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Papers - Fukui, Yuuka

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Preparation of a CNF porous membrane and in situ synthesis of silver nanoparticles (AgNPs)

Yuuka Fukui, Eriko Baba, Keiji Fujimoto

RSC Advances (Royal Society of Chemistry) 15 ( 2 ) 1115 - 1124 2025.01

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted

We prepared a cellulose nanofiber (CNF)-based porous membrane with three dimensional cellular structures. CNF was concentrated via a surfactant-induced assembly by mixing CNF with a cationic surfactant, domiphen bromide (DB). Furthermore, they were accumulated by centrifugation to obtain a CNF-DB sol. Next, when the CNF-DB sol was naturally dried, a membrane composed of densely packed CNF was obtained. On the other hand, when the CNF-DB sol was freeze-dried, a porous membrane with the anisotropic cellular structure could be obtained. The interspace between layered CNF sheets was tunable by the DB concentration in the assembly process and the centrifugal force in the accumulation process. FT-IR analysis of the porous membrane showed the formation of hydrogen bonds between the CNF, resulting in facilitation of crosslinking of the CNF and formation of the cellular structures. The obtained CNF-DB membrane exhibited high water resistance. They showed a high ability to absorb hydrophobic dyes such as Nile red and rhodamine B (RhB) due to the presence of the hydrophobic core of DB micelles. Then, the release of RhB could be controlled by the ionic strength in the medium. In addition, they possessed a high ability to adsorb cationic metals such as Ag ions due to the presence of carboxyl moieties of CNF. Next, in situ synthesis of silver nanoparticles (AgNPs) was carried out by employing the CNF-DB membrane as a template for Ag ion adsorption and reduction. Deposition of AgNPs could be observed on the CNF-DB membrane, which suppressed aggregation of AgNPs. Almost all AgNPs were arrayed apart from each other to generate the hotspots, which could enhance surface-enhanced Raman scattering (SERS) of AgNPs. Such an AgNPs-CNF composite membrane could be applied for a label-free analysis of adsorbed RhB.

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Preparation of a robust and degradable nanocapsule by polymer deposition over the liposome for loading and release of cargos

Fukui Y., Ito J., Takeiri M., Fujimoto K.

Colloids and Surfaces A: Physicochemical and Engineering Aspects (Colloids and Surfaces A: Physicochemical and Engineering Aspects) 676 2023.11

ISSN 09277757

We prepared biobased nanocapsules by the polymer deposition over the ceramide-containing liposomes to render abilities to load versatile substances and to release them in response to enzymatic degradation of the capsule wall. First, we carried out phosphorylation of chitosan (CHI) to make it amphoteric. Then, we prepared a liposome containing glucosylceramide (GlcCer) and carried out deposition of phosphorylated chitosan (PCHI). The obtained capsule showed high structural stability against solubilization by surfactants and organic solvents, where it maintained its size even in 90 vol% DMSO. Next, we attempted to load various substances into the capsule. A lipophilic Nile red dissolved in 50 vol% DMSO could be loaded into the capsule without rupturing. The loading capacity of PCHI-deposited liposomes was almost three times higher than that of bare liposomes. Its release was suppressed to less than 10 % in an aqueous solution, whereas it could be released to more than 40 % when a small amount of surfactant was added to mimic a lipophilic environment. Also, an amphoteric nature of the capsule derived from PCHI allowed for loading of both cationic and anionic substances. Furthermore, lysozyme (Lyso) was deposited onto the capsule to provide the capsule wall with the enzymatic degradability. Although the release of substances from the capsule was suppressed to less than 10 % without Lyso, it was increased to approximately 50 % by enzymatic degradation of the PCHI layer.

