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Total internal reflection fluorescent microscopy (TIRFM) is a relatively well known tool used to examine the near wall region (approximately 1 μm). For years, cellular biologists have used TIRFM in a variety of experiments to examine... more
Total internal reflection fluorescent microscopy (TIRFM) is a relatively well known tool used to examine the near wall region (approximately 1 μm). For years, cellular biologists have used TIRFM in a variety of experiments to examine multiple cell lines. However, much of the research has been somewhat static in nature, considering only initial and final states. With the increased ability to stain specific organelles within cells through the use of green fluorescent protein (GFP), dynamic imaging is becoming a viable solution to previously difficult problems.
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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... more
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.
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Research Interests: Mechanical Engineering, Biology, Cell Adhesion, Medicine, Colorectal cancer, and 15 moreBiological Sciences, Humans, Female, Male, Physical sciences, Colon cancer, Cell Proliferation, Electric Impedance, Nag, Biochemistry and cell biology, Gene expression profiling, Colorectal Neoplasms, Nuance, real time polymerase chain reaction, and reverse transcriptase polymerase chain reaction
Research Interests: Materials Science, Optics, Microscopy, Electrochemistry, Cell Adhesion, and 15 moreNanoparticles, Medicine, Optical Imaging, Optoelectronics, Animals, Biosensor, Optical physics, Optics and Photonics, Electrodes, Electrode, Equipment Design, Electrical And Electronic Engineering, Indium, Indium tin oxide, and Biosensing Techniques
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A conventional microscopy and confocal microscopy was used to enable nano-particle tracking using a three-dimensional (3-D) diffraction image pattern caused by an optical aberration. The Point Spread Function (PSF) of a particle image is... more
A conventional microscopy and confocal microscopy was used to enable nano-particle tracking using a three-dimensional (3-D) diffraction image pattern caused by an optical aberration. The Point Spread Function (PSF) of a particle image is known as a function of a defocus distance from a focal plane. Using the PSF of nano-particles, particle’s x and y positions as well as z-position can be obtained. A dry objective lens (40X, 0.75NA) is used to detect diffraction patterns of 500-nm fluorescent micro-spheres suspended in water solution inside a 100-μm square micro-tube. The purposes of this presented study are to investigate experimentally the 3-D PSF of fluorescent nano-particle in thick specimen and to develop the 3-D particle tracking technique using 3-D diffraction images of conventional microscopy and CLSM.Copyright © 2004 by ASME
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An integrated opto-electric biosensor is developed that uses an optically transparent and electrically conductive indium tin oxide (ITO) thin film coated on a slide glass substrate. This biosensor can simultaneously acquire the... more
An integrated opto-electric biosensor is developed that uses an optically transparent and electrically conductive indium tin oxide (ITO) thin film coated on a slide glass substrate. This biosensor can simultaneously acquire the micro-impedance response and microscopic images of live cells in vitro under various toxic agent stimuli. The dynamic response of live porcine pulmonary artery endothelial cells (PPAECs) exposed to various doses of cytochalasin D are comprehensively examined by monitoring the micro-impedance characteristics at a specified frequency and DICM images using the opto-electric biosensor. The change in PPAEC morphology and motility caused by cytochalasin D clearly illustrates the dose-dependent actin filament disruption where optical images are correlated with the changes in the micro-electric impedance.Copyright © 2007 by ASME
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Research Interests: Mechanical Engineering, Chemistry, Engineering Mechanics, Environmental Health, Biology, and 15 moreImage Analysis, Cell Adhesion, Cell Biology, Adhesion, Colorectal cancer, Cell line, Humans, Cell, Impedance, Electric Impedance, Biochemistry and cell biology, Focal Adhesion Kinase, Differential Interference Contrast, Ircm, and lipoxygenase
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We present a simple microfluidic technique to in-situ photopolymerize (by 365 nm ultraviolet) monodisperse oxidized methacrylated alginate (OMA) microgels using a photoinitiator (VA-086). By this technique, we generated monodisperse... more
We present a simple microfluidic technique to in-situ photopolymerize (by 365 nm ultraviolet) monodisperse oxidized methacrylated alginate (OMA) microgels using a photoinitiator (VA-086). By this technique, we generated monodisperse spherical OMA beads and discoid non-spherical beads with better shape consistency than ionic crosslinking methods do. We found that a high monomer concentration (8 w/v %), a high photoinitiator concentration (1.5 w/v %), and absence of oxygen are critical factors to cure OMA microgels. This photopolymerizing method is an alternative to current methods to form alginate microgels and is a simpler approach to generate non-spherical alginate microgels.
