Hoyoung Yun - Academia.edu (original) (raw)
Papers by Hoyoung Yun
Biomicrofluidics, 2014
Unwanted sedimentation and attachment of a number of cells onto the bottom channel often occur on... more Unwanted sedimentation and attachment of a number of cells onto the bottom channel often occur on relatively large-scale inlets of conventional microfluidic channels as a result of gravity and fluid shear. Phenomena such as sedimentation have become recognized problems that can be overcome by performing microfluidic experiments properly, such as by calculating a meaningful output efficiency with respect to real input. Here, we present a dual-inlet design method for reducing cell loss at the inlet of channels by adding a new “ upstream inlet ” to a single main inlet design. The simple addition of an upstream inlet can create a vertically layered sheath flow prior to the main inlet for cell loading. The bottom layer flow plays a critical role in preventing the cells from attaching to the bottom of the channel entrance, resulting in a low possibility of cell sedimentation at the main channel entrance. To provide proof-of-concept validation, we applied our design to a microfabricated fl...
A microchip with an expanded channel and a fine particle-analyzing apparatus using the same are p... more A microchip with an expanded channel and a fine particle-analyzing apparatus using the same are provided to increase the working amount of the sample processing by placing the focusing channel even if the speed of the sample and the sheath flows is increased. A microchip comprises a sample channel where the sample is flowed; a sheath flow channel where the sheath flow is flowed; a focusing channel where the sample particles sheath and focused with the sample and the sheath flow are flowed; and an expansion channel for expanding the point circumference of the focusing channel where the sample is analyzed. The focused sample particles keep the focusing status, lower the speed, and improve the detection effect of the sample particles when the focused sample particles pass through the expansion channel.
Flow Cytometry - Recent Perspectives, 2012
Biomedical Applications of Micro- and Nanoengineering III, 2006
Although CD4+ T-cells are an important target of HIV detection, there have been still major probl... more Although CD4+ T-cells are an important target of HIV detection, there have been still major problems in making a diagnosis and monitoring in the third world and the region with few medical facilities. Then, it is necessary to use portable diagnosis devices at low cost when you put an enumeration of CD4+ T-cells. In general, the counting of CD4 below
Microsystem Technologies, 2006
In this paper, we present a novel flow manipulation and signal detection scheme for a microfabric... more In this paper, we present a novel flow manipulation and signal detection scheme for a microfabricated fluorescence-activated cell sorter (μFACS). Optics setup was built on an inverted fluorescence microscope (IX71, Olympus, USA) and microchips were made of PDMS using soft lithography. Perfectly aligned axial illumination setup of the commercial microscope ensures effective signal detection. Hydrodynamic flow manipulation scheme is adopted
Microsystem Technologies, 2008
ABSTRACT Today’s pharmaceutical industry is facing several challenges resulting from a vastly inc... more ABSTRACT Today’s pharmaceutical industry is facing several challenges resulting from a vastly increasing number of samples through a high-throughput screening. In addition, the increased demand for cytotoxicity tests have caused bottlenecks, which in turn is causing serious problems. Here we present a novel approach to performing the cytotoxicity test. This new method uses a directly stackable microsystem on the cultured cells. It also enables us to perform cytotoxicity tests with more reliability by providing exactly the same cell-culture environment for all experiments. The new approach consists of two fascinating modules: First, a serial dilution module can linearly dilute one drug solution into several diluted ones in a serial manner, and equally distribute them into independent microchambers. Secondly, a microcompartment module can firmly attach itself onto any cultured cells and divide the directly-covered cell surface into multiple well-type microchambers instantaneously. This microsystem has a strong feasible advantage. It hardly needs to modify the established cell culture protocols, and at the same time it can eliminate some repetitive and laborious processes. A quick flexible integrated microsystem would reduce many redundant efforts during on-chip cytotoxicity tests.
Lab on a Chip, 2006
This paper presents a novel way of designing a flow focusing channel for microchip flow cytometer... more This paper presents a novel way of designing a flow focusing channel for microchip flow cytometers. With this method we increased throughput and sensitivity of particle detection at the same time. Generally, to increase the detection throughput of a flow cytometer, the speed of the flow inside the focusing channel needs to be increased, hence reducing the time of exposure to laser beam. With the shorter exposure time, both the fluorescence and scatter signal from the target particles become dimmer. To increase the sensitivity of signal detection, however, the speed of the flow should be decreased so as to decrease throughput of detection. To overcome this dilemmatic problem, we integrated an expansion channel inside a focusing channel. Signals from particles in an expansion channel were about 10 times brighter than those in a normal channel. With this enhanced sensitivity, we could also speed up the inlet flow, which in turn increases the overall throughput of detection.