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One-pot generation of gold-polymer hybrid nanoparticles using a miniemulsion reactor system

Yuuka Fukui, Kaori Fujino, Keiji Fujimoto

Colloids and Surfaces A: Physicochemical and Engineering Aspects (Elsevier) 666 2023.06

Research paper (scientific journal), Joint Work, Corresponding author, Accepted, ISSN 09277757

We investigated one-pot synthesis of gold nanoparticles (AuNPs) and AuNPs-polymer hybrid nanoparticles in a water-in-oil (W/O) miniemulsion. Water nanodroplets were dispersed as a reactor in cyclohexane using dimethicone as a surfactant. First, we intended to generate AuNPs in water nanodroplets, which contained HAuCl4 with a mixture of 1-vinylpyrrolidone (VP) and N,N’-methylenebisacrylamide (MBAAm). Several AuNPs with the size of approximately 10–20 nm were generated in each nanodroplet via reduction of AuCl4- by dimethicone. On the other hand, AuNPs was scarcely generated in water nanodroplets containing HAuCl4 with 2-hydroxyethyl methacrylate (HEMA). Next, we carried out polymerization in water nanodroplets to encapsulate AuNPs into polymer nanoparticles. Several AuNPs were encapsulated within polymer particles by copolymerization of VP and MBAAm with an oil-soluble initiator (V-601), and some AuNPs were present in the oil phase. The encapsulation efficiency of AuNPs was 34%. The encapsulation efficiency of AuNPs was dramatically increased by increasing the concentration of the initiator. The same result was obtained by increasing the concentration of the crosslinker due to rapid gelation of nanodroplets. On the other hand, monodisperse particles could be obtained by polymerization of HEMA using a water-soluble initiator (V-65). After polymerization for 5 d at 65ºC, the color of the suspension changed from opaque blue to blue purple and the encapsulation efficiency of AuNPs (5–20 nm) increased to 99 wt%. The average number of AuNPs encapsulated in a PHEMA nanoparticle increased from 1.5 to 4.6 particle. Furthermore, the size of AuNPs could be tuned by increasing the HAuCl4 concentration, and the corresponding color of the suspensions such as blue, purple, and red could be observed. The number and location of AuNPs in polymer nanoparticles could also be tuned by additives such as L-histidine and polyvinylpyrrolidone. By drop-casting the obtained hybrid nanoparticles, we could obtain gold-polymer hybrid films where AuNPs were evenly distributed within a film. The films exhibited different colors corresponding to their LSPR of AuNPs.

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Control in Coloration and Estimation of the Refractive Index by Porous Polymeric Membranes Prepared by the "Miniemulsion" Templating Method

Fukui Y., Sumida H., Sugaya Y., Fujimoto K.

ACS Applied Polymer Materials (ACS Applied Polymer Materials) 4 ( 10 ) 7547 - 7553 2022.10

We fabricated porous polymeric membranes using the miniemulsion templating method to investigate the transmitted and scattered lights in terms of the Christiansen filter effect. This method made it possible to produce porous polymeric membranes with different refractive indices by polymerization of different monomers and copolymerization of monomers. When a membrane with an open-cellular structure was immersed in a liquid, the transmitted light was observed at a wavelength where the refractive indices of the polymeric phase and the liquid matched. Angle-independent color derived from the scattered light could also be observed. When the porous membrane of poly(2-ethylhexyl methacrylate) (EHMA) was immersed in a mixture of different kinds of liquids, the maximum wavelength of the transmission (λmax) changed according to the refractive index matching of the polymeric phase and the liquid, resulting in the change in coloration. Next, when the P(EHMA-co-EGDMA) membrane was immersed in a mixture of toluene and d-limonene, λmax and color varied depending on their mixing ratios. This coloration was controlled by temperature and the refractive indices of the polymeric phase and the liquid. Furthermore, we could estimate the refractive index of PEGDMA using λmax values obtained by immersing it into liquids with different refractive indices.

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Functionalization of keratin nanoparticles by their internal modifications

Yuuka Fukui, Kaori Ito, Keiji Fujimoto

Polymer Journal (Springer Nature) 54 ( 11 ) 1367 - 1375 2022.06

Research paper (scientific journal), Joint Work, Corresponding author, Accepted, ISSN 00323896

