San-Yuan Chen

Quantum-Dot-Tagged Reduced Graphene Oxide Nanocomposites for Bright Fluorescence Bioimaging and Photothermal Therapy Monitored In Situ

Quantum-dot-tagged reduced graphene oxide (QD-rGO) nanocomposites (left) internalized into targeted tumor cells display bright fluorescence from the QDs (right); by absorbing NIR radiation incident on the rGO and converting it into heat, they also cause simultaneous cell death and fluorescence reduction (bottom). The nanocomposite is thus capable of tumor imaging, photothermal therapy and in situ monitoring of treatment in progress.

Controlled Rupture of Magnetic Polyelectrolyte Microcapsules for Drug Delivery

In this study, a magnetic-sensitive microcapsule was prepared using Fe 3O 4/poly(allylamine) (Fe 3O 4/PAH) polyelectrolyte to construct the shell. Structural integrity, microstructural evolution, and corresponding release behaviors of fluorescence dyes and doxorubicin were systematically investigated. Experimental observations showed that the presence of the magnetic nanoparticles in the shell structure allowed the shell structure to evolve from nanocavity development to final rupture of the shell under a given magnetic stimulus of different time durations. Such a microstructural evolution of the magnetic sensitive shell structure explained a corresponding variation of the drug release profile, from relatively slow release to burst-like behavior at different stages of stimulus. It has proposed that the presence of magnetic nanoparticles produced heat, due to magnetic energy dissipation (as Brown and Neel relaxations), and mechanical vibration and motion that induced stress development in the thin shell. Both mechanisms significantly accelerated the relaxation of the shell structure, causing such a microstructural evolution. With such a controllable microstructural evolution of the magnetic-sensitive shell structure, active substances can be well-regulated in a manageable manner with a designable profile according to the time duration under magnetic field. A cell culture study also indicated that the magnetic-sensitive microcapsules allowed a rapid uptake by the A549 cell line, a cancerous cell line, suggesting that the magnetic-sensitive microcapsule with controllable rupturing behavior of the shell offers a potential and effective drug carrier for anticancer applications.

Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films

A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical properties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transformed into single-phase rutile TiO2 at temperatures ⩾ 550 °C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 °C only. An increase in the oxidation temperatures ranging between 700 and 900 °C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (Eg). According to the coherent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen deficiency at a higher oxidation temperature rather than the presence of an amorphous component in the prepared films.

Properties of nitrogen-implanted p-type ZnO films grown on Si3N4/Si by radio-frequency magnetron sputtering

An nitrogen-implanted p-type ZnO film has been grown on a Si substrate buffered with Si3N4 using radio-frequency magnetron sputtering. The Si3N4 buffer layer can effectively improve film stoichiometry and reduce the formation of oxygen vacancies compared to ZnO on Si. The electrical properties of the p-type ZnO films implanted with 5×1012–1×1014 cm−2 N+ dose show a hole concentration of 5.0×1016–7.3×1017 cm−3, hole mobility of 2.51–6.02 cm2/V s, and resistivity of 10.11–15.3 Ω cm. The p-type ZnO films also showed an excellent crystallinity and a strong ultraviolet emission peak near 3.30 eV at room temperature. Moreover, as evidenced by extended x-ray absorption fine structure analysis, the local structure of the p-type ZnO films was changed due to the substitution of nitrogen ions for oxygen ions in p-type ZnO films. Our finding of p-type ZnO films grown on a Si3N4/Si substrate could provide a simple method to fabricate reproducible p-type ZnO films on silicon substrate for the development of large-scale...

Structural characterization of nano-sized calcium deficient apatite powders

Nano-sized calcium-deficient apatitic (CDHA) crystals with Ca/P ratios from 1.5 to 1.67 were synthesized using wet chemical method and of needle-like shape with 5-10 nm in diameter and 40-50 nm in length was observed. The structural environment of the Ca atoms in all the CDHA nano-crystals has been investigated using EXAFS, XANES and EELS. The results reveal that a maximum Fourier transform amplitude occurs at the apatite with a Ca/P ratio of 1.67 and the structural disorder increase following the sequence of 1.67>1.5>1.6>1.55. A similar phenomenon is also observed in both K-edge XANES and L(2,3)-edge ELNES in the Ca atom. The structural analysis further demonstrates that different chemical and biological properties among these CDHA nano-crystals with Ca/P ratio from 1.5 to 1.67 are primarily due to the effect of stoichiometry and non-stoichiometry as compared to the structural order-disorder.

