Hyuksang Kwon

Full Surface Embedding of Gold Clusters on Silicon Nanowires for Efficient Capture and Photothermal Therapy of Circulating Tumor Cells

We report on rapid thermal chemical vapor deposition growth of silicon nanowires (Si NWs) that contain a high density of gold nanoclusters (Au NCs) with a uniform coverage over the entire length of the nanowire sidewalls. The Au NC-coated Si NWs with an antibody-coated surface obtain the unique capability to capture breast cancer cells at twice the highest efficiency currently achievable (~88% at 40 min cell incubation time) from a nanostructured substrate. We also found that irradiation of breast cancer cells captured on Au NC-coated Si NWs with a near-infrared light resulted in a high mortality rate of these cancer cells, raising a fine prospect for simultaneous capture and plasmonic photothermal therapy for circulating tumor cells.

Ultrathin and Flat Layer Black Phosphorus Fabricated by Reactive Oxygen and Water Rinse

Ultrathin black phosphorus (BP) is one of the promising two-dimensional (2D) materials for future optoelectronic devices. Its chemical instability in ambient conditions and lack of a bottom-up approach for its synthesis necessitate efficient etching methods that generate BP films of designed thickness with stable and high-quality surfaces. Herein, reporting a photochemical etching method, we demonstrate a controlled layer-by-layer thinning of thick BP films down to a few layers or a single layer and confirm their Raman and photoluminescence characteristics. Ozone molecules generated by O2 photolysis oxidize BP, forming P2O5-like oxides. When the resulting phosphorus oxides are removed by water, the surface of BP with preset thickness is highly flat and self-protective by surface oxygen functional groups. This method provides a fabrication strategy of BP and possibly other 2D semiconductors with band gaps tuned by their thickness.

Identification of CD23 as a functional receptor for the proinflammatory cytokine AIMP1/p43

Summary Aminoacyl-tRNA-synthetase-interacting multifunctional protein 1 (AIMP1/p43) can be secreted to trigger proinflammatory molecules while it is predominantly bound to a cytoplasmic macromolecular protein complex that contains several different aminoacyl-tRNA synthetases. Although its activities as a secreted signaling factor have been well characterized, the functional receptor for its proinflammatory activity has not yet identified. In this study, we have identified the receptor molecule for AIMP1 that mediates the secretion of TNF-&agr; from THP-1 monocytic cells and primary human peripheral blood mononuclear cells (PBMCs). In a screen of 499 soluble receptors we identified CD23, a known low-affinity receptor for IgE, as a high affinity binding partner of AIMP1. We found that downregulation of CD23 attenuated AIMP1-induced TNF-&agr; secretion and AIMP1 binding to THP-1 and PBMCs. We also observed that in THP-1 and PBMCs, AIMP1-induced TNF-&agr; secretion, mediated by CD23, involved activation of ERK1/2. Interestingly, endothelial monocyte activating polypeptide II (EMAP II), the C-terminal fragment of AIMP1 that is also known to work as a proinflammatory cytokine, was incapable of binding to CD23 and of activating ERK1/2. Therefore, identification of CD23 not only explains the inflammatory function of AIMP1 but also provides the first evidence by which the mode of action of AIMP1 can be distinguished from that of its C-terminal domain, EMAP II.

Stacking Structures of Few-Layer Graphene Revealed by Phase-Sensitive Infrared Nanoscopy

The stacking orders in few-layer graphene (FLG) strongly influences the electronic properties of the material. To explore the stacking-specific properties of FLG in detail, one needs powerful microscopy techniques that visualize stacking domains with sufficient spatial resolution. We demonstrate that infrared (IR) scattering scanning near-field optical microscopy (sSNOM) directly maps out the stacking domains of FLG with a nanometric resolution, based on the stacking-specific IR conductivities of FLG. The intensity and phase contrasts of sSNOM are compared with the sSNOM contrast model, which is based on the dipolar tip-sample coupling and the theoretical conductivity spectra of FLG, allowing a clear assignment of each FLG domain as Bernal, rhombohedral, or intermediate stacks for tri-, tetra-, and pentalayer graphene. The method offers 10-100 times better spatial resolution than the far-field Raman and infrared spectroscopic methods, yet it allows far more experimental flexibility than the scanning tunneling microscopy and electron microscopy.

Fabrication of surface plasmon-coupled si nanodots in au-embedded silicon oxide nanowires.