We prepared keratin nanoparticles, which could respond to temperature and pH changes and to redox reactions, by electrostatic association of keratin and a cationic surfactant, dioctadecyl dimethyl ammonium chloride (DODAC). Solubilized keratin chains were assembled into nanoparticles (Ker-DODAC) and then crosslinked by disulfide formation. The resultant nanoparticles (Ker-DODACss) possessed a hydrophobic core composed of DODAC, enabling hydrophobic compounds to be loaed and retained in the core. By increasing the temperature, the fluidity of the core was increased, resulting in Ker-DODACss swelling and burst release of loaded compounds. Next, cholesterol was loaded into Ker-DODACss to modify the inner environment, such as the hydrophobicity and fluidity of the core. The nanoparticles (Ker-DODACss-Chol) exhibited reduced fluidity of the core and suppressed release of the payload. Furthermore, the release could be triggered by decreasing the electrostatic interaction between keratin and DODAC at pH values lower than 7.4. It was also found that Ker-DODACss-Chol possessed the ability to release payloads by breaking disulfide bonds. As a further internal modification, we incorporated a lipophilic antioxidant, α-tocopherol, into Ker-DODACss-Chol. It was confirmed that Ker-DODACss-Chol could act as a physical barrier to prevent α-tocopherol from undergoing oxidative degradation.

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Preparation of a deformable nanocapsule by living radical polymerization in a liposome

Fukui Y., Fukui A., Fujimoto K.

Polymer Journal (Polymer Journal) 54 ( 7 ) 893 - 901 2022

ISSN 00323896

We aimed to prepare an elastic nanocapsule by internal modification of a liposome with living radical polymerization. First, monomers and photoiniferters were encapsulated in liposomes. Then, UV light irradiation was used to conduct living radical polymerization in the liposomes. The obtained nanocapsules showed good absorption and retention of chemical substances depending on the binding ability to the incorporated polymers, and the absorption capacity could be controlled by the length and dissolved state of the polymer chains. In addition, dynamic morphological changes in the capsules were observed when liposomes with high membrane fluidity were employed. Morphological changes in the nanocapsules were induced by altering the pH value and ionic strength, resulting in the release of cargo in response to these environmental conditions.

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Preparation of agarose xerogel nanoparticles by solvent evaporation from water nanodroplets

Fukui Y., Inamura R., Fujimoto K.

Polymer Journal (Polymer Journal) 53 ( 7 ) 815 - 821 2021.07

ISSN 00323896

We developed a W/O miniemulsion reactor system enabling the preparation of biopolymer nanoparticles and control of their morphologies and inner microstructures. First, the W/O miniemulsion was prepared by suspending water nanodroplets containing agarose in oil. Then, we produced agarose hydrogel nanoparticles (AgarH) by the gelation of agarose in nanodroplets. Next, we prepared agarose xerogel nanoparticles (AgarX) by precisely tuning the water evaporation from AgarH. We controlled the morphologies (solid and hollow) and crystal structure of AgarX by changing the pressure and temperature during water evaporation. In fact, AgarX with a hollow structure was generated through rapid evaporation at a low pressure. AgarH was dissolved in Milli-Q water when the temperature was raised to 90 °C. On the other hand, AgarX remained a solid particle under the same conditions, likely because of its high crystallinity. We expect that this technique can be applied to prepare xerogels of diverse biomass-based polymers for the replacement of synthetic polymers.

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Creation of porous polymeric membranes by accumulation of water nanodroplets in a miniemulsion system

Fukui Y., Fujino R., Sugaya Y., Fujimoto K.

Polymer Journal (Polymer Journal) 52 ( 9 ) 1077 - 1083 2020.09

ISSN 00323896

© 2020, The Society of Polymer Science, Japan. We developed a miniemulsion templating method to prepare porous polymeric membranes. First, water nanodroplets were suspended in an oil phase by using a nonionic and polymeric surfactant to form a water-in-oil (W/O) miniemulsion. After the nanodroplets accumulated by centrifugation, a small amount of monomer was added as an oil phase to resuspend the water nanodroplets in a monomer phase. Then, photopolymerization of the monomer phase was conducted to generate pores in the polymeric matrix. The size of the nanodroplets was tuned by the surfactant concentration to control the pore size of the membranes. We could produce pore morphologies such as closed-cellular, open-cellular, and bicontinuous structures by tuning the volume fraction of the nanodroplets. Alternatively, nanodroplets were accumulated by centrifugation, and then further surfactants were added to the monomer to suppress the coalescence of nanodroplets. This enabled us to generate a highly porous open-cellular structure while maintaining the size and spherical shape. Next, HAuCl4 was reduced by using the surfactant displayed at the inner surface of the pore wall as the reducing agent. Gold nanoparticles were produced in the inner pores of the polymeric membrane, showing coloration derived from local surface plasmon resonance.

