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.

Filopodial morphology correlates to the capture efficiency of primary T-cells on nanohole arrays.

Nanostructured surfaces emerge as a new class of material for capture and separation of cell populations including primary immune cells and disseminating rare tumor cells, but the underlying mechanism remains elusive. Although it has been speculated that nanoscale topological structures on cell surface are involved in the cell capture process, there are no studies that systematically analyze the relation between cell surface structures and the capture efficiency. Here we report on the first mechanistic study by quantifying the morphological parameters of cell surface nanoprotrusions, including filopodia, lamellipodia, and microvilli in the early stage of cell capture (< 20 min) in correlation to the efficiency of separating primary T lymphocytes. This was conducted by using a set of nanohole arrays (NHAs) with varying hole and pitch sizes. Our results showed that the formation of filopodia (e.g., width of filopodia and the average number of the filopodial filaments per cell) depends on the feature size of the nanostructures and the cell separation efficiency is strongly correlated to the number of filopodial fibers, suggesting a possible role of early stage mechanosensing and cell spreading in determining the efficiency of cell capture. In contrast, the length of filopodial filaments was less significantly correlated to the cell capture efficiency and the nanostructure dimensions of the NHAs. This is the first mechanistic study on nanostructure-based immune cell capture and provides new insights to not only the biology of cell-nanomaterial interaction but also the design of new rare cell capture technologies with improved efficiency and specificity.

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.

Electrical transport characterization of PEDOT:PSS/n-Si Schottky diodes and their applications in solar cells.

We demonstrate locally contacted PEDOT:PSS Schottky diodes with excellent rectifying behavior, fabricated on n-type Si substrates using a spin-coating process and a reactive-ion etching process. Electrical transport characterizations of these Schottky diodes were investigated by both current-voltage (I-V) and capacitance-voltage (C-V) measurements. We found that these devices exhibit excellent modulation in the current with an on/off ratio of - 10(6). Schottky junction solar cells composed of PEDOT:PSS and n-Si structures were also examined. From the current density-voltage (J-V) measurement of a solar cell under illumination, the short circuit current (I(sc)), open circuit voltage (V(oc)), and conversion efficiency (eta) were - 19.7 mA/cm2, - 578.5 mV, and - 6.5%, respectively. The simple and low-cost fabrication process of the PEDOT:PSS/n-Si Schottky junctions makes them a promising candidate for further high performance solar cell applications.

Reduction in thermal conductivity of Bi thin films with high-density ordered nanoscopic pores.

We prepared two-dimensional Bi thin films with high-density ordered nanoscopic pores by e-beam evaporation of Bi metal. For this structure, we used polystyrene beads ranging from 200 to 750 nm in diameter as an etch mask. The typical hole and neck sizes of the Bi thin films with approximately 50 nm in thickness on SiO2/Si substrates were in the range of 135 to 490 nm and 65 to 260 nm, respectively. By measuring the thermal characteristics through a 3ω technique, we found that the thermal conductivities of nanoporous Bi thin films are greatly suppressed compared with those of corresponding bulk materials. With a decrease in pore size to approximately 135 nm, the thermal conductivity decreased significantly to approximately 0.46 W/m·K at 300 K.

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.

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.

Effect of surface passivation on dielectrophoresis-prepared multi-channel ZnO nanowire field effect transistor (FETs).

We report on the effect of surface passivation on the electrical characteristics of multi-channel ZnO nanowire field-effect transistors (FETs). Surface passivation was performed using a SiO2 layer on ZnO nanowires. Multi-channel FETs were prepared by assembling as synthesized ZnO nanowires on a SiO2/Si substrate using an alternating current (AC) dielectrophoresis (DEP) technique. We observed that surface passivation with a SiO2 layer on ZnO nanowires was significantly affected by electrical characteristics of multi-channel ZnO nanowire FETs such as the threshold voltage and transconductance.

Thermally grown ZnO nanosheets for high efficiency dye-sensitized solar cells.

High efficiency dye-sensitized solar cells (DSSCs) were fabricated using ZnO nanosheet electrodes. ZnO nanosheets were synthesized on top of fluorine-doped tin oxide (FTO) glass using Zn(OAc)2 as a precursor in the gold catalyzed chemical vapor deposition (CVD) method at a temperature of 800-900 degrees C. The synthesized materials were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and Raman and photoluminescence (PL) spectroscopy. Typical DSSCs with ZnO nanosheets achieved moderately good conversion efficiency eta of approximately 2.12% with short-circuit current density J(SC) = 3.56 mA/cm2, open-circuit voltage V(OC) = 0.831 V, and fill factor FF = 71%. The high J(SC) and eta are attributed to high dye absorption through high surface ZnO nanosheets, which increased the light harvesting. The lower recombination rate was also observed in the ZnO nanosheet electrodes, resulting in high values of V(OC) and FF in the DSSCs.

AC dielectrophoresis alignment of ZnO nanowires and subsequent use in field-effect transistors.

We report on the dielectrophoresis (DEP) characterization of single crystalline zinc oxide (ZnO) nanowires with variations of the AC electric field and frequency. The alignment yield rate of ZnO nanowires in the gap over the 200 metal electrodes increased with increasing AC electric field and also changed by the applying frequency. Moreover, we demonstrated that the DEP prepared multi-ZnO nanowires field-effect transistors (FETs) exhibited excellent performance with a transconductance of approximately 3 muS and a high drain current of approximately 2.7 x 10(-6) A (V(DS) = 5 V, V(G) = 20 V).

Synthesis of single-crystalline ZnO nanowires and their applications in dye-sensitized solar cells (DSSCs) with a solid polyethylene glycol (PEG) redox electrolyte.

We demonstrate for the first time ZnO nanowire dye-sensitized solar cells (DSSCs) with a solid-state poly (ethylene glycol) (PEG) redox electrolyte. From the current-voltage characteristics of this solid PEG electrolyte-based ZnO nanowire DSSCs, the open-circuit voltage and short-circuit current density, and fill factor were determined to be approximately 0.58 V, approximately 1.30 mA/cm2, and 0.31, respectively. We obtained a power conversion efficiency of approximately 0.24% under an incident irradiation of 100 mW/cm2, corresponding to air mass (AM) 1.5 global solar conditions. The solid-state DSSC experienced an efficiency that was approximately 0.1% lower than the efficiency a liquid electrolyte based ZnO nanowire DSSC.