Polyglycerol Functionalized 10 B Enriched Boron Carbide Nanoparticle as an Effective Bimodal Anticancer Nanosensitizer for Boron Neutron Capture and Photothermal Therapies.

Boron neutron capture therapy (BNCT) is a non-invasive cancer treatment with little adverse effect utilizing nuclear fission of 10 B upon neutron irradiation. While neutron source has been developed from a nuclear reactor to a compact accelerator, only two kinds of drugs, boronophenylalanine and sodium borocaptate, have been clinically used for decades despite their low tumor specificity and/or retentivity. To overcome these challenges, various boron-containing nanomaterials, or "nanosensitizers", have been designed based on micelles, (bio)polymers and inorganic nanoparticles. Among them, inorganic nanoparticles such as boron carbide can include a much higher 10 B content, but successful in vivo applications are very limited. Additionally, recent reports on the photothermal effect of boron carbide are motivating for the addition of another modality of photothermal therapy. In this study, 10 B enriched boron carbide (10 B4 C) nanoparticle is functionalized with polyglycerol (PG), giving 10 B4 C-PG with enough dispersibility in a physiological environment. Pharmacokinetic experiments show that 10 B4 C-PG fulfills the following three requirements for BNCT; 1) low intrinsic toxicity, 2) 10 B in tumor/tumor tissue (wt/wt) ≥ 20 ppm, and 3) 10 B concentrations in tumor/blood ≥ 3. In vivo study reveals that neutron irradiation after intravenous administration of 10 B4 C-PG suppresses cancer growth significantly and eradicates cancer with the help of near-infrared light irradiation.

Fracture and Embedment Behavior of Brittle Submicrometer Spherical Particles Fabricated by Pulsed Laser Melting in Liquid Using a Scanning Electron Microscope Nanoindenter.

Generally, hard ceramic carbide particles, such as B4C and TiC, are angulated, and particle size control below the micrometer scale is difficult owing to their hardness. However, submicrometer particles (SMPs) with spherical shape can be experimentally fabricated, even for hard carbides, via instantaneous pulsed laser heating of raw particles dispersed in a liquid (pulsed laser melting in liquid). The spherical shape of the particles is important for mechanical applications as it can directly transfer the mechanical force without any loss from one side to the other. To evaluate the potential of such particles for mechanical applications, SMPs were compressed on various substrates using a diamond tip in a scanning electron microscope. The mechanical behaviors of SMPs were then examined from the obtained load-displacement curves. Particles were fractured on hard substrates, such as SiC, and fracture strength was estimated to be in the GPa range, which is larger than their corresponding bulk bending strength and is 10-40% of their ideal strength, as calculated using the density-functional theory. Contrarily, particles can be embedded into soft substrates, such as Si and Al, and the local hardness of the substrate can be estimated from the load-displacement curves as a nanoscale Brinell hardness measurement.

Behavior of Thermally Induced Nanobubbles during Instantaneous Particle Heating by Pulsed Laser Melting in Liquid.

Pulsed laser melting in liquid (PLML) is a technique to produce submicrometer spherical particles (SMPs). In this process, raw particles dispersed in liquid are selectively heated, and thermally induced nanobubbles (TINBs) at the particle surface are generated and act as a thermal barrier to enhance the temperature increase during heating. However, monitoring TINBs is difficult since PLML is a low-temperature, nonplasma process. Simple transmittance measurements of monodisperse Au SMP (250 nm) colloidal solutions on a transient time scale were used to monitor the temporal dependence of the TINB thickness and the pressure within the bubble. By applying this technique for ZnO and Sn SMP formation, TINBs in the PLML process are important in promoting the formation of large particles via particle merging during laser heating.

Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol.

Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse-1 cm-2 ) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000-4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML.

Slide-Ring Material/Highly Dispersed Graphene Oxide Composite with Mechanical Strength and Tunable Electrical Conduction as a Stretchable-Base Substrate.