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Tuning of particle indentation by surface modification of polymer particles and substrates

Fukui Y., Yamamoto K., Yamamoto T., Fujimoto K.

Colloids and Surfaces A: Physicochemical and Engineering Aspects (Colloids and Surfaces A: Physicochemical and Engineering Aspects) 588 2020.03

ISSN 09277757

© 2019 Elsevier B.V. We studied the influence of the chemical properties of the polymer particle and the polymer substrate on particle indentation. The polymer particles were arrayed over the polymer substrate and heat treatment (annealing) was conducted above the glass transition temperature (Tg) of bulk polymer to indent polymer particles into the polymer substrate. Surface topologies of particle-indented surfaces were observed with a field-emission scanning electron microscope (FE-SEM) and the degree of particle indentation (DI) was evaluated with a scanning probe microscope (SPM). The particle-arrayed substrate was placed upside down and then heat treatment was carried out. It was found that there was no effect of gravity on particle indentation. To prepare polymer particles with different chemical properties, surface grafting of hydrophobic, hydrophilic, cationic and anionic polymer chains was carried out by iniferter-initiated living radical polymerization. We found that the indentation of these particles was influenced by the outermost surface of the particle. Next, to investigate the effect of the substrate surface on particle indentation, sulfonation of the polystyrene (PS) substrate was carried out with concentrated sulfuric acid. We found that the surface property of the substrate also influenced particle indentation. From these results, we concluded that particle indentation would be determined by the interaction between the particle surface and the substrate surface. Finally, we intended to analyze the viscoelastic property of the substrate surface by particle indentation. We could estimate Tg values of PS and polyvinyl chloride (PVC) substrates by observing the particle indentation at the different annealing temperatures.

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Controlled release and targeting of polypeptide-deposited liposomes by enzymatic degradation

Fukui Y., Otsuka H., Fujimoto K.

Polymer Journal (Polymer Journal) 51 ( 11 ) 1223 - 1230 2019.11

ISSN 00323896

© 2019, The Society of Polymer Science, Japan. We prepared biobased nanocapsules with enzymatic degradability, which were generated by the layer-by-layer deposition of enzymes and polypeptide over the liposomal surface. Here, we demonstrate two different systems based on the enzymatic degradation of polymer layers. First, the deposition of trypsin and polyarginine (PArg), which is cleavable by trypsin, was carried out over a negatively charged liposome. The enzymatic cleavage of PArg resulted in exposure of the lipid membrane, which facilitated release of the cargo. Next, we attempted to degrade the outer polymer layer of the multilayered capsule wall to display the inner polymer layer by enzymatic degradation. This approach enabled the accumulation and targeting of the nanocapsules through the affinity between the displayed polymer layer and the target hydroxyapatite (HAp). The polymer wall was constructed with an inner layer consisting of poly-L-glutamic acid (PGlu) and an outer layer consisting of trypsin and PArg onto the liposome. The degradation of the outer PArg by trypsin allowed the surface to display the inner PGlu, which has bone-targeting ability. In addition, the polymer wall was constructed from an inner layer of PArg and an outer layer of pepsin and PGlu. The degradation of the outer PGlu by pepsin led to inner PArg on the surface to achieve cell-penetrating activity.

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Generation of mucin gel particles with self-degradable and -releasable properties

Fukui, Yuuka, Fukuda, Megumi, Fujimoto, Keiji

JOURNAL OF MATERIALS CHEMISTRY B (Journal of Materials Chemistry B) 6 ( 5 ) 781 - 788 2018.02

Research paper (scientific journal), Joint Work, ISSN 2050-750X

© The Royal Society of Chemistry 2018. Herein, we focused on mucin, which is a large viscous glycoprotein in terms of materials science, and reported preparation of mucin gel particles and incorporation of enzymes to provide the particle with self-degradable and releasable properties. To expose the hydrophobic peptide cores, trimming of sugar moieties was carried out by β-elimination reaction under alkaline conditions (tMucin). Nano-sized tMucin particles were prepared by the assembly of tMucin with the aid of a cationic surfactant. Then, cross-linking of tMucin particles was carried out via heat treatment (annealing) to induce thermal aggregation of the polypeptide chains. The hydrodynamic diameter of tMucin particles reversibly changed in response to calcium ions. Next, in an attempt to render the particle degradable, lysozyme was incorporated into the tMucin particles for the hydrolysis of oligosaccharide chains. These particles were gradually degraded upon enzymatic cleavage of the mucin molecules, facilitating the release of their incorporated substances. Also, the degradation of the mucin particles and the release of lysozyme were tunable by environmental conditions, such as temperature and calcium ions, in addition to the degree of cross-linking of the particles.

