Eue-Soon Jang

Hydrothermal route to ZnO nanocoral reefs and nanofibers

ZnO nanocoral reefs and nanofibers are synthesized on the glass substrate dip coated with ZnO seed with nanoparticles with an average size of 5 nm under a hydrothermal reaction. The ratios of length to diameter for the former and the latter are determined to be 100 and 1000, respectively. In addition, we found that a threshold power density for UV lasing action could be remarkably reduced from 40 kW/cm2 for the nanocoral reefs to 8 kW/cm2 for the nanofibers by increasing the cavity length of ZnO nanowires.

Whispering-gallery-modelike-enhanced emission from ZnO nanodisk

Hexagonal nanodisks of ZnO were fabricated by a solution process using ZnO nanoparticles and their cathodoluminescence characteristics were investigated. Monochromatic cathodoluminescence images showed that luminescence was spatially localized near the boundary of the nanodisk and spectral analysis in conjunction with the intensity profile consistently ascribed the spatial localization of luminescence to whispering-gallery-modelike-enhanced emission.

Cetuximab-conjugated magneto-fluorescent silica nanoparticles for in vivo colon cancer targeting and imaging

Magneto-fluorescent silica nanoparticles were conjugated with cetuximab for the targeting and imaging of colon cancer. In this study, cetuximab-conjugated magneto-fluorescent nanoparticles (MFSN-Ctx) could specifically target colon cancer cells that expressed EGFR on their cell membranes, and specific fluorescence was detected. MFSN-Ctx produced significant MRI signal changes in a human colon cancer xenograft mouse model. Intravenous injection of MFSN-Ctx resulted in faster uptake as compared to intraperitoneal injection, indicating that MFSN-Ctx had different kinetic properties in tumors based on the method of injection. The local concentration of MFSN-Ctx in a tumor was amplified by the use of an external magnetic field. These results demonstrate the potential application of MFSN-Ctx for the detection of EGFR-expressing colon cancer using in vivo imaging approaches.

Quantum confinement effect in ZnO∕Mg0.2Zn0.8O multishell nanorod heterostructures

We report on photoluminescence measurements of Mg0.2Zn0.8O∕ZnO∕Mg0.2Zn0.8O multishell layers on ZnO core nanorods. Dominant excitonic emissions in the photoluminescence spectra show a blueshift depending on the ZnO shell layer thickness attributed to the quantum confinement effect in the nanorod heterostructure radial direction. Furthermore, near-field scanning optical microscopy clearly shows sharp photoluminescence peaks from the individual nanorod quantum structures, corresponding to subband levels.

Intercalative route to heterostructured nanohybrids

Abstract We have successfully synthesized inorganic–inorganic, organic–inorganic and bio-inorganic nanohybrids by applying an intercalation technique systematically to layered titanate, molybdenum disulfide (MoS 2 ), Bi-based cuprate superconductors (Bi 2 Sr 2 Ca m −1 Cu m O y ( m =1, 2, and 3; BSCCO)), and to layered double hydroxides (LDHs), those which are of high importance in terms of basic understanding of intercalation reactions and of their practical applications. The inorganic–inorganic systems such as TiO 2 -pillared titanate, TiO 2 -pillared MoS 2 , and CdS–MoS 2 hybrids were synthesized by exfoliation–restacking method. A novel pillaring process using an osmotic swelling was developed to prepare TiO 2 -pillared layered titanate with a large surface area, high thermal stability, and enhanced photocatalytic activity. And the intercalation of TiO 2 and/or CdS nanocluster into the two dimensional MoS 2 lattice could be also realized by exfoliating and reassembling the lithiated molybdenum disulfide (LiMoS 2 ) in the presence of cationic TiO 2 and/or CdS nanocluster in an aqueous solution, respectively, to obtain the semiconductor–semiconductor hybrids. On the other hands, the organic–inorganic hybrids were achieved via intercalative complexation of iodine intercalated BSCOO with organic salt of Py–C n H 2 n +1 I (Py=pyridine). The high- T c superconducting intercalate with its remarkable lattice expansion can be applied as a precursor for superconducting colloids when dispersed in an appropriate solvent. This superconducting hybrid material had an unique structural feature of a superconducting-insulating-superconducting multilayer with atomically clean interfaces. Especially, this organic–inorganic nanohybrid is expected to be a promising precursor for preparing the superconducting colloidal suspension, which could be applied to the fabrication of superconducting films or wires. Recently, we were very successful in demonstrating in which the formation of bio-inorganic hybrids stabilized in the interlayer space of LDH retain their chemical and biological integrity. If necessary, LDH, as a reservoir, can be intentionally removed by dissolving it in an acidic media in such a way the interlayer biomolecules can be recovered or the intercalated biomolecules can be released from the LDH via ion-exchange reaction in electrolyte. It is, therefore, concluded that the inorganic LDH can play a role as a gene reservoir or carrier for various unstable organic or bio-molecules such as drugs and genes.