The development of stretchable elastomer composites with considerable mechanical strength and electrical conductivity is desired for future applications in communication tools, healthcare, and robotics. Herein, we have developed a novel stretchable elastomer composite by employing a slide-ring (SR) material as a matrix for restoration and graphene oxide (GO) as a precursor for a conductive filler. Highly dispersed GO in an organic solvent, prepared via a new method developed by the authors, allowed the uniform dispersion of GO into the matrix by simply mixing the solvent and SR. The resultant SR/GO composite exhibited considerably high mechanical toughness and cyclic durability. These properties were approximately maintained after pulse laser irradiation to add electrical conductivity on the composite by photoreducing of the dispersed GO, and its electrical conductivity was higher than that of the SR/graphene, carbon nanotubes, or graphite composites. The potential of the SR/GO composite as a stretchable base substrate for wearable devices was demonstrated by producing a prototype humidity sensor, a human motion monitoring sensor, and an electrical heater based on the composite with conductive circuits drawn using pulse laser patterning.

Room-Temperature Laser Synthesis in Liquid of Oxide, Metal-Oxide Core-Shells, and Doped Oxide Nanoparticles.

Although oxide nanoparticles are ubiquitous in science and technology, a multitude of compositions, phases, structures, and doping levels exist, each one requiring a variety of conditions for their synthesis and modification. Besides, experimental procedures are frequently dominated by high temperatures or pressures and by chemical contaminants or waste. In recent years, laser synthesis of colloids emerged as a versatile approach to access a library of clean oxide nanoparticles relying on only four main strategies running at room temperature and ambient pressure: laser ablation in liquid, laser fragmentation in liquid, laser melting in liquid and laser defect-engineering in liquid. Here, established laser-based methodologies are reviewed through the presentation of a panorama of oxide nanoparticles which include pure oxidic phases, as well as unconventional structures like defective or doped oxides, non-equilibrium compounds, metal-oxide core-shells and other anisotropic morphologies. So far, these materials showed several useful properties that are discussed with special emphasis on catalytic, biomedical and optical application. Yet, given the endless number of mixed compounds accessible by the laser-assisted methodologies, there is still a lot of room to expand the library of nano-crystals and to refine the control over products as well as to improve the understanding of the whole process of nanoparticle formation. To that end, this review aims to identify the perspectives and unique opportunities of laser-based synthesis and processing of colloids for future studies of oxide nanomaterial-oriented sciences.

Hydrofluoric acid pretreatment effect on the formation of silicon submicrometer particles by pulsed laser melting in liquid and their optical scattering property.

Recently, the optical properties of silicon (Si) submicrometer spherical particles have been investigated to understand the dielectric nano-photonic function. Herein, we fabricated Si submicrometer spherical particles with high scattering efficiency using pulsed laser melting in deionized water or ethanol by irradiating laser at 66 mJ pulse-1 cm-2 via third harmonic of Nd:YAG laser. Hydrofluoric acid pretreatment was effective to remove surface oxide of raw Si particles; the laser fluence to obtain well crystallized spherical particles was lowered to 20 mJ pulse-1 cm-2 and the crystallinity of particles obtained were greatly improved without forming unwanted byproducts. The amount of particles was much more than those obtained by conventional fabrication technique. The particle size can be controlled by changing the laser fluence, and the scattering wavelength of colloidal solution can be controlled from visible to the near infrared range by increasing the laser fluence.

Determining the Composite Structure of Au-Fe-Based Submicrometre Spherical Particles Fabricated by Pulsed-Laser Melting in Liquid.

Submicrometre spherical particles made of Au and Fe can be fabricated by pulsed-laser melting in liquid (PLML) using a mixture of Au and iron oxide nanoparticles as the raw particles dispersed in ethanol, although the detailed formation mechanism has not yet been clarified. Using a 355 nm pulsed laser to avoid extreme temperature difference between two different raw particles during laser irradiation and an Fe2O3 raw nanoparticle colloidal solution as an iron source to promote the aggregation of Au and Fe2O3 nanoparticles, we performed intensive characterization of the products and clarified the formation mechanism of Au-Fe composite submicrometre spherical particles. Because of the above two measures (Fe2O3 raw nanoparticle and 355 nm pulsed laser), the products-whether the particles are phase-separated or homogeneous alloys-basically follow the phase diagram. In Fe-rich range, the phase-separated Au-core/Fe-shell particles were formed, because quenching induces an earlier solidification of the Fe-rich component as a result of cooling from the surrounding ethanol. If the particle size is small, the quenching rate becomes very rapid and particles were less phase-separated. For high Au contents exceeding 70% in weight, crystalline Au-rich alloys were formed without phase separation. Thus, this aggregation control is required to selectively form homogeneous or phase-separated larger submicrometre-sized particles by PLML.

