Takuya Tsuzuki

Human Skin Penetration of Sunscreen Nanoparticles: In-vitro Assessment of a Novel Micronized Zinc Oxide Formulation

The extent to which topically applied solid nanoparticles can penetrate the stratum corneum and access the underlying viable epidermis and the rest of the body is a great potential safety concern. Therefore, human epidermal penetration of a novel, transparent, nanoparticulate zinc oxide sunscreen formulation was determined using Franz-type diffusion cells, 24-hour exposure and an electron microscopy to verify the location of nanoparticles in exposed membranes. Less than 0.03% of the applied zinc content penetrated the epidermis (not significantly more than the zinc detected in receptor phase following application of a placebo formulation). No particles could be detected in the lower stratum corneum or viable epidermis by electron microscopy, suggesting that minimal nanoparticle penetration occurs through the human epidermis.

Reduced graphene oxide/ZnO composite: reusable adsorbent for pollutant management.

Reduced graphene oxide (RGO) coated with ZnO nanoparticles (NPs) was synthesized by a self-assembly and in situ photoreduction method, and then their application for removing organic pollutant from water was investigated. The RGO@ZnO composite nanomaterial has unique structural features including well-dispersed NPs on the surface and dense NPs loading. This composite exhibited a greatly improved Rhodamine B (RhB) adsorption capacity and an improved photocatalytic activity for degrading RhB compared to neat ZnO NPs. These properties made RGO@ZnO reusable for pollutant adsorbent. The composite showed an excellent cycling performance for organic pollutant removal up to 99% recovery over several cycles via simulated sunlight irradiation.

Nanopowders synthesized by Mechanochemical Processing

The activation of chemical reactions by milling reactants in a ball mill is presented here as a novel, low cost method for the synthesis of wide range of nanopowders with mean particle sizes as small as 4 nm. The factors controlling such mechanochemical reactions are discussed with respect to their influence on particle size, size distribution, and dispersion.

Immobilization of β-glucosidase on a magnetic nanoparticle improves thermostability: application in cellobiose hydrolysis.

The objective of the present work was to develop a thermostable β-glucosidase through immobilization on a nanoscale carrier for potential application in biofuel production. β-Glucosidase (BGL) from Aspergillus niger was immobilized to functionalized magnetic nanoparticles by covalent binding. Immobilized nanoparticles showed 93% immobilization binding. Immobilized and free BGL were characterized using Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) techniques. Free and immobilized enzyme exhibited different pH-optima at pH 4.0 and 6.0, respectively, but had the same temperature optima at 60 °C. Michaelis constant (KM) was 3.5 and 4.3mM for free and immobilized BGL. Thermal stability of the immobilized enzyme was enhanced at 70 °C. The immobilized nanoparticle-enzyme conjugate retained more than 50% enzyme activity up to the 16th cycle. Maximum glucose synthesis from cellobiose hydrolysis by immobilized BGL was achieved at 16 h.

Commercial scale production of inorganic nanoparticles

This review focuses on the current trend in the commercial scale production methods of inorganic nanoparticles. The limiting factors for the scalability of synthesis methods are explained and the relationship between commercial nanoparticle materials and production methods is discussed. Particular emphasis is placed on the fact that different synthesis techniques lead to different properties of nanoparticles even when the qualities such as particle size and crystal phase appear quite similar. The production techniques of nanoparticles need to be carefully selected based not only on the scalability and production costs, but also on the properties of nanoparticles required for specific applications.