Adv. Mater. 2010, 22, 2421–2425 2010 WILEY-VCH Verlag G The bottom-up assembly of nanostructures on a dielectric matrix holds great promise for use in optoelectronic devices and photovoltaic solar cells because of the unique optical and electrical properties manifested only at the nanoscale. Notable examples include gold nanoparticle chains embedded in silicon oxide nanowires and crystalline Si (c-Si) nanodots embedded in a silicon oxide film. Recently, the simultaneous incorporation of both silicon and noble metal nanoparticles on a SiO2 matrix has become a particularly interesting issue because of the dramatic increase in light absorption, and emission of silicon-based materials related to the surface plasmon effect of the metal nanoparticles. Significant progress has been made on the synthesis of metal nanoparticles with various shapes and composition to control surface plasmonic properties. In our previous study, we reported a new fabrication method for size-controlled c-Si nanodots from a core–shell silicon oxide nanowire by electron-beam irradiation that leads to electron trapping followed by oxygen expulsion. In this paper, we aimed to fabricate a new noble metal–silicon hybrid nanowire with possible extraordinary optical properties by using a similar strategy as the one above to produce a high density of Si nanodots in gold-nanoparticle-embedded silicon oxide nanowires by electron-beam irradiation. We found that the formation mechanism of Si nanodots in this study is thermally driven, which is entirely different from earlier cases which resulted from electron trapping. Our method produces a high density (ca. 5.1 10 cm ) of amorphous Si (a-Si) and c-Si nanodots with a narrow size distribution. The optical characteristics of Si nanodots in the vicinity of the gold nanoparticles were investigated by monochromated electron energy-loss spectroscopy (EELS), which revealed a shift in the surface plasmon band of gold and a marked enhancement in the electron-induced excitation of Si nanodots. Furthermore, simple heat treatment at high temperature (1123K) yielded an unexpected Au/Si core–shell nanostructure with a corresponding shift in the plasmon band. We synthesized gold-nanoparticle-embedded silicon oxide nanowires by simply heating an n-type (100) silicon wafer onto which a thin (ca. 20 nm) gold layer had been deposited to 1273 K in a microchamber. The resulting nanowires were predominantly observed along the inner part of the downstream edge of the Si wafer. To understand how these hybrid nanowires came to be formed, we studied their structural evolution through detailed transmission electron microscopy (TEM) analyses, which revealed that gold silicide droplets that grow from the gold-coated substrate evolve into a gold peapod structure encapsulated in the silicon oxide nanowires (see Supporting Information, Fig. S1). A typical TEM image of the goldpeapod-embedded silicon oxide nanowire is shown in Figure 1a. The lattice-resolved TEM image (Fig. 1b) and its Fourier-transform diffractogram (Fig. 1b, inset) taken at the gold nanoparticle site unambiguously reveal the face centered cubic (fcc) structure of gold. On the other hand, both the high-resolution TEM (HRTEM) image (Fig. 1c) and the selective-area electron diffraction (SAED) pattern (Fig. 1d, inset) taken at the square-framed region in Figure 1a, together with its radial distribution function (RDF) (Fig. 1d), indicate that the nanowire matrix is in an amorphous phase, consisting of a short-range atomic arrangement similar to the monoclinic SiO2 structure. Figure 1e shows the energy-dispersive X-ray spectroscopy (EDS) data taken at the site marked by the red circle (A1) in Figure 1a, which reveals an approximate stoichiometry of SiO1.3 when compared against the EDS spectrum of our reference material, SiO2. In Figure 1f, the core-excitation electron energy-loss spectrum taken at A1 reveals a Si-L2,3 energy-loss near-edge structure (ELNES) of silicon-rich oxide (SRO), which is in accord with the EDS results. Electron-beam irradiation of these gold-peapod-embedded SRO nanowires yielded a high density of Si nanodots. Energy-filtered transmission electronmicroscopy (EF-TEM) gives the plasmon-loss images of Si filtered at 17 eV (Fig. 2a–c), which show that the number of Si nanodots formed between two gold particles increases with irradiation time. The bright zone in Figure 2b indicates the formation of a Si network following the initial nucleation of isolated clusters. As the irradiation proceeds further in time, Si atoms aggregate into nanodots in the amorphous SRO (a-SRO) matrix until eventually a high density of Si nanodots with a size of 4.0–5.5 nm are formed (Fig. 2c). If

Hot electrons at metal-organic interface: Time-resolved two-photon photoemission study of phenol on Ag(111)

We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the excitation mechanism and dynamical behavior of the anionic molecular resonance (MR) state of phenol weakly interacting with Ag(111). The photoexcited MR state of phenol was found at 3.1 eV above the Fermi level at 1 ML (monolayer) coverage, and the binding energy of this state remained rather constant at 0.74±0.05eV for all coverages. The polarization angle dependence of the 2PPE signal clearly showed that the MR state is populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the MR state was found to increase from 33 to 60 fs upon increasing the coverage from 1 to 9 ML, implying that the MR state becomes further decoupled from the bulk at a higher coverage. These results constitute the first time-resolved 2PPE study that clearly demonstrates the hot-electron-mediated mechanism operating for molecules that a...