Journal of the Korean Physical Society, 2007
In this article, we report a novel combined microchannel-type erythrocyte deformability test with... more In this article, we report a novel combined microchannel-type erythrocyte deformability test with optical tweezers which can enhance the level of sensitivity with respect to the detection of cancerous diseases. To demonstrate the feasibility of the combined method, we introduce three major parameters, the transit velocity, a modified elongation index, and the shape recovery time of a single erythrocyte in a specifically confined region under dierent powers of an infrared laser. These parameters are geometrically determined and experimentally evaluated for a special blood-related disease, leukemia. The results support this method has a good detection sensitivity enough to pinpoint a minor dierence in the deformability between individual erythrocytes. Furthermore, such a complementary combination of optical tweezers with microfluidic structures will be helpful for comprehensively understanding what significant eect the mechanical properties of erythrocytes have on the multiple chemical reactions inside a living erythrocyte.
Journal of Nanoscience and Nanotechnology, 2011
A novel approach to 3-D information processing of 2-D cell images is presented, called fluorescen... more A novel approach to 3-D information processing of 2-D cell images is presented, called fluorescence intensity ratio stereoscopic transform (FIRST). Here, we describe its basic principle of image processing and show the results for the ratio of total internal reflection fluorescence (TIRF) to fluorescence intensity. A simple, intuitive transform algorithm would help us to easily obtain a clear stereoscopic image from two 2-D cell images with different fluorescence intensity. For this purpose, nonlinear evanescent-field (EF) imaging of cell-membrane surface and its intracellular structures by using on-chip grating coupler is achieved. This method enabled us to obtain cell images with different signal-to-background ratio and resolution under microfluidic environments. Specifically, we manipulated optic pathway to partially illuminate microscale objects within the microfluidic channel. These findings imply this method will enable selectively to detect optical signals of biomolecular interaction within the cell membrane in a controlled manner. Furthermore, we believe this approach will help to develop an optofluidic sensor for individually detecting dynamic behaviors of intracellular molecules in living cells under microfluidic cell culture environments.
Journal of Micromechanics and Microengineering, 2006
Journal of Mechanical Science and Technology, 2009
Japanese Journal of Applied Physics, 2011
Among various bonding methods for polymeric microfluidic chips, solvent-based bonding techniques ... more Among various bonding methods for polymeric microfluidic chips, solvent-based bonding techniques present a relatively high bonding strength and a simple bonding process. However, there are still several considerations for bonding success: the bonding time to achieve a high throughput and a low temperature, and the clogging issue from the solvent overflowing into microfluidic channels. In this work, a novel design method and fabrication of microfluidic chips with solvent-based bonding without microchannel clogging are demonstrated. These microfluidic chips could be bonded in just 10 s at room temperature without additional steps or materials. By using the capillary force inequality caused by height differences between the inside and outside of the microchannel, we could control the solvent movement for bonding two chips. In conclusion, the tunable microchips obtained by the proposed solvent bonding technology might make mass production possible.
Biomicrofluidics, 2014
Unwanted sedimentation and attachment of a number of cells onto the bottom channel often occur on... more Unwanted sedimentation and attachment of a number of cells onto the bottom channel often occur on relatively large-scale inlets of conventional microfluidic channels as a result of gravity and fluid shear. Phenomena such as sedimentation have become recognized problems that can be overcome by performing microfluidic experiments properly, such as by calculating a meaningful output efficiency with respect to real input. Here, we present a dual-inlet design method for reducing cell loss at the inlet of channels by adding a new “ upstream inlet ” to a single main inlet design. The simple addition of an upstream inlet can create a vertically layered sheath flow prior to the main inlet for cell loading. The bottom layer flow plays a critical role in preventing the cells from attaching to the bottom of the channel entrance, resulting in a low possibility of cell sedimentation at the main channel entrance. To provide proof-of-concept validation, we applied our design to a microfabricated fl...
A microchip with an expanded channel and a fine particle-analyzing apparatus using the same are p... more A microchip with an expanded channel and a fine particle-analyzing apparatus using the same are provided to increase the working amount of the sample processing by placing the focusing channel even if the speed of the sample and the sheath flows is increased. A microchip comprises a sample channel where the sample is flowed; a sheath flow channel where the sheath flow is flowed; a focusing channel where the sample particles sheath and focused with the sample and the sheath flow are flowed; and an expansion channel for expanding the point circumference of the focusing channel where the sample is analyzed. The focused sample particles keep the focusing status, lower the speed, and improve the detection effect of the sample particles when the focused sample particles pass through the expansion channel.