Guided Slow Continuous Suspension Film Flow for Mass Production of Submicrometer Spherical Particles by Pulsed Laser Melting in Liquid.

Pulsed laser melting in liquid (PLML) is a technique to fabricate submicrometer crystalline spherical particles of various materials by laser irradiation of suspended raw particles with random shapes. To fully exploit the unique features of PLML-fabricated particles (crystalline and spherical) in practice, a mass-production PLML technique is required. To this end, the present study develops a new slit nozzle that guides the suspension film flow into a non-droplet continuous stream with a low flow rate. These two incompatible flow properties (continuity and slowness) are difficult to be realized for a liquid jet to free space. The suspension film flow was irradiated with a typical laboratory scale-flash lamp pumping laser at 30 Hz pulse frequency. Only a single flow passage of the slit nozzle with a few laser pulse irradiation transformed 95% of the raw particles into spherical particles. This spheroidizing ratio exceeded those of low-rate drip flow and high-rate cylindrical laminar flow directly jetted into free space through a Pasteur pipette nozzle. Extrapolating the data obtained from a 20-ml suspension, the average production rate was determined as 195 mg h-1. The high spheroidizing ratio and yield through the slit nozzle is attributable to the uniquely slow but continuous liquid film flow. The structure of the slit nozzle also prevents particles from adhering to the slit wall during continuous laser irradiation. Thus, the suspension film flow through the newly developed slit nozzle can potentially scale up the PLML technique to mass production.

Pulse-Width Dependence of the Cooling Effect on Sub-Micrometer ZnO Spherical Particle Formation by Pulsed-Laser Melting in a Liquid.

Sub-micrometer spherical particles can be synthesized by irradiating particles in a liquid with a pulsed laser (pulse width: 10 ns). In this method, all of the laser energy is supposed to be spent on particle heating because nanosecond heating is far faster than particle cooling. To study the cooling effect, sub-micrometer spherical particles are fabricated by using a pulsed laser with longer pulse widths (50 and 70 ns). From the increase in the laser-fluence threshold for sub-micrometer spherical particle formation with increasing pulse width, it is concluded that the particles dissipate heat to the surrounding liquid, even during several tens of nanoseconds of heating. A particle heating-cooling model considering the cooling effect is developed to estimate the particle temperature during laser irradiation. This model suggests that the liquid surrounding the particles evaporates, and the generated vapor films suppress heat dissipation from the particles, resulting in efficient heating and melting of the particles in the liquid. In the case of small particle sizes and large pulse widths, the particles dissipate heat to the liquid without forming such vapor films.

Laser-assisted one-pot fabrication of calcium phosphate-based submicrospheres with internally crystallized magnetite nanoparticles through chemical precipitation.

In this paper, we have further developed our simple (one-pot) and rapid (short irradiation time) laser fabrication process of submicrometer spheres composed of amorphous calcium iron phosphate. In our previous process, laser irradiation was applied to a calcium phosphate (CaP) reaction mixture supplemented with ferric ions (Fe(3+)) as a light-absorbing agent. Because the intention of the present study was to fabricate magnetite-encapsulated CaP-based submicrometer spheres, ferrous ions (Fe(2+)) were used as a light-absorbing agent rather than ferric ions. The ferrous ions served as a light-absorbing agent and facilitated the fabrication of submicrometer and micrometer spheres of amorphous calcium iron phosphate. The sphere formation and growth were better promoted by the use of ferrous ions as compared with the use of ferric ions. The chemical composition of the spheres was controllable through adjustment of the experimental conditions. By the addition of sodium hydroxide to the CaP reaction mixture supplemented with ferrous ions, fabrication of CaP-based magnetic submicrometer spheres was successfully achieved. Numerous magnetite and wüstite nanoparticles were coprecipitated or segregated into the CaP-based spherical amorphous matrix via light-material interaction during the CaP precipitation process. The magnetic properties of the magnetite and wüstite formed in the CaP-based spheres were investigated by magnetization measurements. The present process and the resulting CaP-based spheres are expected to have great potential for biomedical applications.

