The Experts below are selected from a list of 2404671 Experts worldwide ranked by ideXlab platform
Deirdre R. Meldrum - One of the best experts on this subject based on the ideXlab platform.
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thin pdms films using long spin times or tert butyl alcohol as a solvent
PLOS ONE, 2009Co-Authors: John H Koschwanez, Robert Carlson, Deirdre R. MeldrumAbstract:Thin polydimethylsiloxane (PDMS) films are frequently used in “lab on a chip” Devices as flexible membranes. The common solvent used to dilute the PDMS for thin films is hexane, but hexane can swell the underlying PDMS substrate. A better solvent would be one that dissolves uncured PDMS but doesn't swell the underlying substrate. Here, we present protocols and spin curves for two alternatives to hexane dilution: longer spin times and dilution in tert-butyl alcohol. The thickness of the PDMS membranes under different spin speeds, spin times, and PDMS concentrations was measured using an optical profilometer. The use of tert-butyl alcohol to spin thin PDMS films does not swell the underlying PDMS substrate, and we have used these films to construct multilayer PDMS Devices.
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phosphorescence lifetime based oxygen micro sensing using a digital micromirror device
Optics Express, 2007Co-Authors: Shihhui Chao, Sarah C Mcquaide, Steven A Gales, Mark R. Holl, Deirdre R. MeldrumAbstract:A digital light modulation microscope (DLMM) that utilizes a digital micromirror device (DMD) on an epifluorescence microscope has been developed to modulate excitation light in spatial and temporal domains for phosphorescence lifetime detection. Local O2 concentration can be inferred through the detected lifetime around an O2-quenching phosphorescent porphyrin microsensor. Combined with microsensor arrays, the DLMM can sequentially address light to each microsensor element to construct a discrete lifetime image or O2 distribution. In contrast to conventional phosphorescence lifetime imaging, the new method eliminates the need for a pulsed light source and a time-gated camera. To demonstrate O2 sensing with Lab-on-a-Chip Devices, an array of 150-µm-diameter micro-wells coated with phosphorescent porphyrin were observed. The locations of the sensor elements were automatically identified though image analysis. The goal of this platform is to measure the O2 consumption of individual cells trapped in the microwells.
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oxygen concentration measurement with a phosphorescence lifetime based micro sensor array using a digital light modulation microscope
Biomedical optics, 2006Co-Authors: Shihhui Chao, Sarah C Mcquaide, Mark R. Holl, Deirdre R. MeldrumAbstract:A digital light modulation microscope (DLMM) using a digital micro-mirror device (DMD, Texas Instruments) has been developed to enable detection of O 2 concentration in micro-bioreactors using O 2 -quenching porphyrin phosphorescent dyes. The emission intensity and phosphorescence lifetime of such dyes are both a function of O 2 concentration. While emission intensity can vary in these dye systems as a function of concentration and illumination intensity, phosphorescence lifetime is primarily sensitive to only O 2 concentration. In contrast to conventional phosphorescence lifetime imaging, the DLMM eliminates the need for a pulsed light source, scanning mirrors, or a high-speed camera for time-gated imaging. This technique can selectively address structured light illumination to each sensor location, which is a beneficial feature for analysis of large micro-sensor arrays within Lab-on-a-Chip Devices. The mirrors on the DMD perform as electronically addressable optical switches, each having a ~15 μs switching time, shorter than the phosphorescence lifetimes of potential O 2 sensing dyes (~25-100 μs). The structured light pattern of the DMD and the switching rate of the mirrors are controlled by a PC. An arc lamp illuminates the DMD uniformly and then projects to the specimen through a filter cube for the selected phosphorescent sensor compound. The emitted light returns to the filter cube and is detected by a photo multiplier tube (PMT). An oscilloscope is used to record the emission signal waveform from the PMT. To demonstrate O 2 sensing with Lab-on-a-Chip Devices, an array of 150-μm-diameter micro-wells coated with phosphorescent porphyrin were observed using the DLMM. The goal of this platform is to measure the O 2 consumption of individual cells trapped in the microwells.
Frieder Mugele - One of the best experts on this subject based on the ideXlab platform.
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contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids
Applied Physics Letters, 2018Co-Authors: Niels Mendel, Davood Baratian, Frieder MugeleAbstract:Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including Lab-on-a-Chip Devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, short range chemical interactions, viscous oil entrainment, and electrostatic stresses, we find that this observation can be explained by progressive thinning of the oil layer underneath the drop with increasing voltage. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.
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contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids
arXiv: Fluid Dynamics, 2018Co-Authors: Niels Mendel, Davood Baratian, Frieder MugeleAbstract:Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including Lab-on-a-Chip Devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, viscous oil entrainment and electrostatic stresses, we find that this observation can be explained by progressive thinning with increasing voltage of the oil layer underneath the drop. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.
Shihhui Chao - One of the best experts on this subject based on the ideXlab platform.