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A comprehensive three-dimensional nano-particle tracking technique in micro- and nano-scale spatial resolution using the Total Internal Reflection Fluorescence Microscope (TIRFM) is discussed. Evanescent waves from the total internal... more
A comprehensive three-dimensional nano-particle tracking technique in micro- and nano-scale spatial resolution using the Total Internal Reflection Fluorescence Microscope (TIRFM) is discussed. Evanescent waves from the total internal reflection of a 488㎚ argon-ion laser are used to measure the hindered Brownian diffusion within few hundred nanometers of a glass-water interface. 200-㎚ fluorescence-coated polystyrene spheres are used as tracers to achieve three-dimensional tracking within the near-wall penetration depth. A novel ratiometric imaging technique coupled with a neural network model is used to tag and track the tracer particles. This technique allows for the determination of the relative depth wise locations of the particles. This analysis, to our knowledge is the first such three-dimensional ratiometric nano-particle tracking velocimetry technique to be applied for measuring Brownian diffusion close to the wall.
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The present study aims to measure the solid–liquid interface temperature of an evaporating droplet on a heated surface using a thermoresponsive polymer. Poly(N-isopropylacrylamide) (pNIPAM) was used owing to its sensitive optical and... more
The present study aims to measure the solid–liquid interface temperature of an evaporating droplet on a heated surface using a thermoresponsive polymer. Poly(N-isopropylacrylamide) (pNIPAM) was used owing to its sensitive optical and mechanical properties to the temperature. We also measured the refractive index variation of the pNIPAM solution by using the surface plasmon resonance imaging (SPRi). In particular, the present study proposed a new method to measure the solid–liquid interface temperature using the correlation among reflectance, refractive index, and temperature. It was found that the reflectance of a pNIPAM solution decreased after the droplet deposition. The solid–liquid interface temperature, estimated from the reflectance, showed a lower value at the center of the droplet, and it gradually increased along the radial direction. The lowest temperature at the contact line region is present because of the maximum evaporative cooling. Moreover, the solid–liquid interface...
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The objective of this work is to identify the mechanism of dropwise condensation on a smooth solid surface. We investigate the stable dropwise condensation that occurs at a droplet growth rate of 1 µm/s in diameter on a gold-coated glass... more
The objective of this work is to identify the mechanism of dropwise condensation on a smooth solid surface. We investigate the stable dropwise condensation that occurs at a droplet growth rate of 1 µm/s in diameter on a gold-coated glass surface. Additionally, we present our observations on unstable dropwise condensation, i.e., degradation of dropwise condensation of steam on a gold surface. Surface Plasmon Resonance Imaging (SPRi) is used to evaluate the existence and structure of thin films and occurrence of initial nuclei during condensation. SPRi approach used in this study has lateral resolutions of 4–10 µm, thickness resolutions of 0.1–1 nm, and temporal resolutions of 200–10,000 frames per second (FPS). Visualization of the onset of stable dropwise condensation suggests droplets form at heterogeneous nucleation sites and that no film greater than a monolayer exists on the surface before the formation of droplets. Observation of the unstable dropwise condensation of steam show...