Preparation and investigation of the formation mechanism of submicron-sized spherical particles of gold using laser ablation and laser irradiation in liquids.

Results of very recent studies have shown that laser irradiation (LI) of colloidal nanoparticles (NPs) using a non-focused laser beam at moderate fluence transforms the NPs to submicron-sized spherical particles (SMPs). For this study, we applied this technique to prepare gold SMPs from source gold NPs prepared by laser ablation of a gold plate in an aqueous solution. Results show that SMPs were obtained from NPs in pure water, but a considerably large amount of the source NPs were sedimented without LI. On the other hand, SMPs were not obtained from NPs stabilized by 1 mM citrate. These findings indicate that the agglomeration of the source NPs prior to the laser-induced melting is important to obtain SMPs, although the sedimentation of the source NPs caused by considerable agglomeration should be reduced to obtain SMPs efficiently. A proper condition of the agglomeration tendency of the source NPs to prepare SMPs reducing the sedimentation of the source NPs was obtainable by simply adjusting the citrate solution concentration. Moreover, investigation of the temporal dynamics of the formation process of SMPs suggested that the agglomeration of the source NPs not only is controlled by citrate but also is induced by LI. LI brings about the decomposition and removal of citrate molecules on the surface of the source NPs, and cause the agglomeration of the source NPs dynamically; then it brings about the fusion of the agglomerated NPs.

Layered hydroxide nickel benzoates: hydrothermal synthesis, structure characterization, and exfoliation reaction.

This paper introduces two hydrothermally synthesized layered hydroxide nickel benzoates with the layered basic metal salt structures of basal spacings of 1.71 and 1.48 nm and their exfoliation reactions. These inorganic-organic hybrid layered compounds were characterized with XRD, FTIR, TG-DTA, SEM, SAED, and TEM. The 1.71 nm layered phase is a low temperature stable phase and has lattice parameters of a=0.7017(1)nm, b=0.3495(0)nm, c=1.763(7)nm, α=γ=90°, and ß=101.6(6)°. The 1.48 nm layered phase is a high temperature stable phase and has lattice parameters of a=0.6277(2)nm, b=0.3678(2)nm, c=1.514(1)nm, α=γ=90°, and ß=97.35(0)°. The benzoate anions in the interlayer space are coordinated to Ni(II) with unidentate and bidentate binding modes in the 1.71 nm layered phase, and with only bidentate binding mode in the 1.48 nm layered phase. These hybrid layered phases were exfoliated into their nanosheets in organic solvents, which gave a new category of inorganic-organic hybrid nanosheets. The exfoliation reactions are dependent on the structures and chemical compositions of the hybrid layered phases, as well as the molecule structures of the organic solvents used in the exfoliation.

Relationships between cell parameters of dye-sensitized solar cells and dye-adsorption parameters.

The performance of dye-sensitized solar cells (DSCs) is affected strongly by sensitizer-dye adsorption behavior on TiO(2) nanocrystal electrode. This study reports quantitative relationships between DSC cell performance parameters and dye-adsorption parameters for the first time. We discovered a logarithmic relationship between short-circuit photocurrent density (J(sc)) and dye-adsorption equilibrium constant on TiO(2) surface, and a linear relationship between open-circuit potential (V(oc)) and dye-adsorption density on TiO(2) surface for DSCs. These relationships provide a convenient method for forecasting the performance of TiO(2) nanoparticles for DSCs from the dye-adsorption parameters, and also indicate future directions for the development of high-performance TiO(2) nanoparticles for DSCs.

Single-crystalline rutile TiO2 hollow spheres: room-temperature synthesis, tailored visible-light-extinction, and effective scattering layer for quantum dot-sensitized solar cells.

