Motohiro Tagaya

Oxide-based inorganic/organic and nanoporous spherical particles: synthesis and functional properties.

Abstract This paper reviews the recent progress in the preparation of oxide-based and heteroatom-doped particles. Surfactant-templated oxide particles, e.g. silica and titania, are possible candidates for various potential applications such as adsorbents, photocatalysts, and optoelectronic and biological materials. We highlight nanoporous oxides of one element, such as silicon or titanium, and those containing multiple elements, which exhibit properties that are not achieved with individual components. Although the multicomponent nanoporous oxides possess a number of attractive functions, the origin of their properties is hard to determine due to compositional/structural complexity. Particles with a well-defined size and shape are keys for a quantitative and detailed discussion on the unique complex properties of the particles. From this viewpoint, we review the synthesis techniques of the oxide particles, which are functionalized with organic molecules or doped with heteroatoms, the physicochemical properties of the particles and the possibilities for their photofunctional applications as complex systems.

Effect of interfacial proteins on osteoblast-like cell adhesion to hydroxyapatite nanocrystals.

A quartz crystal microbalance with dissipation (QCM-D) technique was employed to detecting the protein adsorption and subsequent osteoblast-like cell adhesion to hydroxyapatite (HAp) nanocrystals. The interfacial phenomena with the preadsorption of three proteins (albumin (BSA), fibronectin (Fn), and collagen (Col)), the subsequent adsorption of fetal bovine serum (FBS), and the adhesion of the cells were investigated. The QCM-D measured the frequency shift (Δf) and dissipation energy shift (ΔD), and the viscoelastic properties of the adlayers were evaluated using ΔD-Δf plot and Voigt-based viscoelastic model. The Col adsorption significantly showed higher Δf, ΔD, elasticity, and viscosity values as compared to the BSA and Fn adsorption, and the subsequent FBS adsorption depended on the preadsorbed proteins. The ΔD-Δf plot of the cell adhesion also showed a different behavior depending on the surfaces, and the Fn- and Col-modified surfaces showed the rapid mass and ΔD changes by forming the viscous interfacial layers with cell adhesion, indicating that the processes were affected by the cellular reaction through the extracellular matrix (ECM) proteins. The confocal laser scanning microscope images of adherent cells showed a different morphology and pseudopod on the surfaces. The cells adhered to the surfaces modified with the Fn and Col had significantly uniaxially expanded shapes and fibrous pseudopods, and those modified with the BSA had a round shape. Therefore, the different cell-protein interactions would cause the arrangement of the ECM and the cytoskeleton changes at the interfaces, and these phenomena were successfully detected by the QCM-D and Voigt-based model.

Synthesis and luminescence properties of Eu(III)-doped nanoporous silica spheres.

Europium (III) (Eu(3+))-doped nanoporous silica spheres were synthesized, and the states of Eu(3+) ions in the silica framework structure were investigated. The ordered nanopores were preserved with the doping at the Eu(3+) molar concentration to Si up to 10 mol%, and the O-Si-O and Si-OH groups in the structures were clearly rearranged with the doping, indicating the interaction of Eu(3+) with the O atoms. The significant morphological changes in the spheres were observed with the doping. The photoluminescence spectral shapes due to the transitions of (5)D(0)-(7)F(1) and (5)D(0)-(7)F(2) were indicative of the presence of the Eu(3+) in an environment of a low symmetry. It was found that the Eu(3+) was located inside the silica framework to electrostatically interact with the environmental O atoms, which would prevent the aggregation among Eu(3+) ions to show the efficient luminescence. Therefore, the interactions between the Eu(3+) ions and silica framework structures in the spheres were successfully clarified.

Detection of Interfacial Phenomena with Osteoblast-like Cell Adhesion on Hydroxyapatite and Oxidized Polystyrene by the Quartz Crystal Microbalance with Dissipation

The adhesion process of osteoblast-like cells on hydroxyapatite (HAp) and oxidized polystyrene (PSox) was investigated using a quartz crystal microbalance with dissipation (QCM-D), confocal laser scanning microscope (CLSM), and atomic force microscope (AFM) techniques in order to clarify the interfacial phenomena between the surfaces and cells. The interfacial viscoelastic properties (shear viscosity (η(ad)), elastic shear modulus (μ(ad)), and tan δ) of the preadsorbed protein layer and the interface layer between the surfaces and cells were estimated using a Voigt-based viscoelastic model from the measured frequency (Δf) and dissipation shift (ΔD) curves. In the ΔD-Δf plots, the cell adhesion process on HAp was classified as (1) a mass increase only, (2) increases in both mass and ΔD, and (3) slight decreases in mass and ΔD. On PSox, only ΔD increases were observed, indicating that the adhesion behavior depended on the surface properties. The interfacial μ(ad) value between the material surfaces and cells increased with the number of adherent cells, whereas η(ad) and tanδ decreased slightly, irrespective of the surface. Thus, the interfacial layer changed the elasticity to viscosity with an increase in the number. The tan δ values on HAp were higher than those on PSox and exceeded 1.0. Furthermore, the pseudopod-like structures of the cells on HAp had periodic stripe patterns stained with a type I collagen antibody, whereas those on PSox had cell-membrane-like structures unstained with type I collagen. These results indicate that the interfacial layers on PSox and HAp exhibit elasticity and viscosity, respectively, indicating that the rearrangements of the extracellular matrix and cytoskeleton changes cause different cell-surface interactions. Therefore, the different cell adhesion process, interfacial viscoelasticity, and morphology depending on the surfaces were successfully monitored in situ and evaluated by the QCM-D technique combined with other techniques.