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Using surface plasmon resonance imaging (SPRi), we have recently shown for the first time the existence of a monolayer water film between droplets during dropwise condensation. This study examines the effect of adsorbed volatile organic... more
Using surface plasmon resonance imaging (SPRi), we have recently shown for the first time the existence of a monolayer water film between droplets during dropwise condensation. This study examines the effect of adsorbed volatile organic compounds (VOCs) on the ultrathin film measurement using SPRi. Further, the work presents the proper surface-treatment process that enables measurements of the ultrathin water layer during high-speed imaging of dropwise condensation at 3000 frame per second. In this study, two methods were applied for cleaning the surface (gold-coated glass)—(1) standard cleaning procedure (SCP) using acetone, isopropyl alcohol, and deionized water and (2) SCP followed by air plasma cleaning. This work discusses the effect of the cleaning procedures on surface roughness, contact angle, and surface chemistry using atomic force microscopy, optical microscopy, and an X-ray photoelectron spectroscope meter. The results showed that SCP before the SPRi is a proper surface-...
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Drop condensation and coalescence is visualized using high-speed Surface Plasmon Resonance (SPR) reflectance microscopy. SPR microscopy is a label-free technique that can characterize thin films (less than 1µm) by detecting the changes in... more
Drop condensation and coalescence is visualized using high-speed Surface Plasmon Resonance (SPR) reflectance microscopy. SPR microscopy is a label-free technique that can characterize thin films (less than 1µm) by detecting the changes in the refractive index of the test medium. The sensing surface is a 50 nm thick gold film on a 2.5 nm thick Ti layer is deposited on a borosilicate substrate. P-polarized monochromatic light (632 nm) is incident on the gold film in a total internal reflection mode. Free electrons in the gold film are excited by the incident light when a resonance condition is met. The result is a decrease in the reflected intensity. Resonance depends upon wavelength, incident angle, and refractive index of prism and test medium. To induce condensation, a water bridge is created between the SPR gold film and an ITO coated glass slide. When the ITO coated slide is heated water evaporates from the bridge and condenses on the gold film. The sequence of images on the proc...
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Using a unique, near-field microscopy technique, fringe patterns and nanoparticle motions are visualized immediately following a nanofluid droplet deposition on a glass substrate in which an air bubble is entrapped. The nanofluid consists... more
Using a unique, near-field microscopy technique, fringe patterns and nanoparticle motions are visualized immediately following a nanofluid droplet deposition on a glass substrate in which an air bubble is entrapped. The nanofluid consists of DI-water, 0.10% Aluminum Oxide nanoparticles with an average diameter of 50 nm, and 0.0005% yellow-green polystyrene fluorescent particles of 1 μm diameter. High-speed, fluorescent-mode confocal imaging enables investigation of depth-wise sectioned particle movements in the nanofluid droplet inside which a bubble is entrapped. The static contact angle is increased when a bubble is applied. In the presence of the bubble in the droplet, the observed flow toward the center of the droplet is opposite to the flow observed in a droplet without the bubble. When the bubble is present, the evaporation process is retarded. Also, random motion is observed in the contact line region instead of the typical evaporation-driven flow toward the droplet edge. Onc...
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A conventional microscopy and confocal microscopy was used to enable nano-particle tracking using a three-dimensional (3-D) diffraction image pattern caused by an optical aberration. The Point Spread Function (PSF) of a particle image is... more
A conventional microscopy and confocal microscopy was used to enable nano-particle tracking using a three-dimensional (3-D) diffraction image pattern caused by an optical aberration. The Point Spread Function (PSF) of a particle image is known as a function of a defocus distance from a focal plane. Using the PSF of nano-particles, particle’s x and y positions as well as z-position can be obtained. A dry objective lens (40X, 0.75NA) is used to detect diffraction patterns of 500-nm fluorescent micro-spheres suspended in water solution inside a 100-μm square micro-tube. The purposes of this presented study are to investigate experimentally the 3-D PSF of fluorescent nano-particle in thick specimen and to develop the 3-D particle tracking technique using 3-D diffraction images of conventional microscopy and CLSM.Copyright © 2004 by ASME
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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... more
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 elec...
