Chang Kyoung Choi

Wettability changes of TiO2 nanotube surfaces.

This study examines the effect of environmental and experimental conditions, such as temperature and time, on the wettability properties of titania nanotube (TNT) surfaces fabricated by anodization. The fabricated TNTs are 60-130 nm inner diameter and 7-10 µm height. One-microliter water droplets were used to define the wettability of the TNT surfaces by measuring the contact angles. A digital image analysis algorithm was developed to obtain contact angles, contact radii and center heights of the droplets on the TNT surfaces. Bare titanium foil is inherently less hydrophilic with approximately 60°-80° contact angle. The as-anodized TNT surfaces are more hydrophilic and annealing further increases this hydrophilic property. Furthermore, it was found that the TNT surface became more hydrophobic when aged in air over a period of three months. It is believed that the surface wettability can be changed due to alkane contamination and organic contaminants in an ambient atmosphere. This work can provide guidelines to better specify the environmental conditions that changes surface properties of TNT surfaces and therefore affect their desirable function in specific applications such as orthopedic implants.

ESE-1/EGR-1 Pathway Plays a Role in Tolfenamic Acid-induced Apoptosis in Colorectal Cancer Cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to prevent colorectal tumorigenesis. Although antitumor effects of NSAIDs are mainly due to inhibition of cyclooxygenase activity, there is increasing evidence that cyclooxygenase-independent mechanisms may also play an important role. The early growth response-1 (EGR-1) gene is a member of the immediate-early gene family and has been identified as a tumor suppressor gene. Tolfenamic acid is a NSAID that exhibits anticancer activity in a pancreatic cancer model. In the present study, we investigated the anticancer activity of tolfenamic acid in human colorectal cancer cells. Tolfenamic acid treatment inhibited cell growth and induced apoptosis as measured by caspase activity and bioelectric impedance. Tolfenamic acid induced EGR-1 expression at the transcription level, and analysis of the EGR-1 promoter showed that a putative ETS-binding site, located at −400 and −394 bp, was required for activation by tolfenamic acid. The electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirmed that this sequence specifically bound to the ETS family protein epithelial-specific ETS-1 (ESE-1) transcription factor. Tolfenamic acid also facilitated translocation of endogenous and exogenous ESE-1 to the nucleus in colorectal cancer cells, and gene silencing using ESE-1 small interfering RNA attenuated tolfenamic acid-induced EGR-1 expression and apoptosis. Overexpression of EGR-1 increased apoptosis and decreased bioelectrical impedance, and silencing of endogenous EGR-1 prevented tolfenamic acid-induced apoptosis. These results show that activation of ESE-1 via enhanced nuclear translocation mediates tolfenamic acid-induced EGR-1 expression, which plays a critical role in the activation of apoptosis. [Mol Cancer Ther 2008;7(12):3739–50]

Temperature measurement for a nanoparticle suspension by detecting the Brownian motion using optical serial sectioning microscopy (OSSM)

A concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of optical serial sectioning microscopy (OSSM). This technique measures optically diffracted particle images, the so-called point spread function (PSF), and determines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. A dry objective lens (40×, 0.75 NA) is used to detect the diffraction patterns of 500 nm polystyrene fluorescent (505/515) nanoparticles suspended in water at a volume concentration of 4 × 10−6, for a range of temperatures from 5 to 70 °C. The measured mean square displacement (MSD) data (figure 8, table 1) agree fairly well with the well-known Einstein predictions. Differentials of 5.54%, 4.26% and 3.19% were found for the 1D, 2D and 3D cases, respectively. In summary, the line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids.

Opto-Electric Cellular Biosensor Using Optically Transparent Indium Tin Oxide (ITO) Electrodes

Indium tin oxide (ITO) biosensors are used to perform simultaneous optical and electrical measurements in order to examine the dynamic cellular attachment, spreading, and proliferation of endothelial cells (ECs) as well as cytotoxic effects when exposed to cytochalasin D. A detailed description of the fabrication of these sensors is provided and their superior optical characteristics are qualitatively shown using four different microscopic images. Differential interference contrast microscopy (DICM) images were acquired simultaneously with micro-impedance measurements as a function of frequency and time. A digital image processing algorithm quantified the cell-covered electrode area as a function of time. In addition, cytotoxicity effects, produced by the toxic agent cytochalasin D, were examined using micro-impedance measurements, confocal microscopy images of stained actin-filaments, and interference reflection contrast microscopy (IRCM) capable of examining the bottom morphology of a cell. The results of this study show (1) the dynamic optical and electrical cellular characteristics using optically thin ITO biosensors; (2) qualitative agreement between cell-covered electrode area and electrical impedance during cellular attachment; (3) in vitro cytotoxicity detection of ECs due to 3 μM cytochalasin D. The present opto-electric biosensor system is unique in that a simultaneous and integrated cellular analysis is possible for a variety of living cells.

The evaporation and wetting dynamics of sessile water droplets on submicron-scale patterned silicon hydrophobic surfaces

The evaporation characteristics of 1 µl sessile water droplets on hydrophobic surfaces are experimentally examined. The proposed hydrophobic surfaces are composed of submicron diameter and 4.2 µm height silicon post arrays. A digital image analysis algorithm was developed to obtain time-dependent contact angles, contact diameters, and center heights for both non-patterned polydimethylsiloxane (PDMS) surfaces and patterned post array surfaces, which have the same hydrophobic contact angles. While the contact angles exhibit three distinct stages during evaporation in the non-patterned surface case, those in the patterned silicon post array surface case decrease linearly. In the case of post array hydrophobic surfaces, the initial contact diameter remains unchanged until the portion of the droplet above the posts completely dries out. The edge shrinking velocity of the droplet shows nonlinear characteristics, and the velocity magnitude increases rapidly near the last stage of evaporation.

