Kyung-Hwa Yoo

Multifunctional Nanoparticles for Combined Doxorubicin and Photothermal Treatments

To facilitate combined doxorubicin and photothermal treatments, we developed doxorubicin-loaded poly(lactic-co-glycolic acid)-gold half-shell nanoparticles (DOX-loaded PLGA-Au H-S NPs) by depositing Au films on DOX-loaded PLGA NPs. As the PLGA NPs biodegraded, DOX was released, and heat was locally generated upon near-infrared (NIR) irradiation due to NIR resonance of DOX-loaded PLGA H-S NPs. Compared with chemotherapy or photothermal treatment alone, the combined treatment demonstrated a synergistic effect, resulting in higher therapeutic efficacy and shorter treatment times. Since our NPs selectively deliver both heat and drug to tumorigenic regions, they may improve the therapeutic effectiveness with minimal side effects.

Synergistic Cancer Therapeutic Effects of Locally Delivered Drug and Heat Using Multifunctional Nanoparticles

www.MaterialsViews.com C O M M U Synergistic Cancer Therapeutic Effects of Locally Delivered Drug and Heat Using Multifunctional Nanoparticles N IC A By Sun-Mi Lee , Huiyul Park , and Kyung-Hwa Yoo * IO N Near-infrared (NIR) light of 650 ∼ 900 nm is applicable for in vivo imaging and therapy due to minimal optical absorption by intrinsic chromophores, such as hemoglobin ( < 650 nm) and water ( > 900 nm), resulting in maximal penetration of light into biological tissues. [ 1 ] Therefore, various NIR resonant nanomaterials such as gold (Au) nanoshell particles, [ 2 , 3 ] Au nanocages, [ 4 , 5 ]

Organic photovoltaic devices with Ga-doped ZnO electrode

The authors report two organic photovoltaic devices using a Ga-doped ZnO (GZO) film as a transparent conducting electrode. In the first structure, the conventional In2O3:Sn hole-collecting anode was replaced by GZO and an efficiency of 0.35% was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4%. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere.

Humidity effects on the conductance of the assembly of DNA molecules

Abstract We have studied the effects of relative humidity on the conductance of the assembly of poly(dG)–poly(dC) and poly(dA)–poly(dT) DNA molecules. The exponential dependence of conductance on the relative humidity is observed and explained in terms of ionic conduction through the hydration layers around DNA. The poly(dG)–poly(dC) specimen has larger sensitivity to the relative humidity and smaller activation energy for the ionic conduction than the poly(dA)–poly(dT) specimen. Our results show that the conductance of a specimen consisting of multiple DNA molecules might be strongly affected by the relative humidity.

Electrically refreshable carbon-nanotube-based gas sensors

We report electrically refreshable carbon-nanotube (CNT)-based gas sensors with a field effect transistor (FET) structure. The sensors can be refreshed by applying a negative gate voltage pulse in NO2 and a positive gate voltage pulse in NH3. Furthermore, the temporal response of the conductance to the gate voltage pulse is observed to be dependent on the gas species, but independent of gas concentration. These results show the possibility of distinguishing gas species using CNT-FET sensors.

Fano resonance in crossed carbon nanotubes

We report the observation of the resonant transport in multiwall carbon nanotubes in a crossed geometry. The resonant transport is manifested by an asymmetric peak in the differential conductance curve. The observed asymmetric conductance peak is well explained by the Fano resonance originating from the scattering at the contact region of the two nanotubes. The conductance peak depends sensitively on the external magnetic field and exhibits Aharonov-Bohm-type oscillation.

Buffer layer effect on the structural and electrical properties of rubrene-based organic thin-film transistors

The structural and electrical properties of organic thin-film transistors with rubrene/pentacene and pentacene/rubrene bilayered structures were investigated using x-ray diffraction, atomic force microscopy, and x-ray emission spectroscopy. High-quality rubrene thin films with orthorhombic structure were obtained in the rubrene/pentacene bilayer while the pentacene/rubrene bilayer only had an amorphous rubrene phase present. The rubrene/pentacene thin-film transistor shows more desirable current-voltage characteristics compared to the pentacene/rubrene transistor. The overall results suggest that the presence of a chemically active organic buffer layer and its associated crystal structure are crucial in enhancing the structural and electrical properties of rubrene-based transistors.

Surface plasmon enhanced photoconductance and single electron effects in mesoporous titania nanofibers loaded with gold nanoparticles

We have synthesized mesoporous TiO2 nanofibers loaded with Au nanoparticles (MTNF-Au) and fabricated single nanofiber-based devices. MTNF-Au devices exhibited surface plasmon enhanced photoconductance under visible light, whereas MTNF devices without Au nanoparticles did not. Moreover, Coulomb oscillations were observed at 4.2 K in MTNF-Au devices, indicating that Au nanoparticles embedded in MTNF-Au played a role of Coulomb islands. These results suggested that the enhanced photoconductance was ascribed to electron tunneling of hot electrons generated by the surface plasmon resonance.

Distinguishing between apoptosis and necrosis using a capacitance sensor

Apoptosis and necrosis are two different paths for cell death. One of differences between apoptosis and necrosis is the cell morphology. Apoptotic cells shrink without loosing the integrity of their plasma membrane and break into smaller pieces called apoptotic bodies that other body cells recognize and eat. In contrast, necrotic cells swell and their plasma membrane eventually ruptures. Since the cell membrane is closely related to the capacitance (or dielectric constant), we have fabricated a capacitance sensor, which can measure the capacitance of cells, and investigated its time dependence during apoptosis and necrosis for TE2 cells induced by TNF-related apoptosis inducing ligand (TRAIL) and ethanol. The capacitance decreases monotonically during apoptosis. For necrosis, however, step-like behaviors are observed and dips are found in the dC/dt-t curves. The time-lapse images of TE2 cells, which have been taken simultaneously with the capacitance measurements, show that the dips in the dC/dt-t curves are probably due to the rupture of cell membrane. These results suggest that apoptosis and necrosis are differentiated by the capacitance measurements.

Ambipolar organic thin-film transistors using C60/pentacene structure: Characterization of electronic structure and device property

We fabricated ambipolar organic thin-film transistors (OTFTs) using C60 and pentacene. The electronic structure of the interface was investigated by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitude of the interface dipole and the band bendings at the interface was determined, and the complete energy level diagram for C60 on pentacene (C60/pentacene) was obtained. The lowered band offsets, due to the enhanced charge redistribution in C60/pentacene relative to pentacene on C60, are favorable for the ambipolar OTFTs. The measured field-effect mobilities were 0.017cm2∕Vs and 0.007cm2∕Vs for the p-channel and the n-channel operations, respectively. The threshold voltages were −2V for the p channel and 15.6V for the n channel, comparable to those of unipolar OTFTs using C60 or pentacene.