in certain regions. Assemblies with lesser positive curvature tend to be formed with increasing surfactant concentration, increasing temperature, and increasing fluorocarbon chain length. A comparison of the phase diagrams of the partially fluorinated and hydrogenated surfactant systems suggests that close molecular packing is inhibited within the assemblies of the partially fluorinated surfactants because of the limited miscibility between the fluorocarbon and hydrocarbon units. To the best of our knowledge, this is the first systematic report focusing on the temperature-concentration phase diagrams of (partially) fluorinated gemini surfactants over a wide range of compositions and temperatures.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets.

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV-ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er(3+) and Yb(3+)-codoped Y2O3 nanoparticles at a diameter of 100 nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

In situ KPFM imaging of local photovoltaic characteristics of structured organic photovoltaic devices.

Here, we discuss the local photovoltaic characteristics of a structured bulk heterojunction, organic photovoltaic devices fabricated with a liquid carbazole, and a fullerene derivative based on analysis by scanning kelvin probe force microscopy (KPFM). Periodic photopolymerization induced by an interference pattern from two laser beams formed surface relief gratings (SRG) in the structured films. The surface potential distribution in the SRGs indicates the formation of donor and acceptor spatial distribution. Under illumination, the surface potential reversibly changed because of the generation of fullerene anions and hole transport from the films to substrates, which indicates that we successfully imaged the local photovoltaic characteristics of the structured photovoltaic devices. Using atomic force microscopy, we confirmed the formation of the SRG because of the material migration to the photopolymerized region of the films, which was induced by light exposure through photomasks. The structuring technique allows for the direct fabrication and the control of donor and acceptor spatial distribution in organic photonic and electronic devices with minimized material consumption. This in situ KPFM technique is indispensable to the fabrication of nanoscale electron donor and electron acceptor spatial distribution in the devices.

Structures of langmuir-gibbs films consisting of long-chain fatty acid and water-soluble surfactants.

The structures of Langmuir-Gibbs (LG) films at the air-solution interface were studied using surface tensiometry, Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IR-ERS). The LG films were fabricated by forming Langmuir films of deuterated arachidic acid (D19A) and then injecting a water-soluble surfactant, sodium dodecyl sulfate or octaethylene glycol monododecyl ether, into the subphase. The presence of the LG films at the air-solution interface affected the surface tension of water. BAM observations revealed the formation of phase-separated monolayers consisting of D19A monolayers and expanded monolayers of water-soluble surfactant at low concentrations of the water-soluble surfactant. The presence of phase-separated structures was supported by the IR-ERS results. At high concentrations, the water-soluble surfactants adsorbed to the domains of D19A monolayers, forming bilayers under the monolayers. The IR-ERS results suggest the penetration of the water-soluble surfactants into the domains of D19A monolayers and the diffusion of D19A molecules into the bilayer regions of the water-soluble surfactants. At concentrations greater than the critical aggregate concentration and/or critical micelle concentration, D19A molecules were solubilized in the solution. In some cases, the multilayers were kinetically stabilized and were present even 24 h after the injection of the water-soluble surfactants into the subphase.

Micromolding in capillaries for calcination-free fabrication of flexible inorganic phosphor films consisting of rare-earth-ion-doped nanoparticles.

We discuss the micromolding in capillaries technique for the direct fabrication of calcination-free rare earth ion-doped (RE) phosphor films consisting of RE nanoparticles on plastic sheets. We synthesized two types of RE nanoparticles consisting of Y2O3 matrix doped with Er and Yb ions. Green upconversion luminescence, red upconversion luminescence, and near-infrared fluorescence appeared from the RE nanoparticles under excitation of near-infrared light. Adjusting the channel width and depth of polydimethylsiloxane molds led to control of the density of nanoparticles in the patterned RE nanoparticle films. Adjusting concentration of the RE nanoparticle dispersion and size of the RE nanoparticles allowed for the control of the density of nanoparticles in the patterned RE nanoparticle films. The density of nanoparticles in the patterned RE films on plastic sheets increased with an increase in the number of injection and drying of the RE nanoparticle dispersion. These results demonstrate that this technique enables us to directly fabricate the patterned RE phosphor films on plastic sheets, leading to the fabrication of inorganic flexible devices with small fabrication steps and material consumptions.

"Soft" liquid-phase adsorption for the fabrication of solution processable organic material films on wettability-patterned surfaces.

We discuss a "soft" liquid-phase adsorption (SLPA) technique for the fabrication of organic films on wettability-patterned templates by using methanol/hexane and toluene/water emulsions. The emulsions are stable for several hours at room temperature, and the diameters of the dispersed phase are estimated to be several micrometers using dynamic light scattering. The templates are fabricated by exposing self-assembled monolayers to an ultraviolet/ozone atmosphere through a shadow mask. Fluorescent dye and semiconductor polymer films are formed selectively on the hydrophilic region of the substrates and the hydrophobic region of the self-assembled monolayer, respectively. The thickness is significantly larger than those of the films fabricated by conventional film-forming techniques such as spin-coating and dip-coating, respectively. These patterned films serve as photoluminescent films. These results demonstrate that the SLPA technique allows for the fabrication of organic films on wettability-patterned templates using solution-processable materials. This technique will find application to the fabrication of electronic and photonic devices with small material consumption and few film-forming processes.

Patterning of solution-processable materials on templates fabricated from mixed Langmuir-Blodgett films.

We report a useful lithographic technique for the fabrication of organic or metal films on wettability-patterned surfaces fabricated solely through self-assembly. The phase-separated structures in mixed Langmuir-Blodgett (LB) films can be tuned by adjusting intermolecular interactions in film-forming molecules such as fatty acids, hybrid carboxylic acids, and silane-coupling agents. Templates are fabricated from phase-separated mixed LB films and organic phosphor and metal films can be formed on the templates using casting, dip-coating, and solvent evaporation techniques. This methodology enables low-cost and low-energy fabrication of patterned films comprising solution-processable materials in small facilities.