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Creation of hybrid polymer particles through morphological tuning of CaCO₃ crystals in miniemulsion system

Fukui Yuuka, Takamatsu Hideyuki, Fujimoto Keiji

Colloids and Surfaces A: Physicochemical and Engineering Aspects 516 1 - 8 2017.03

ISSN 0927-7757

We developed a miniemulsion-based nanoreactor system, which can allow for morphological tuning of CaCO₃ crystals in nanodroplets and their high encapsulation efficiency in polymer particles. We first obtained nano-sized CaCO₃ by using the aqueous nanodroplet as a nanoreactor. In addition, it was found that crystal growth and morphological transformation of CaCO₃ from spherical to rod-like crystals were induced by adding 2-hydroxyethyl methacrylate (HEMA) in nanodroplets. Such transformation was also promoted by raising the incubation temperature or increasing the number of nanodroplets in the presence of HEMA. We speculated that crystal growth of CaCO₃ crystals was induced by coalescence of nanodroplets and morphological transformation to rod-like shape was undertaken with an assistance of HEMA. In this way, we could tune the shapes of CaCO₃ with the well-controlled size and aspect ratio by tuning environments in nanodroplets. Then, subsequent polymerization of HEMA, which was used as a monomer, was carried out for encapsulation of CaCO₃ with rod-like morphologies inside polymer nanoparticles. As a result, spherical and spheroidal hybrid nanoparticles, which possessed homogeneity in size and shape, were obtained. Then, by spin-coating of hybrid nanoparticles onto the glass substrate, we could obtain a closely-packed particle monolayer.

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Preparation of free-standing hybrid colloidal membranes via assembly of liponanocapsules

Fukui Yuuka, Kameyama Shuhei, Fujimoto Keiji

Journal of Biomaterials Science, Polymer Edition (Taylor & Francis) 2017.02

Research paper (scientific journal), Joint Work, Accepted

Preparation of Liponanocapsules via Construction of Bio-Derived Capsule Wall on a Liposomal Template

Fukui, Yuuka

KOBUNSHI RONBUNSHU 74 ( 5 ) 396 - 409 2017

Research paper (scientific journal), ISSN 0386-2186

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Preparation of protein nano-objects by assembly of polymer-grafted proteins

Fukui Yuuka, Sakai Daiki, Fujimoto Keiji

Colloids and Surfaces B: Biointerfaces 148 503 - 510 2016.12

ISSN 0927-7765

We carried out surface-grafting from proteins and their assembling into objects with unique nanostructured materials (nano-objects). To immobilize polymer-initiating sites, amino groups of bovine serum albumin (BSA) were allowed to react with iniferter groups (BSA-i). Then, graft polymerization of N-isopropyl acrylamide (NIPAM) was performed by light-initiated living radical polymerization from immobilized iniferter moieties of BSA-i. The polymer-grafted BSA (BSA-g-PNIPAM) was assembled into nano-objects through the precipitation of PNIPAM graft chains and their sizes and morphologies were tuned by the chain length, the density and the chemical structure of graft polymers in addition to the environmental conditions such as temperature and pH. It was possible to retain the structures of nano-objects by thermal denaturation via heat treatment. Fluorescent substances were encapsulated in particulate nano-objects (nanoparticles) assembled from PNIPAM-g-BSA and their release could be regulated by tuning pH and temperature. Next, further graft polymerization from PNIPAM-grafted BSA was carried out by living radical polymerization of a cationic monomer, N,N-dimethylamino propyl acrylamide methyl chloride quaternary (DMAPAAQ). The grafted polymer was composed of a block copolymer of PNIPAM and a cationic polymer (PDMAPAAQ) and the gel-like nano-object was generated by increasing temperature. In contrast to PNIPAM-g-BSA, it became insoluble even when the temperature decreased, probably due to the electrostatic association between anionic regions of BSA and cationic regions of graft polymers. Coating of BSA-g-P(NIPAM-b-DMAPAAQ) enabled to form a uniform thin layer over a human hair. A free-standing membrane could be obtained by peeling from a water repellent substrate to create a porous membrane.