Research Interests: Chemistry, Molecular Biology, Biology, Apoptosis, Medicine, and 15 moreGene Silencing, Colorectal cancer, Humans, Complementary Medicine, Chromatin Immunoprecipitation, Cell Proliferation, Molecular Cancer Therapeutics, DNA binding proteins, Antineoplastic Agents, Binding Site, Bioelectrical Impedance, Gene Expression Regulation, Cell Growth, Colorectal Neoplasms, and binding sites
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A review on advanced flow visualization techniques is presented particularly for applications to microscale heat and mass transport measurements. Challenges, development and applications of microscale visualization techniques are... more
A review on advanced flow visualization techniques is presented particularly for applications to microscale heat and mass transport measurements. Challenges, development and applications of microscale visualization techniques are discussed for the study of heating/evaporating thin films, gas bubble advancement in a microchannel, thermophoretic behavior near the solid surface, and microheater fabrications, mainly conducted at the Microscale Fluidics and Heat Transport Laboratory of Texas A&M University. The presented topics include: 1. Fizeau interferometry for thin film thickness measurements. 2. Total Internal Reflection Fluorescence Microscopy (TIRFM) for flow field measurements with 100-nm depth-of-field. 3. Molecular Tagging Fluorescence Velocimetry (MTFV) using 10-nm caged seeding molecules. 4. Ratiometric Laser Induced Fluorescence (LIF) for micro-resolution thermometry. 5. Confocal Laser Scanning Microscopy (CLSM) for optical sectioning with 1.0-μm depthwise resolution. 6. Multi-layer fabrications of microheater arrays with feedback circuit control. Each of these techniques is discussed in three-fold: (1) its operating principle and operation, (2) its application and measurement results, and (3) its future challenges
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Research Interests: Materials Science, Biomedical Engineering, Cell Adhesion, Medicine, Optoelectronics, and 15 moreBiomedical Optics, Endothelial Cells, Animals, Dielectric Spectroscopy, Optical physics, Electrical Properties, Endothelial cell, Swine, Optics and Photonics, Electrodes, Electrode, Electric Impedance, Indium tin oxide, Biosensing Techniques, and Electrical Impedance
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Research Interests: Mechanical Engineering, Biology, Cell Adhesion, Medicine, Colorectal cancer, and 15 moreBiological Sciences, Humans, Female, Male, Physical sciences, Colon cancer, Cell Proliferation, Electric Impedance, Nag, Biochemistry and cell biology, Gene expression profiling, Colorectal Neoplasms, Nuance, real time polymerase chain reaction, and reverse transcriptase polymerase chain reaction
Research Interests: Mechanical Engineering, Chemical Engineering, Chemistry, Analytical Chemistry, Catalysis, and 15 moreKinetics, Fluorescence, Fluorescence Microscopy, Drug Discovery, Medicine, Enzyme Kinetics, Humans, Glucose, Diffusion, High throughput screening, Enzyme, Hydrogen Peroxide, Enzyme activity, CARBOHYDRATES, and Glucose Oxidase
Research Interests: Mechanical Engineering, Materials Science, Chemistry, Fluorescence, Crystallization, and 15 moreNanotechnology, Chemical Physics, Medicine, Multidisciplinary, Numerical Simulation, Diffusion, Nanostructures, Motion, Green Fluorescent Protein, Membrane, Biological systems, Design and Development, Molecular Conformation, Materials Testing, and Membrane Protein
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To understand the physics behind dropwise condensation, a microscopy technique must be able to measure a sub-nanometer film at a high temporal resolution (>1,000 FPS). In this work, automated Surface Plasmon Resonance imaging (SPRi) is... more
To understand the physics behind dropwise condensation, a microscopy technique must be able to measure a sub-nanometer film at a high temporal resolution (>1,000 FPS). In this work, automated Surface Plasmon Resonance imaging (SPRi) is used as a tool to study the existence of a thin film between the dropwise condensate. SPRi is a label-free imaging technique that works based on the attenuated total internal reflection. SPRi can detect changes in the refractive index (RI) of the test medium in the thin region (<300 nm) above the sensing gold layer. The automated, angle-scanning SPRi instrument was developed by integrating linear and rotating motorized stages. This instrument improves conventional SPRi by enhancing the resolution of angle probing, increasing the speed of angle scanning, and minimizing the angle-dependent image artifacts. As a proof of concept, we visualized the three stages of coalescence at 10,000 FPS, including bridge formation, composite peanut-shape droplet ...