Jung-Hwan Hyung

Nanowire Substrate-based Laser Scanning Cytometry for Quantitation of Circulating Tumor Cells

We report on the development of a nanowire substrate-enabled laser scanning imaging cytometry for rare cell analysis in order to achieve quantitative, automated, and functional evaluation of circulating tumor cells. Immuno-functionalized nanowire arrays have been demonstrated as a superior material to capture rare cells from heterogeneous cell populations. The laser scanning cytometry method enables large-area, automated quantitation of captured cells and rapid evaluation of functional cellular parameters (e.g., size, shape, and signaling protein) at the single-cell level. This integrated platform was first tested for capture and quantitation of human lung carcinoma cells from a mixture of tumor cells and leukocytes. We further applied it to the analysis of rare tumor cells spiked in fresh human whole blood (several cells per mL) that emulate metastatic cancer patient blood and demonstrated the potential of this technology for analyzing circulating tumor cells in the clinical settings. Using a high-content image analysis algorithm, cellular morphometric parameters and fluorescence intensities can be rapidly quantitated in an automated, unbiased, and standardized manner. Together, this approach enables informative characterization of captured cells in situ and potentially allows for subclassification of circulating tumor cells, a key step toward the identification of true metastasis-initiating cells. Thus, this nanoenabled platform holds great potential for studying the biology of rare tumor cells and for differential diagnosis of cancer progression and metastasis.

A quartz nanopillar hemocytometer for high-yield separation and counting of CD4+ T lymphocytes

We report the development of a novel quartz nanopillar (QNP) array cell separation system capable of selectively capturing and isolating a single cell population including primary CD4(+) T lymphocytes from the whole pool of splenocytes. Integrated with a photolithographically patterned hemocytometer structure, the streptavidin (STR)-functionalized-QNP (STR-QNP) arrays allow for direct quantitation of captured cells using high content imaging. This technology exhibits an excellent separation yield (efficiency) of ~95.3 ± 1.1% for the CD4(+) T lymphocytes from the mouse splenocyte suspensions and good linear response for quantitating captured CD4(+) T-lymphoblasts, which is comparable to flow cytometry and outperforms any non-nanostructured surface capture techniques, i.e. cell panning. This nanopillar hemocytometer represents a simple, yet efficient cell capture and counting technology and may find immediate applications for diagnosis and immune monitoring in the point-of-care setting.

Ferromagnetic nickel silicide nanowires for isolating primary CD4+ T lymphocytes

Direct CD4+ T lymphocytes were separated from whole mouse splenocytes using 1-dimensional ferromagnetic nickel silicide nanowires (NiSi NWs). NiSi NWs were prepared by silver-assisted wet chemical etching of silicon and subsequent deposition and annealing of Ni. This method exhibits a separation efficiency of ∼93.5%, which is comparable to that of the state-of-the-art superparamagnetic bead-based cell capture (∼96.8%). Furthermore, this research shows potential for separation of other lymphocytes, B, natural killer and natural killer T cells, and even rare tumor cells simply by changing the biotin-conjugated antibodies.

ZnO Nanorod–TiO2-Nanoparticulate Electrode for Dye-Sensitized Solar Cells

Highly dense ZnO nanorods were synthesized on TiO2-nanoparticulate coated fluorine-doped tin oxide (FTO) substrates by the chemical vapor deposition method for dye-sensitized solar cells (DSSCs). The uniformly grown ZnO nanorod layer has a thickness of ~4 µm on the TiO2-nanoparticulate layer with a wurtzite structures as confirmed by the X-ray diffraction pattern. The DSSC fabricated with a ZnO nanorod/TiO2-nanoparticulate electrode had an overall light-to-electricity conversion efficiency η of 3.7% with a short-circuit current density JSC of 8.12 mA/cm2, open-circuit voltage VOC of 0.76 V, and fill factor FF of 0.59, whereas ZnO nanowire/TiO2-nanoparticulate-electrode-based DSSCs exhibited a low η of 1.1% with JSC of 2.14 mA/cm2 and slightly high VOC of 0.79 V. It is expected that the enhanced photovoltaic performance of the ZnO nanorod/TiO2-nanoparticulate electrode can be attributed to high dye loading and high light harvesting through large surface areas of ZnO nanorods incorporated with TiO2-nanoparticulate as compared with the ZnO nanowire/TiO2-nanoparticulate electrode.

The formation and characterization of electrical contacts (Schottky and Ohmic) on gallium nitride nanowires

We report on the fabrication and characterization of Ti/Au Ohmic contacts to unintentionally doped gallium nitride (n-GaN) nanowires. The specific contact resistance and resistivity were determined to be ~1.1 × 10−5 ± 5 × 10−6 Ω cm2 and ~6.9 × 10−3 ± 3 × 10−4 Ω cm, respectively, with a diameter of ~140 nm using a transmission line model (TLM). We also present the electrical characterizations of metal/GaN nano-Schottky diodes with four Schottky metals (Al, Ti, Cr and Au) on unintentionally doped GaN nanowires using current–voltage (I–V) characteristics at room temperature. We observed the abnormal electrical characteristics of GaN nano-Schottky diodes for each Schottky metal.

