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Dive into the research topics where Jeonghun Nam is active.

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Featured researches published by Jeonghun Nam.


Lab on a Chip | 2012

Continuous separation of microparticles in a microfluidic channel via the elasto-inertial effect of non-Newtonian fluid

Jeonghun Nam; Hyunjung Lim; Dookon Kim; Hyun Wook Jung; Sehyun Shin

Pure separation and sorting of microparticles from complex fluids are essential for biochemical analyses and clinical diagnostics. However, conventional techniques require highly complex and expensive labeling processes for high purity separation. In this study, we present a simple and label-free method for separating microparticles with high purity using the elasto-inertial characteristic of a non-Newtonian fluid in microchannel flow. At the inlet, particle-containing sample flow was pushed toward the side walls by introducing sheath fluid from the center inlet. Particles of 1 μm and 5 μm in diameter, which were suspended in viscoelastic fluid, were successfully separated in the outlet channels: larger particles were notably focused on the centerline of the channel at the outlet, while smaller particles continued flowing along the side walls with minimal lateral migration towards the centerline. The same technique was further applied to separate platelets from diluted whole blood. Through cytometric analysis, we obtained a purity of collected platelets of close to 99.9%. Conclusively, our microparticle separation technique using elasto-inertial forces in non-Newtonian fluid is an effective method for separating and collecting microparticles on the basis of size differences with high purity.


Lab on a Chip | 2011

Separation of platelets from whole blood using standing surface acoustic waves in a microchannel

Jeonghun Nam; Hyunjung Lim; Dookon Kim; Sehyun Shin

Platelet separation from blood is essential for biochemical analyses and clinical diagnosis. In this article, we propose a method to separate platelets from undiluted whole blood using standing surface acoustic waves (SSAWs) in a microfluidic device. A polydimethylsiloxane (PDMS) microfluidic channel was fabricated and integrated with interdigitated transducer (IDT) electrodes patterned on a piezoelectric substrate. To avoid shear-induced activation of platelets, the blood sample flow was hydrodynamically focused by introducing sheath flow from two side-inlets and pressure nodes were designed to locate at side walls. By means of flow cytometric analysis, the RBC clearance ratio from whole blood was found to be over 99% and the purity of platelets was close to 98%. Conclusively, the present technique using SSAWs can directly separate platelets from undiluted whole blood with higher purity than other methods.


Biomicrofluidics | 2012

Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave

Jeonghun Nam; Hyunjung Lim; Choong Kim; Ji Yoon Kang; Sehyun Shin

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.


Analytical Chemistry | 2013

Magnetic separation of malaria-infected red blood cells in various developmental stages

Jeonghun Nam; Hui Huang; Hyunjung Lim; Chaeseung Lim; Sehyun Shin

Malaria is a serious disease that threatens the public health, especially in developing countries. Various methods have been developed to separate malaria-infected red blood cells (i-RBCs) from blood samples for clinical diagnosis and biological and epidemiological research. In this study, we propose a simple and label-free method for separating not only late-stage but also early-stage i-RBCs on the basis of their paramagnetic characteristics due to the malaria byproduct, hemozoin, by using a magnetic field gradient. A polydimethylsiloxane (PDMS) microfluidic channel was fabricated and integrated with a ferromagnetic wire fixed on a glass slide. To evaluate the performance of the microfluidic device containing the ferromagnetic wire, lateral displacement of NaNO2-treated RBCs, which also have paramagnetic characteristics, was observed at various flow rates. The results showed excellent agreement with theoretically predicted values. The same device was applied to separate i-RBCs. Late-stage i-RBCs (trophozoites and schizonts), which contain optically visible black dots, were separated with a recovery rate of approximately 98.3%. In addition, using an optimal flow rate, early-stage (ring-stage) i-RBCs, which had been difficult to separate because of their low paramagnetic characteristics, were successfully separated with a recovery rate of 73%. The present technique, using permanent magnets and ferromagnetic wire in a microchannel, can effectively separate i-RBCs in various developmental stages so that it could provide a potential tool for studying the invasion mechanism of the malarial parasite, as well as performing antimalarial drug assays.


international solid-state circuits conference | 2012

A CMOS impedance cytometer for 3D flowing single-cell real-time analysis with ΔΣ error correction

Kang Ho Lee; Jeonghun Nam; Sukhwan Choi; Hyunjung Lim; Sehyun Shin; Gyu-Hyeong Cho

Flow cytometry is an essential cell analysis technology in clinical immunology and haematology for the diagnosis and prognosis of disease. It involves the counting, identification and sorting of cells [1,2]. Conventional bulk measurements [3] require a large volume of blood, which is not desirable for the early detection of a disease, when only a very small percentage of cells contain evidence of the disease. In this paper, we propose, for the first time, a non-invasive and high-throughput single-cell analysis method using CMOS-integrated circuits in conjunction with a microfluidic channel as the first building block of a complete cell-sorting device.