Electrical impedance measurements predict cellular transformation.

Cellular transformation is the first step in cancer development. Two features of cellular transformation are proliferation in reduced serum and loss of contact inhibition. Electronic Cell‐Substrate Impedance Sensing (ECIS) measurements have been used to measure cellular proliferation, cytotoxicity, apoptosis, and attachment. We have used impedance measurements to distinguish normal cells from cells transformed with a constitutively active chemokine receptor, CXCR2. CXCR2, a member of the G‐protein coupled receptor (GPCR) family, is normally involved in cellular activation and migration, but a single amino acid substitution leads to constitutive activity. NIH3T3 cells were transformed with a constitutively active CXCR2 (D143V_CXCR2) and growth in reduced serum and foci formation were measured using established biological assays and compared to data from ECIS. The results of this study show that impedance measurements provide a quick and reliable way of measuring cellular transformation and provide real time assessment of transformed cellular parameters. Use of the ECIS system could allow a rapid screening of anti‐cancer drugs that alter cellular transformation.

Examination of near-wall hindered Brownian diffusion of nanoparticles: Experimental comparison to theories by Brenner (1961) and Goldman et al. (1967)

Multilayered distributions of hindered mean square displacement (MSD) for nanoparticles are measured in the near-wall region within 500 nm from the solid surface using total internal reflection fluorescence microscopy, an evanescent wave microscopic imaging technique. Examined particles are yellow-green (505/515) polystyrene fluorescent nanospheres of 100, 250, and 500nm radii with a specific gravity of 1.055. To ensure the measurement accuracy, special care is taken to minimize photobleaching of fluorescent particles by adding neutral density filters to optimally reduce the excitation power. The experimental results for parallel MSDs to the solid surface validate the theory of hindered diffusion [A. J. Goldman, R. G. Cox, and H. Brenner, “Slow viscous motion of a sphere parallel to a plane—I: Motion through a quiescent fluid,” Chem. Eng. Sci. 22, 637 (1967)] of spheres based on viscous slow-down in the near-wall region. It is also reported that the effect of adding sodium chloride up to 10mM to the solut...

Enzyme Reactions in Nanoporous, Picoliter Volume Containers

Advancements in nanoscale fabrication allow creation of small-volume reaction containers that can facilitate the screening and characterization of enzymes. A porous, ∼19 pL volume vessel has been used in this work to carry out enzyme reactions under varying substrate concentrations. Assessment of small-molecule and green fluorescent protein diffusion from the vessels indicates that pore sizes on the order of 10 nm can be obtained, allowing capture of proteins and diffusive exchange of small molecules. Glucose oxidase and horseradish peroxidase can be contained in these structures and diffusively fed with a solution containing glucose and the fluorogenic substrate amplex red through the engineered nanoscale pore structure. Fluorescent microscopy was used to monitor the reaction, which was carried out under microfluidic control. Kinetic characteristics of the enzyme (K(m) and V(max)) were evaluated and compared with results from conventional scale reactions. These picoliter, nanoporous containers can facilitate quick determination of enzyme kinetics in microfluidic systems without the requirement of surface tethering and can be used for applications in drug discovery, clinical diagnostics, and high-throughput screening.

Cell adhesion property affected by cyclooxygenase and lipoxygenase: Opto-electric approach.

Expression of cyclooxygenases (COX) and lipoxygenases (LOX) has been linked to many pathophysiological phenotypes, including cell adhesion. However, many current approaches to measure cellular changes are performed only in a fixed-time point. Since cells dynamically move in conjunction with the cell matrix, there is a pressing need for dynamic or time-dependent methods for the investigation of cell properties. In the presented study, we used stable human colorectal cancer cell lines ectopically expressing COX-1, COX-2, and 15LOX-1, to investigate whether expression of COX-1, COX-2, or 15LOX-1 would affect cell adhesion using our opto-electric methodology. In a fixed-time point experiment, only COX-1- and COX-2-expressing cells enhanced phosphorylation of focal adhesion kinase, but all the transfected cells showed invasion activity. However, in a real-time experiment using opto-electric approaches, transmitted cellular morphology was much different with tight adhesion being shown in COX-2 expressing cells, as imaged by differential interference contrast microscopy (DICM) and interference reflection contrast microscopy (IRCM). Furthermore, micro-impedance measurements showed a continued increase in both resistance and reactance of COX- and LOX-transfected cells, consistent with the imaging data. Our data indicate that both COX- and LOX-expressing cells have strong cell-to-cell and cell-to-substrate adhesions, and that cell imaging analysis with cell impedance data generates fully reliable results on cell adhesion measurement.

Simultaneous dynamic optical and electrical properties of endothelial cell attachment on indium tin oxide bioelectrodes

This study quantifies the dynamic attachment and spreading of porcine pulmonary artery endothelial cells (PPAECs) on optically thin, indium tin oxide (ITO) biosensors using simultaneous differential interference contrast microscopy (DICM) and electrical microimpedance spectroscopy. A lock-in amplifier circuit monitored the impedance of PPAECs cultivated on the transparent ITO bioelectrodes as a function of frequency between 10 Hz and 100 kHz and as a function of time, while DICM images were simultaneously acquired. A digital image processing algorithm quantified the cell-covered electrode area as a function of time. The results of this study show that the fraction of the cell-covered electrode area is in qualitative agreement with the electrical impedance during the attachment phase following the cell settling on the electrode surface. The possibility of several distinctly different states of electrode coverage and cellular attachment giving rise to similar impedance signals is discussed.