A general synthesis of inorganic single-crystalline hollow spheres has been achieved through a mechanism analogous to the Kirkendall effect, based on a simple one-step laser process performed at room temperature. Taking TiO(2) as an example, we describe the laser process by investigating the influence of experimental parameters, for example, laser wavelength, laser fluence/irradiation time, liquid medium, and concentration of starting materials, on the formation of hollow spheres. It was found that the size-tailored TiO(2) hollow spheres demonstrate tunable light scattering over a wide visible-light range. Inspired by the effect of light scattering, we introduced the TiO(2) hollow sphere's scattering layer in quantum dot-sensitized solar cells and achieved a current notable 10% improvement of solar-to-electric conversion efficiency, indicating that TiO(2) hollow spheres are potential candidates in optical and optoelectronic devices.

Fabrication and characterization of core/shell structured TiO2/polyaniline nanocomposite.

A novel core/shell structured TiO(2)/polyaniline nanocomposite was fabricated by grafting aniline on aminobenzoate monolayer that is chemically adsorbed on the TiO(2) nanocrystal surface. The formation and nanostructure of the nanocomposite were investigated by FT-IR and UV-Vis spectra, TEM, FE-SEM, and TG-DTA analysis. Adsorption of aminobenzoate on the TiO(2) surface is an effective method to obtain the uniform nanocomposite. The thickness of polyaniline layer coating on the TiO(2) nanocrystal surface can be controlled in a range of 2-5 nm by this method. A photoelectrochemical study was carried out on the TiO(2)/polyaniline nanocomposite, and found that polyaniline in the nanocomposite acted as a visible-light sensitizer in a photoelectrochemical reaction. The sensitization effect increased with increasing binding strength between polyaniline and TiO(2). A dye-sensitized solar cell with a short circuit current density of 0.19 mA/cm(2) and an open circuit voltage of 0.35 V was fabricated by using the TiO(2)/polyaniline nanocomposite film as a sensitized electrode.

Submicron-sized boron carbide particles encapsulated in turbostratic graphite prepared by laser fragmentation in liquid medium.

Submicron-sized B4C spherical particles were obtained by laser fragmentation of large B4C particles dispersed in ethyl acetate. The irradiated surface of large B4C raw particles was heated and melted by laser energy absorption. B4C droplets were then cooled down, and finally B4C spherical particles were obtained. Moreover, each B4C particle obtained was encapsulated in a graphitic layer that is useful for medical functionalization of particles. Thus, obtained B4C particles encapsulated in graphitic layer may have potential uses in boron neutron capture therapy.

Preparation of zinc oxide nanorods using pulsed laser ablation in water media at high temperature.

ZnO columnar single crystals were formed by pulsed laser ablation in deionized water and surfactant aqueous solutions of lauryl dimethylaminoacetic acid (LDA) and cetyltrimethylammonium bromide (CTAB) at 80 degrees C. ZnO particles produced by laser ablation were dissolved at a higher temperature than 60 degrees C, and then crystalline growth to columnar structure proceeded. While large ZnO columnar crystals were obtained in deionized water, the crystals prepared in surfactant solution were smaller than those in deionized water due to inhibition of crystalline growth by surfactant adsorption on ZnO surfaces. The size of ZnO nanorods depended on how surfactant molecules adsorb on ZnO surface.

Surface treatment of silicon carbide using TiO2(IV) photocatalyst.

Silicon carbide (SiC) and diamond were decomposed to CO(2)(g) by the photocatalysis with TiO(2) at room temperature, although the decomposition rate of diamond was very slow. According to the XPS spectra of Si2p on the SiC surface, SiO(2) was simultaneously formed on the surface by the TiO(2) photocatalysis. The thickness of the SiO(2) formed on the SiC surface during the photocatalytic oxidation for 1 h was estimated to be about 40 A from the depth profile of the XPS spectra using Ar etching. The SiC surface was oxidized by the TiO(2) photocatalysis even under the condition without a direct contact with the TiO(2). This indicates that the photocatalytic oxidation of the SiC occurs due to active oxygen species photogenerated on the TiO(2) surface, but not by hole produced in the valence band of the TiO(2). Moreover, a remote surface treatment system using the quartz beads coated with TiO(2) was developed for the SiC surface oxidation. Consequently, the TiO(2) photocatalysis will be very useful for the surface treatment of SiC such as photopatterning without defects and damage to the substrate because the photocatalytic reaction is carried out under mild conditions.