Mechanochemical synthesis of nanocrystalline SnO2–ZnO photocatalysts

Mechanochemical processing of anhydrous chloride precursors with Na2CO3 has been investigated as a means of manufacturing nanocrystalline SnO2 doped ZnO photocatalysts. High-energy milling and heat-treatment of a 0.1SnCl2+0.9ZnCl2+Na2CO3+4NaCl reactant mixture was found to result in the formation of a composite powder consisting of oxide grains embedded within a matrix of NaCl. Subsequent washing with deionized water resulted in removal of the NaCl matrix phase and partial hydration of the oxide reaction product with the consequent formation of ZnSn(OH)6. The extent of this hydration reaction was found to decrease in a linear fashion with the temperature of the post-milling heat-treatment over the range of 400–700 °C. For a heat-treatment temperature of 700 °C, the SnO2 doped ZnO powder was found to exhibit significantly higher photocatalytic activity than either single-phase SnO2 or ZnO powders that were synthesized using similar processing conditions. The heightened photocatalytic activity of the SnO2 doped ZnO was attributed to its higher specific surface area and the enhanced charge separation arising from the coupling of ZnO with SnO2.

Reverse microemulsion-mediated synthesis of SiO2-coated ZnO composite nanoparticles : multiple cores with tunable shell thickness

Monodispersed SiO(2)-shell/ZnO-core composite nanospheres have been prepared in an oil-in-water microemulsion system. By using cyclohexane as the oil phase and Triton X-100 as the surfactant, composite nanospheres with high core loading levels and tunable shell thickness were obtained. Utilization of PVP capping agent on ZnO allowed the synthesis of composite nanospheres without forming any coreless SiO(2) spheres or shell-less ZnO particles. The photoactivity of ZnO nanoparticles was greatly reduced by SiO(2)-coating, which enables their applications as durable, safe, and nonreactive UV blockers in plastics, coating, and other products.

Structure and biodegradation mechanism of milled Bombyx mori silk particles.

The aim of this study was to understand the structure and biodegradation relationships of silk particles intended for targeted biomedical applications. Such a study is also useful in understanding structural remodelling of silk debris that may be generated from silk-based implants. Ultrafine silk particles were prepared using a combination of efficient wet-milling and spray-drying processes with no addition of chemicals other than those used in degumming. Milling reduced the intermolecular stacking forces within the β-sheet crystallites without changing the intramolecular binding energy. Because of the rough morphology and the ultrafine size of the particles, degradation of silk particles by protease XIV was increased by about 3-fold compared to silk fibers. Upon biodegradation, the thermal degradation temperature of silk increased, which was attributed to the formation of tight aggregates by the hydrolyzed residual macromolecules. A model of the biodegradation mechanism of silk particles was developed based on the experimental data. The model explains the process of disintegration of β-sheets, supported by quantitative secondary structural analysis and microscopic images.

Photoprotection by silk cocoons.

A silk cocoon protects a silkworm during its pupal stage from various threats. We systematically investigated the role of fiber, sericin, and embedded crystals in the UV protection of a silk cocoon. Diffuse reflectance and UV absorbance were measured and free radicals generated during exposure to UV radiation were quantified using photoinduced chemiluminescence (PICL). We identified the response to both UV-A and UV-B radiations by silk materials and found that sericin was primarily responsible for UV-A absorption. When sericin was removed, the photoinduced chemiluminescence intensity increased significantly, indicating higher UV-A-induced reactions of cocoons in the absence of sericin. There is progressively higher sericin content toward the outer part of the cocoon shell that allows an effective shield to pupae from UV radiation and resists photodegradation of silk fibers. The study will inspire development of advanced organic photoprotective materials and designing silk-based, free-radical-scavenging antioxidants.

Nanoparticle Coatings for UV Protective Textiles

TAs the intensity of ultraviolet (UV) radiation increases every year, effective methods to block UV rays to protect human skin, plastics, timber and other polymer materials are urgently sought. Textiles serve as important materials for UV protection in many applications. The utilisation of nanoparticles to textile materials has been the object of several studies aimed at producing finished fabrics with different performances. This article reviews the recent advancements in the field of UV blocking textiles and fibers that are functionalised with nanostructured surface coatings. Different types of UV blocking agents are discussed and various examples of UV blocking textiles that utilise zinc oxide (ZnO) and titanium dioxide (TiO2) are presented. Future challenges, such as wash-fastness and photocatalysis, are also discussed.