Flow Cytometry - Recent Perspectives, 2012
Biomedical Applications of Micro- and Nanoengineering III, 2006
Although CD4+ T-cells are an important target of HIV detection, there have been still major probl... more Although CD4+ T-cells are an important target of HIV detection, there have been still major problems in making a diagnosis and monitoring in the third world and the region with few medical facilities. Then, it is necessary to use portable diagnosis devices at low cost when you put an enumeration of CD4+ T-cells. In general, the counting of CD4 below
Microsystem Technologies, 2006
In this paper, we present a novel flow manipulation and signal detection scheme for a microfabric... more In this paper, we present a novel flow manipulation and signal detection scheme for a microfabricated fluorescence-activated cell sorter (μFACS). Optics setup was built on an inverted fluorescence microscope (IX71, Olympus, USA) and microchips were made of PDMS using soft lithography. Perfectly aligned axial illumination setup of the commercial microscope ensures effective signal detection. Hydrodynamic flow manipulation scheme is adopted
Microsystem Technologies, 2008
ABSTRACT Today’s pharmaceutical industry is facing several challenges resulting from a vastly inc... more ABSTRACT Today’s pharmaceutical industry is facing several challenges resulting from a vastly increasing number of samples through a high-throughput screening. In addition, the increased demand for cytotoxicity tests have caused bottlenecks, which in turn is causing serious problems. Here we present a novel approach to performing the cytotoxicity test. This new method uses a directly stackable microsystem on the cultured cells. It also enables us to perform cytotoxicity tests with more reliability by providing exactly the same cell-culture environment for all experiments. The new approach consists of two fascinating modules: First, a serial dilution module can linearly dilute one drug solution into several diluted ones in a serial manner, and equally distribute them into independent microchambers. Secondly, a microcompartment module can firmly attach itself onto any cultured cells and divide the directly-covered cell surface into multiple well-type microchambers instantaneously. This microsystem has a strong feasible advantage. It hardly needs to modify the established cell culture protocols, and at the same time it can eliminate some repetitive and laborious processes. A quick flexible integrated microsystem would reduce many redundant efforts during on-chip cytotoxicity tests.
Lab on a Chip, 2006
This paper presents a novel way of designing a flow focusing channel for microchip flow cytometer... more This paper presents a novel way of designing a flow focusing channel for microchip flow cytometers. With this method we increased throughput and sensitivity of particle detection at the same time. Generally, to increase the detection throughput of a flow cytometer, the speed of the flow inside the focusing channel needs to be increased, hence reducing the time of exposure to laser beam. With the shorter exposure time, both the fluorescence and scatter signal from the target particles become dimmer. To increase the sensitivity of signal detection, however, the speed of the flow should be decreased so as to decrease throughput of detection. To overcome this dilemmatic problem, we integrated an expansion channel inside a focusing channel. Signals from particles in an expansion channel were about 10 times brighter than those in a normal channel. With this enhanced sensitivity, we could also speed up the inlet flow, which in turn increases the overall throughput of detection.
Journal of the Korean Physical Society, 2007
In this article, we report a novel combined microchannel-type erythrocyte deformability test with... more In this article, we report a novel combined microchannel-type erythrocyte deformability test with optical tweezers which can enhance the level of sensitivity with respect to the detection of cancerous diseases. To demonstrate the feasibility of the combined method, we introduce three major parameters, the transit velocity, a modified elongation index, and the shape recovery time of a single erythrocyte in a specifically confined region under dierent powers of an infrared laser. These parameters are geometrically determined and experimentally evaluated for a special blood-related disease, leukemia. The results support this method has a good detection sensitivity enough to pinpoint a minor dierence in the deformability between individual erythrocytes. Furthermore, such a complementary combination of optical tweezers with microfluidic structures will be helpful for comprehensively understanding what significant eect the mechanical properties of erythrocytes have on the multiple chemical reactions inside a living erythrocyte.
Journal of Nanoscience and Nanotechnology, 2011
A novel approach to 3-D information processing of 2-D cell images is presented, called fluorescen... more A novel approach to 3-D information processing of 2-D cell images is presented, called fluorescence intensity ratio stereoscopic transform (FIRST). Here, we describe its basic principle of image processing and show the results for the ratio of total internal reflection fluorescence (TIRF) to fluorescence intensity. A simple, intuitive transform algorithm would help us to easily obtain a clear stereoscopic image from two 2-D cell images with different fluorescence intensity. For this purpose, nonlinear evanescent-field (EF) imaging of cell-membrane surface and its intracellular structures by using on-chip grating coupler is achieved. This method enabled us to obtain cell images with different signal-to-background ratio and resolution under microfluidic environments. Specifically, we manipulated optic pathway to partially illuminate microscale objects within the microfluidic channel. These findings imply this method will enable selectively to detect optical signals of biomolecular interaction within the cell membrane in a controlled manner. Furthermore, we believe this approach will help to develop an optofluidic sensor for individually detecting dynamic behaviors of intracellular molecules in living cells under microfluidic cell culture environments.
Journal of Micromechanics and Microengineering, 2006
Journal of Mechanical Science and Technology, 2009
Japanese Journal of Applied Physics, 2011
Among various bonding methods for polymeric microfluidic chips, solvent-based bonding techniques ... more Among various bonding methods for polymeric microfluidic chips, solvent-based bonding techniques present a relatively high bonding strength and a simple bonding process. However, there are still several considerations for bonding success: the bonding time to achieve a high throughput and a low temperature, and the clogging issue from the solvent overflowing into microfluidic channels. In this work, a novel design method and fabrication of microfluidic chips with solvent-based bonding without microchannel clogging are demonstrated. These microfluidic chips could be bonded in just 10 s at room temperature without additional steps or materials. By using the capillary force inequality caused by height differences between the inside and outside of the microchannel, we could control the solvent movement for bonding two chips. In conclusion, the tunable microchips obtained by the proposed solvent bonding technology might make mass production possible.