Soft-solution route to ZnO nanowall array with low threshold power density

ZnO nanowall array (ZNWA) has been directionally grown on the buffer layer of ZnO nanoparticles dip-coated on Si-wafer under a soft solution process. Nanowalls on substrate are in most suitable shape and orientation not only as an optical trap but also as an optical waveguide due to their unique growth habit, V[011¯0]⪢V[0001]≈V[0001¯]. Consequently, the stimulated emission at 384 nm through nanowalls is generated by the threshold power density of only 25 kW/cm2. Such UV lasing properties are superior to those of previously reported ZnO nanorod arrays. Moreover, there is no green (defect) emission due to the mild procedure to synthesize ZNWA.

The manipulation of natural killer cells to target tumor sites using magnetic nanoparticles.

The present work demonstrates that Cy5.5 conjugated Fe(3)O(4)/SiO(2) core/shell nanoparticles could allow us to control movement of human natural killer cells (NK-92MI) by an external magnetic field. Required concentration of the nanoparticles for the cell manipulation is as low as ~20 μg Fe/mL. However, the relative ratio of the nanoparticles loaded NK-92MI cells infiltrated into the target tumor site is enhanced by 17-fold by applying magnetic field and their killing activity is still maintained as same as the NK-92MI cells without the nanoparticles. This approach allows us to open alternative clinical treatment with reduced toxicity of the nanoparticles and enhanced infiltration of immunology to the target site.

Dynamic transition between Zn-HDS and ZnO; growth and dissolving mechanism of dumbbell-like ZnO bipod crystal

The dumbbell (DB) ZnO bipod crystal is directly grown from acetate anion intercalated Zn based hydroxyl double salts (Zn-HDS). Our results suggest that the (0001)-to-(0001) plane orientation of the DB ZnO crystal comes from the acetate anions intercalated into the Zn-HDS. The DB ZnO crystal is dynamically changed to tube, nanoplate, and the new Zn-HDS with interlayer spacing of 20.0A by etching the (000-1) surface.

Effect of magnetic field on reduction of magnetite

The reduction behaviour of magnetite oxide by hydrogen below Curie temperature was investigated in the presence of external magnetic field by thermogravimetric analysis. The reduction rate of magnetite powder increased with increasing external magnetic field strength below Curie temperature of magnetite. In order to figure out the effect of external magnetic field on reduction of magnetite, two types of magnetite, powder and pellet, were studied. It was possible to enhance the reduction rate of magnetite powder, because the particles of magnetite in the presence of an external magnetic field exposed more surface to the reducing gas. The effects of reduction temperature, reducing agent, iron oxide type, particle size and specimen shape on the metallisation behaviour of magnetite were visually clarified below the Curie temperature under the influence of external magnetic field. Despite of the increase in reduction degree by applied magnetic field, the rate controlling step was not changed due to the formation of porous metallic iron layer that keeps the path for reducing agent to approach the unreduced iron oxide in the core of magnetite particle.

Chimie douce route to hetero-structured high-Tc cuprates

Abstract Inorganic–inorganic and organic–inorganic hetero-structured high-Tc superconductors were achieved through a chimie douce (mild chemistry) route, in which inorganic or organic components were incorporated into the copper oxide superconductors, Bi2Sr2Cam−1CumOy (m=1, 2, and 3; BSCCO). According to the physico–chemical analyses for these nanohybrid materials, it is suggested that the high-Tc superconductivity is an intrinsic two-dimensional property of the copper oxide plane. All of these hetero-structured nanohybrid materials have an unique structural feature of a superconducting–insulating–superconducting (S–I–S) multilayer with atomically clean interfaces. Especially, the organic–inorganic nanohybrid is expected to be a promising precursor for superconducting colloidal suspension or nanoparticles, which could be applied to the fabrication of superconducting films or wires.