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Fine-tuning in mineral cross-linking of biopolymer nanoparticle for incorporation and release of cargo

Fukui Yuuka, Kabayama Narumi, Fujimoto Keiji

Colloids and Surfaces B: Biointerfaces 136 168 - 174 2015.12

ISSN 0927-7765

We developed a mineral cross-linking strategy to prepare a biopolymer-based nanoparticle using calcium phosphate (CaP) as a cross-linker. Nanoparticles were first formed by mixing deoxyribonucleic acid (DNA) with cationic surfactants, and were cross-linked by CaP precipitation. After removal of the surfactants, we carried out the alternative dialysis of nanoparticles against CaCl<inf>2</inf> aqueous solution and phosphate buffered solution for further mineral cross-linking. XRD and FT-IR studies revealed that the resultant nanoparticles were produced by mineral cross-linkages of hydroxyapatite (HAp) and the crystal amount and properties such as morphology and crystallinity could be well-controlled by the reaction conditions. Chemical dyes could be incorporated into nanoparticles via their affinities with crystal faces of HAp and DNA. Their release was tunable by crystal amount and properties of mineral cross-linkages. Also, the release could be triggered by mineral dissolution in response to pH. Such a mineral cross-linking will open up a potential way to provide a nanoparticle with versatile functions such as cleavable cross-linking, binding affinity for cargos, and pH-responsive release.

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Development of a particle nanoimprinting technique by core-shell particles

Watanabe H., Nishimura M., Fukui Y., Fujimoto K.

Langmuir 30 ( 6 ) 1630 - 1635 2014.02

ISSN 0743-7463

We developed a particle nanoimprinting technique assisted by the array of core-shell particles. Core-shell particles composed of a solid core of polystyrene and a soft shell were prepared by soap-free emulsion polymerization and subsequently seeded polymerization. By the Langmuir-Blodgett method, particles were arranged into a closely packed 2D array over the water surface and transferred onto a polystyrene (PS) substrate at a regular interval. The PS substrate was heated up above its glass transition temperature (T_g) by either UV irradiation using a high-pressure Hg lamp or heat treatment in a temperature-controlled incubator. It could be observed that a nanopatterned indented surface was formed through the denting of particles into the PS substrate (particle nanoindenting). By the detachment of particles from the substrate by ultrasonication in ethanol, nanoholes were produced over the surface (particle nanoimprinting). The depth and the wall of nanoholes and their interval were tunable by the shell thickness and the 2D packing ratio of core-shell particle monolayers. The contact angle decreased from 70 degrees of the pristine particle monolayer to 13 degrees by the particle nanoindenting, and again increased to 50 degrees by detaching the particles from the substrate to create the nanoholes. The use of nanoholes as zepto-litter volume vessels enabled us to produce and arrange nanocrystals, such as NaCl and CaCO ₃ (zepto-reactor). © 2014 American Chemical Society.

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Development of a Particle Nanoimprinting Technique by Core-Shell Particles

Watanabe Hideaki , Nishimura Midori , Fukui Yuuka, Fujimoto Keiji

Langmuir 30 ( 6 ) 1630 - 1635 2014.01

Preparation of nanometre-sized spiral mineral via controlled mineralization using a gel particle as a template

Fukui Yuuka, Nakada Saki, Fujimoto Keiji

RSC ADVANCES 4 ( 12 ) 6027 - 6030 2014

Research paper (scientific journal), ISSN 2046-2069

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One-pot synthesis of fluorescent hybrid nanoparticles and their assembly into transparent and multi-coloured nanofilms

FUKUI Yuuka, OZAWA Yui, FUJIMOTO Keiji

Journal of Materials Chemistry C 1 ( 6 ) 1231 - 1237 2012.12

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