Reusable hydroxyapatite nanocrystal sensors for protein adsorption

Abstract The repeatability of the adsorption and removal of fibrinogen and fetal bovine serum on hydroxyapatite (HAp) nanocrystal sensors was investigated by Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance with dissipation (QCM-D) monitoring technique. The HAp nanocrystals were coated on a gold-coated quartz sensor by electrophoretic deposition. Proteins adsorbed on the HAp sensors were removed by (i) ammonia/hydrogen peroxide mixture (APM), (ii) ultraviolet light (UV), (iii) UV/APM, (iv) APM/UV and (v) sodium dodecyl sulfate (SDS) treatments. FTIR spectra of the reused surfaces revealed that the APM and SDS treatments left peptide fragments or the proteins adsorbed on the surfaces, whereas the other methods successfully removed the proteins. The QCM-D measurements indicated that in the removal treatments, fibrinogen was slowly adsorbed in the first cycle because of the change in surface wettability revealed by contact angle measurements. The SDS treatment was not effective in removing proteins. The APM or UV treatment decreased the frequency shifts for the reused HAp sensors. The UV/APM treatment did not induce the frequency shifts but decreased the dissipation shifts. Therefore, we conclude that the APM/UV treatment is the most useful method for reproducing protein adsorption behavior on HAp sensors.

Synthesis of luminescent nanoporous silica spheres functionalized with folic acid for targeting to cancer cells.

Luminescent europium(III)-doped nanoporous silica nanospheres (Eu:NPS) were successfully synthesized, and a folate N-hydroxysuccinimidyl ester (FA-NHS) molecule as a targeting ligand for cancer cells was immobilized on the nanosphere surfaces through mediation of the 3-aminopropyltriethoxysilane (APTES) adlayer. The ordered nanopores were preserved by the immobilization, and the specific surface area decreased only with the APTES immobilization, suggesting that the FA-NHS was predominantly immobilized on the outer surface of the nanopores. The photoluminescence of the nanospheres functionalized with folic acid (FA) exhibited a characteristic peak due to the interactions (e.g., energy transfer) between FA and Eu(3+), and further the orange luminescence could be clearly detected by fluorescence microscopy in air and water. Furthermore, the nanospheres highly dispersed in cell culture medium exhibited nontoxicity in the cellular proliferation stages of the Hela cancer cells and NIH3T3 fibroblasts and specifically bind to the Hela cells. The nanospheres after the binding and uptake also showed intense luminescence from the outer/inner cell surfaces for the culture time of 4 days. Therefore, the luminescent FA-functionalized Eu:NPS nanospheres could be used for specific targeting and imaging abilities for cancer cells.

Efficient incorporation of monomeric anthracene into nanoporous silica/surfactant nanocomposite spheres using a mechanochemical solid state reaction

The incorporation of anthracene (Ant) into nanoporous silica/surfactant nanocomposite spheres was successfully achieved using a mechanochemical solid state reaction. The Ant molecules were incorporated into the nanopores while preserving the silica nanostructures, indicating the effective hydrophobic interactions with the alkyl chains of the surfactant. The blue photoluminescence intensity due to the monomer state was enhanced by increasing the mechanochemical milling force, suggesting this is an efficient preparation method for a luminescent medium by monomeric assembly of the Ant molecules.

Ultrasound stimulus inducing change in hydrogen bonded crosslinking of aqueous polyvinyl alcohols

The effect of ultrasound (US) stimulation on the shear viscosity of aqueous polyvinyl alcohol (PVA) solution was studied when the solution was exposed to US at 23, 43, 96, and 141 kHz. The US stimulus showed a marked decrease of the shear viscosity of the solution in the order of 43>96>23>141 kHz, respectively, under US power dissipation of 8.5, 8.9, 8.9, and 8.8 W. Subsequently, when US exposure was stopped, the shear viscosity of PVA reverted to its original value. The US stimulation was analyzed with the US power transmitted through the PVA aqueous media. Furthermore, FT-IR spectra measured at different durations of US exposure, suggest that hydrogen bonds in the PVA segments were broken by the US exposure. We conclude that structural changes of the hydrogen bonded crosslinks of PVA were induced to include water molecules for the re-forming of crosslinks of aqueous PVA.

Immobilization of folic acid on Eu3+-doped nanoporous silica spheres.

Folic acid (FA) was immobilized on Eu(3+)-doped nanoporous silica spheres (Eu:NPSs) through mediation of the 3-aminopropyltriethoxysilane adlayer. The ordered nanopores of Eu:NPS were preserved by the immobilization. The FA-immobilized Eu:NPSs showed the characteristic photoluminescence peak due to interactions between the FA molecules and Eu(3+) ions, and highly dispersed stability in phosphate buffered saline.

Elemental distribution analysis of type I collagen fibrils in tilapia fish scale with energy-filtered transmission electron microscope

Elemental distribution of calcium, phosphorus, oxygen, and carbon in a single collagen fibril obtained from tilapia fish scales was identified with an electron energy-loss spectroscopy and an energy-filtered transmission electron microscopy, for the first time. The carbon intensity profile of the single collagen fibril showed the specific D-periodic pattern at 67 nm of type I collagen fibrils. The calcium L(2,3)-edge and oxygen K-edge peak positions were detected at 347/350 eV and 137 eV, respectively, and these positions were identical to those of hydroxyapatite. Calcium, phosphorus, and oxygen were present in the hole zones as the amorphous phase, while carbon was present in the overlap zone. Our results indicated that the hole zones preferentially attract calcium and phosphate ions and thus serve as possible nucleation sites for mineralization.