Enhanced luminescent and electrical properties of hydrogen-plasma ZnO nanorods grown on wafer-scale flexible substrates

Photoelectronic characteristics are performed in well-aligned hydrogen-plasma ZnO nanorods grown on 4 in. flexible organic substrates buffered with ZnO film. Enhancement of photoluminescence (PL) properties due to H2 plasma treatment by a factor of 60 times for relative intensity ratio (ultraviolet emission to deep level emission) has been observed. X-ray photoelectron spectroscopy analysis reveals that the enhanced PL property is attributed to both defect passivation and modification on the surface region of ZnO nanorods due to the absorption of hydrogen ions. However, the PL spectra of H2 plasma ZnO nanorods can be restored to the original state of ZnO nanorods by thermal annealing process. The current-voltage measurements suggest that the n-type ZnO nanorods with H2 plasma treatment present a higher conductivity of about 5–6 orders of magnitude than the nonplasma ZnO nanorods.

Core/Single‐Crystal‐Shell Nanospheres for Controlled Drug Release via a Magnetically Triggered Rupturing Mechanism

Core/single-crystal-shell nanospheres are constructed from a poly-(N-vinyl- 2-pyrrolidone) (PVP)-modified silica core with an outer layer of single-crystal iron oxide shell. The nanospheres show outstanding release-and-zero-release characteristics via the addition and removal, respectively, of an external high-frequency magnetic field.

Core-shell CuInS2/ZnS quantum dots assembled on short ZnO nanowires with enhanced photo-conversion efficiency

A novel quantum-dot-based solar cell assembly consisting of core-shell Zn-doped CuInS2@ZnS (Zn-CIS@ZnS) quantum dots associated with short ZnO (5 μm in length) nanowires was developed and systematically investigated in terms of its nanostructure and optical properties, associated with corresponding solar cell parameters, i.e., VOC, JSC, fill factor (FF). In this investigation, the photo-conversion efficiency of the Zn-CIS-based solar cells without the presence of the ZnS shell can be readily tuned by controlling the Zn/Cu ratio. Furthermore, the efficiency was significantly improved upon the deposition of a thin ZnS shell on these Zn-CIS QDs, where a significant enhancement in short-circuit current density (JSC) by 88% was observed because the ZnS coating is able to effectively eliminate excited electron recombination and enhance the charge transfer efficiency from Zn-CIS QDs to ZnO nanowires. Power-conversion efficiency as high as 0.71% can be attained, which is improved more than 2–3 times compared with that without ZnS coating. Such a unique nanoarchitecture through coupling with both core-shell QDs and short ZnO nanowires suggests a promising design for a quantum dot-based solar cell with considerably improved power-conversion efficiency.

Multifunctional Nanocapsules for Simultaneous Encapsulation of Hydrophilic and Hydrophobic Compounds and On-Demand Release

Cocktail therapy by delivering multiple drugs to diseased cells can elicit synergistic therapeutic effects and better modulate the complex cell-signaling network. Besides selection of drug combinations, a difficulty in delivery is how to encapsulate drugs with various solubility into a common vehicle, particularly when both hydrophobic and hydrophilic compounds are involved. Furthermore, it is highly desirable that the drug release profile can be controlled in an on-demand fashion for balanced therapeutic and side effects. On the basis of a simple and scalable double emulsion approach, we report a new class of nanocapsules that can solve these problems simultaneously. Further linking the nanocapsules with peptides targeting cell surface integrins leads to significantly enhanced cell uptake of the nanocapsules. Intracellular drug release triggered by external stimuli has also been achieved without affecting cell viability. Further development of this technology should open exciting opportunities in treating tough diseases such as cancer, cardiovascular diseases, neurological disorders, and infectious diseases.

Synthesis and characterization of needlelike apatitic nanocomposite with controlled aspect ratios

Calcium-deficient apatitic (cd-HA) crystals with core-shell nanostructure with needlelike shape, 5-10nm in diameter and 20-80nm in length, were prepared via an in situ formation in the presence of polyacrylic acid (PAA) under aqueous solution of different pH values, ranging from 9 to 11. Nanostructure of the resulting crystals showing a core-shell configuration with a thin layer of PAA shell of about 1nm thickness was investigated. Aspect ratio (AR) of the needlelike composite was found to depend on the concentration of the PAA and solution pH. At lower solution pH, crystal growth was inhibited, i.e., leading to a decreased AR, with increase of PAA concentration, while an increased AR was detected at higher solution pH, suggesting a preferential growth of the cd-HA nanocrystals. Mechanism of such preferential growth was tentatively proposed and is suggested to correct PAA adsorption along the long axis of the needlelike nanoparticles.