Direct observation of CD4 T cell morphologies and their cross-sectional traction force derivation on quartz nanopillar substrates using focused ion beam technique

Direct observations of the primary mouse CD4 T cell morphologies, e.g., cell adhesion and cell spreading by culturing CD4 T cells in a short period of incubation (e.g., 20 min) on streptavidin-functionalized quartz nanopillar arrays (QNPA) using a high-content scanning electron microscopy method were reported. Furthermore, we first demonstrated cross-sectional cell traction force distribution of surface-bound CD4 T cells on QNPA substrates by culturing the cells on top of the QNPA and further analysis in deflection of underlying QNPA via focused ion beam-assisted technique.

The size and diffusion effect of gold on silicon nanowire sidewall faceting

Single crystalline silicon nanowires (SiNWs) were grown using a gold (Au)-catalyzed vapor-liquid-solid (VLS) approach. In this study, we examine the influence of the size of Au catalyst droplets on the size of SiNWs and discuss the effect of Au diffusion and surface passivation on SiNW sidewall faceting and roughening in the VLS process. To simultaneously cover a variety of sizes of SiNWs on the same substrate, 2-nm-thick Au film was used on Si (111) substrate as a catalyst, since it is known that Au thin film–based seed offers relatively less control of the NW size, due to the randomness of the film breakup at reaction temperature. We then found that the grown SiNWs have two main types of surface morphologies on the sidewall of the nanowires (NWs). One type had a small and coarse surface morphology with no Au-Si droplets at the top of the NWs. The other type had a long and smooth surface and still had Au-Si droplets at the end. The fact that resulting SiNWs have two main different surface morphologies ca...

Dependence of Filopodia Morphology and the Separation Efficiency of Primary CD4+ T-Lymphocytes on Nanopillars

Despite significant improvement in separation efficiency using nanostructure-based platforms, the mechanism underlying the high efficiency of rare cell capture remains elusive. Here we report on the first mechanistic study by developing highly controlled nanostructures to investigate cell surface nanomorphology to better understand the cellular response of CD4(+) T-lymphocytes in contact with nanostructured surfaces and to elucidate key mechanisms for enhancing separation efficiency. Our results showed that actin-rich filopodia protruded from T-cells in the early stage of cell capture (<20 min), demonstrate the different morphologies in response to various quartz nanopillar (QNP) arrays functionalized with streptavidin and the generation of sufficient adhesion sites for rendering more stable binding through three-dimensional local nanotopographic interactions between filopodia-QNPs and cell-substrate, leading to synergistic effects for enhancing cell-capture efficiency. This responsive mechanism of T-cells on nanotopographic templates provides new insights to understand the enhanced cell-capture efficiency and specificity from the primary cell suspension on nanostructured substrates.

Effect of graphene oxide ratio on the cell adhesion and growth behavior on a graphene oxide-coated silicon substrate.

Control of living cells on biocompatible materials or on modified substrates is important for the development of bio-applications, including biosensors and implant biomaterials. The topography and hydrophobicity of substrates highly affect cell adhesion, growth, and cell growth kinetics, which is of great importance in bio-applications. Herein, we investigate the adhesion, growth, and morphology of cultured breast cancer cells on a silicon substrate, on which graphene oxides (GO) was partially formed. By minimizing the size and amount of the GO-containing solution and the further annealing process, GO-coated Si samples were prepared which partially covered the Si substrates. The coverage of GO on Si samples decreases upon annealing. The behaviors of cells cultured on two samples have been observed, i.e. partially GO-coated Si (P-GO) and annealed partially GO-coated Si (Annealed p-GO), with a different coverage of GO. Indeed, the spreading area covered by the cells and the number of cells for a given culture period in the incubator were highly dependent on the hydrophobicity and the presence of oxygenated groups on GO and Si substrates, suggesting hydrophobicity-driven cell growth. Thus, the presented method can be used to control the cell growth via an appropriate surface modification.

Long-term stability of Si-organic hybrid solar cells with a thermally tunable graphene oxide platform

We demonstrated that a reduced graphene oxide (rGO) layer inserted between a poly(3,4-etylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si interface improves the stability of Si-organic hybrid solar cells. Thermal reduction of a graphene oxide layer at different temperatures results in a change of water contact angle that is designed to eliminate the surface oxidation of the Si substrate. Higher temperatures generate a smaller aromatic sp2 domain size that changes the GO surface from hydrophilic to hydrophobic. Additionally, two-dimensional GO layers can serve as a barrier for both liquid and vapor permeation. Consequently, the PEDOT:PSS/Si device with a rGO passivation layer shows a significantly enhanced air-stability from the J–V characteristic under illumination during a one-month storage period. The application of rGO is a promising technique to extend the stability of Si-organic solar cells without an encapsulation process.