Clinical Hemorheology and Microcirculation | 2011

Measurement of blood coagulation with considering RBC aggregation through a microchip-based light transmission aggregometer.

Hyunjung Lim; Jeonghun Nam; Shubin Xue; Sehyun Shin

Even though blood coagulation can be tested by various methods and techniques, the effect of RBC aggregation on blood coagulation is not fully understood. The present study monitored clot formation in a microchip-based light transmission aggregometer. Citrated blood samples with and without the addition of calcium ion solution were initially disaggregated by rotating a stirrer in the microchip. After abrupt stop of the rotating stirrer, the transmitted light intensity over time was recorded. The syllectogram (light intensity vs. time graph) manifested a rapid increase that is associated with RBC aggregation followed by a decrease that is associated with blood coagulation. The time to reach the peak point was used as a new index of coagulation time (CT) and ranged from 200 to 500 seconds in the present measurements. The CT was inversely proportional to the concentration of fibrinogen, which enhances RBC aggregation. In addition, the CT was inversely proportional to the hematocrit, which is similar to the case of the prothrombin time (PT), as measured by a commercial coagulometer. Thus, we carefully concluded that RBC aggregation should be considered in tests of blood coagulation.


Journal of the Acoustical Society of America | 2012

Continous separation of microparticles using standing surface acoustic wave in microchannel

Sehyun Shin; Jeonghun Nam; Hyunjung Lim

Manipulation of microparticles in heterogeneous complex colloids has become important in various research fields that use microfluidic devices, such as biochemical analyses and clinical diagnosis. Although various techniques for microparticle manipulation in microfluidics have been developed, further advancements are still required for highly accurate analyses. Microparticle manipulation techniques, which include microparticle focusing, tweezing, and separation, using surface acoustic waves (SAWs) have emerged and gained attention. Since SAW-based microfluidics has advantages of being non-invasive, being harmless to particles, and consuming low power intensity and so on, it has great potential for further advancements, especially for biochemical research field. Recently, SAW-based techniques which can manipulate a variety of microparticles have been developed in my group. To predict the behavior of microparticles in microchannel flow, advanced analytical model was developed, and validated with experimenta...


PLOS ONE | 2018

Determination of red blood cell deformability using centrifugal force in a three-dimensional-printed mini-disk (3D-PMD)

Hyunjung Lim; Seung Min Back; Jeonghun Nam; Hyuk Soon Choi

Measuring red blood cell (RBC) deformability has become important for clinical disease diagnostics. Various methods for measuring RBC deformability have been developed; however, they require costly and large instruments, long measuring time, and skilled personnel. In this study, we present a three-dimensional-printed mini-disk (3D-PMD) for measuring RBC deformability to overcome the previous limitations. For a miniaturized and low-cost setup, the 3D-PMD was fabricated by a 3D printing technique, which had not yet been used for fabricating a lab-on-a-compact disk (LOCD). Using a 3D printing technique, a multi-layered fluidic channel on the mini CD could be fabricated easily. During rotation by a spinning motor, the difference of the length of compressed RBCs in the fluidic channel was measured and analysed as compressibility indices (CIs) of normal and glutaraldehyde-treated hardened RBCs. The rotation speed and time were decided as 3000 rpm and 30 min, respectively, at which the difference of CI values between normal and hardened RBCs was largest (CInormal-CIhardened = 0.195).


Microfluidics and Nanofluidics | 2014

Lateral migration of particles suspended in viscoelastic fluids in a microchannel flow

Hyunjung Lim; Jeonghun Nam; Sehyun Shin


Korea-australia Rheology Journal | 2011

Determination of the blood viscosity and yield stress with a pressure-scanning capillary hemorheometer using constitutive models

Byung Kwon Lee; Shubin Xue; Jeonghun Nam; Hyunjung Lim; Sehyun Shin

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