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phosphorescence lifetime based oxygen micro sensing using a digital micromirror device
Optics Express, 2007Co-Authors: Shihhui Chao, Sarah C Mcquaide, Steven A Gales, Mark R. Holl, Deirdre R. MeldrumAbstract:A digital light modulation microscope (DLMM) that utilizes a digital micromirror device (DMD) on an epifluorescence microscope has been developed to modulate excitation light in spatial and temporal domains for phosphorescence lifetime detection. Local O2 concentration can be inferred through the detected lifetime around an O2-quenching phosphorescent porphyrin microsensor. Combined with microsensor arrays, the DLMM can sequentially address light to each microsensor element to construct a discrete lifetime image or O2 distribution. In contrast to conventional phosphorescence lifetime imaging, the new method eliminates the need for a pulsed light source and a time-gated camera. To demonstrate O2 sensing with Lab-on-a-Chip Devices, an array of 150-µm-diameter micro-wells coated with phosphorescent porphyrin were observed. The locations of the sensor elements were automatically identified though image analysis. The goal of this platform is to measure the O2 consumption of individual cells trapped in the microwells.
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oxygen concentration measurement with a phosphorescence lifetime based micro sensor array using a digital light modulation microscope
Biomedical optics, 2006Co-Authors: Shihhui Chao, Sarah C Mcquaide, Mark R. Holl, Deirdre R. MeldrumAbstract:A digital light modulation microscope (DLMM) using a digital micro-mirror device (DMD, Texas Instruments) has been developed to enable detection of O 2 concentration in micro-bioreactors using O 2 -quenching porphyrin phosphorescent dyes. The emission intensity and phosphorescence lifetime of such dyes are both a function of O 2 concentration. While emission intensity can vary in these dye systems as a function of concentration and illumination intensity, phosphorescence lifetime is primarily sensitive to only O 2 concentration. In contrast to conventional phosphorescence lifetime imaging, the DLMM eliminates the need for a pulsed light source, scanning mirrors, or a high-speed camera for time-gated imaging. This technique can selectively address structured light illumination to each sensor location, which is a beneficial feature for analysis of large micro-sensor arrays within Lab-on-a-Chip Devices. The mirrors on the DMD perform as electronically addressable optical switches, each having a ~15 μs switching time, shorter than the phosphorescence lifetimes of potential O 2 sensing dyes (~25-100 μs). The structured light pattern of the DMD and the switching rate of the mirrors are controlled by a PC. An arc lamp illuminates the DMD uniformly and then projects to the specimen through a filter cube for the selected phosphorescent sensor compound. The emitted light returns to the filter cube and is detected by a photo multiplier tube (PMT). An oscilloscope is used to record the emission signal waveform from the PMT. To demonstrate O 2 sensing with Lab-on-a-Chip Devices, an array of 150-μm-diameter micro-wells coated with phosphorescent porphyrin were observed using the DLMM. The goal of this platform is to measure the O 2 consumption of individual cells trapped in the microwells.
Niels Mendel - One of the best experts on this subject based on the ideXlab platform.
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contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids
Applied Physics Letters, 2018Co-Authors: Niels Mendel, Davood Baratian, Frieder MugeleAbstract:Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including Lab-on-a-Chip Devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, short range chemical interactions, viscous oil entrainment, and electrostatic stresses, we find that this observation can be explained by progressive thinning of the oil layer underneath the drop with increasing voltage. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.
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contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids
arXiv: Fluid Dynamics, 2018Co-Authors: Niels Mendel, Davood Baratian, Frieder MugeleAbstract:Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including Lab-on-a-Chip Devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, viscous oil entrainment and electrostatic stresses, we find that this observation can be explained by progressive thinning with increasing voltage of the oil layer underneath the drop. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.
Xiangchun Xuan - One of the best experts on this subject based on the ideXlab platform.
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microfluidic separation of live and dead yeast cells using reservoir based dielectrophoresis
Biomicrofluidics, 2012Co-Authors: Saurin Patel, Daniel Showers, Pallavi Vedantam, Tzuenrong J Tzeng, Shizhi Qian, Xiangchun XuanAbstract:Separating live and dead cells is critical to the diagnosis of early stage diseases and to the efficacy test of drug screening, etc. This work demonstrates a novel microfluidic approach to dielectrophoretic separation of yeast cells by viability. It exploits the cell dielectrophoresis that is induced by the inherent electric field gradient at the reservoir-microchannel junction to selectively trap dead yeast cells and continuously separate them from live ones right inside the reservoir. This approach is therefore termed reservoir-based dielectrophoresis (rDEP). It has unique advantages as compared to existing dielectrophoretic approaches such as the occupation of zero channel space and the elimination of any mechanical or electrical parts inside microchannels. Such an rDEP cell sorter can be readily integrated with other components into Lab-on-a-Chip Devices for applications to biomedical diagnostics and therapeutics.
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joule heating in electrokinetic flow
Electrophoresis, 2008Co-Authors: Xiangchun XuanAbstract:Electrokinetic flow is an efficient means to manipulate liquids and samples in Lab-on-a-Chip Devices. It has a number of significant advantages over conventional pressure-driven flow. However, there exists inevitable Joule heating in electrokinetic flow, which is known to cause temperature variations in liquids and draw disturbances to electric, flow and concentration fields via temperature-dependent material properties. Therefore, both the throughput and the resolution of analytic studies performed in microfluidic Devices are affected. This article reviews the recent progress on the topic of Joule heating and its effect in electrokinetic flow, particularly the theoretical and experimental accomplishments from the aspects of fluid mechanics and heat/mass transfer. The primary focus is placed on the temperature-induced flow variations and the accompanying phenomena at the whole channel or chip level.
