• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.1686-1687
• /
• 2011

A microfabricated chip with in-channel electrochemical cell using interdigitated gold electrode was fabricated for sensitive electrochemical analysis. The gold electrodes were fabricated on glass wafer using thermal evaporator and were covered using PDMS mold containing microchannel for analyte and electrolyte. The active area of each electrode was $250\;{\mu}m{\times}200\;{\mu}m$ with a gap of 200 ${\mu}m$ between the electrodes. Microelectrodes results in maximum amplification of signal, since the signal enhancement effect due to cycling of the reduced and oxidized species strongly depends on the inter electrode distance. Analytes such as methylene blue and guanosine were characterized using the fabricated electrodes and their electrochemical characteristics were compared with conventional bulk electrodes. The device so developed shall find use as disposable electrochemical cell for rapid and sensitive analysis of electroactive species.

• Journal of the Korean Society of Visualization
• /
• v.1 no.2
• /
• pp.47-51
• /
• 2003

Microfluidic chips such as lab-on-a-chip (LOC) include micro-channels for sample delivery, mixing, reaction, and separation. Pressure driven flow or electro-osmotic flow (EOF) has been usually employed to deliver bio-samples. Having some advantages of easy control, the flow characteristics of EOF in microchannels should be fully understood to effectively control the electro-osmotic pump for bio-sam-pie delivery. In this study, a micro PIV system with an epifluorescence inverted microscope and a cooled CCD was used to measure velocity fields of EOF in a glass microchannel and a PDMS microchannel. The EOF velocity fields were changed with respect to electric charge of seeding particles and microchannel materials used. The EOF has nearly uniform velocity distribution inside the microchannel when pressure gradient effect is negligible. The mean streamwise velocity is nearly proportional to the applied electric field. Glass microchannels give better repeatability in PIV results, compared with PDMS microchannels which are easy to fabricate and more suitable for PIV experiments.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1521_1522
• /
• 2009

Chemotaxis is the directed movement of cells in gradients of signaling molecules, an essential biological process that underlies morhpogenesis during development, and the recruitment of immune cells to sites of infection. Especially, bacterial chemotaxis has utilized as an important prelude to study metabolism, prey-predator relationship, symbiosis, other ecological interactions in microbial communities. Recently, novel analytical formats integrated with microfluidics were introduced to investigate the chemotaxis of the cells with the precise control of chemical gradient and small volume of cells. In this study, we present a method to detect bacterial chemotaxis by direct fluidic contacting. The developed fluidic-handling method is driven by capillary force, hydrophobic barrier and a cohesion force between fluids. We have investigated the chemotactic response of E Coli. and Pseudomonas aeruginosa to three kinds of chemoeffectors such as HEPES buffer, peptone and chloroform.

• Current Optics and Photonics
• /
• v.4 no.1
• /
• pp.44-49
• /
• 2020

In this paper, a new method is presented to measure the refractive index of single plain glass or multilayered materials, based on a laser frequency-shifted confocal feedback microscope. Combining the laser frequency-shifted feedback technique and the confocal effect, the method can attain high axial-positioning accuracy, stability and sensitivity. Measurements of different samples are given, including N-BK7 glass, Silica plain glass, and a microfluidic chip with four layers. The results for N-BK7 glass and Silica plain glass show that the measurement uncertainty in the refractive index is better than 0.001. Meanwhile, the feasibility of this method for multilayered materials is tested. Compared to conventional methods, this system is more compact and has less difficulty in sample processing, and thus is promising for applications in the area of refractive-index measurement.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.4
• /
• pp.392-397
• /
• 2007

We developed a microfluidic platform able to control the trap and release of magnetic beads used for separation of a specific biomolecules. The magnetic beads can be trapped and released conditionally by controlling the difference between the Stokes force induced by the fluid flow and magnetic force resulting from a permanent magnet. The permanent magnet of CoNiP alloy is electroplated. It is characterized to have the 1369 Oe of coercivity, 1762 Gauss of remanence, and 0.603MGOe of (BH)max. Through the experimental and numerical investigation, the magnetic beads are trapped under the flow velocity of 17 ${\mu}m/s$ and are released perfectly above the velocity of 174 ${\mu}m/s$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.209.2-209.2
• /
• 2014

In recent years, researches about hydrophobic and hydrophilic surfaces have been executed however their other effects have not been researched enough. In this paper, the fabrication method of hierarchical structures of micro line array combined with fluorinated wax for anisotropic superomniphobic wettability is presented. We have achieved anisotropic and superomniphobic surface via simple two step methods, which are maskless photolithography and wax deposition. In order to prove how to provide those characteristics, SEM, contact angle measurement tool and X-ray diffraction are used. Fluorinated wax is crystalized self-assembly and it is subordinated on micro line array so that it is able to display anisotropic wettability. Understanding on anisotropic superomniphobic surface and simple fabrication method has been attracted to apply for lots of applications which range from self-cleaning surface, microfluidic chip, to directionally fluid control device, even in oily fluid.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.89-93
• /
• 2005

In this work, perfusive particles are used to form a micro column in a microfluidic chip and flow properties of the micro column are investigated. The packing flow velocity and the column/particle size ratio are shown to be important parameters affecting the packing density of the micro column. Experimental results show that the effect of the column/particle size ratio on the flow resistance of the micro column is negligible. This contrasts with previous works on the effect of the column/particle size ratio on the total pressure drop across the column.

• Journal of the Korean Society of Visualization
• /
• v.13 no.2
• /
• pp.16-21
• /
• 2015

Concentration polarization(CP) phenomena show great potential on desalination technology. As we can control the dimension of silicon based nanochannel system, it can be used to model ion exchange membrane. In this study, to investigate the effect of nanochannel number and working conditions on the CP based desalination process, nanochannel based microfluidic system is fabricated. First, we optimized nanochannel number and working conditions to conduct visualization study on CP based desalination process. Second, we visualized the desalination process with fluorescent dye in the desalination chip. We also visualized that the particles also can be removed by the CP based desalination process.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2460-2464
• /
• 2008

The present paper suggests new method to know the effects of molecular diffusion and the helicity of microchannel flows on mixing in passive micromixers, which are essential components of a microfluidic chip. In this study, 'Helix Index' is newly defined as the magnitude of chaotic advection. Relationship between Helix Index and Mixing Index is analyzed numerically such as the wide range of Peclet and Reynolds numbers in three dimensional serpentine microchannel when using soluble solutions (water/glycerol). As a result, a simple algebraic equation is derived by this relationship based on a regression analysis. The algebraic equation is found to be able to accurately predict the mixing performance without solving the coupled, complex momentum and mass transfer equations.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.4
• /
• pp.231-236
• /
• 2004

A normally open thermopneumaticc-actuated microvalve has been fabricated and their properties are investigated. The advantages of the proposed microvalve are of the low cost fabrication process and the transparent optical property using polydimethylsiloxane (PDMS) and indium tin oxide (ITO) glass. The fabricated microvalves with in-channel configuration are easily integrated with other microfluidic devices on the same substrate. The fabrication process of thermopneumatic-actuated microvalvesusing PDMS is very simple and its performance is very suitable for a disposable lab-on-a-chip. The PDMS membrane deflection increases and the flow rates of the microchannel with microvalvels decrease as the applied power to the ITO heater increases. The powers at flow-off are dependent on the membrane thickness and the applied inlet pressure but are independent of the channel width of microvalves. The flow rate is well controlled by the switching function of ITO heater and the closing/opening times are around 20 sec and 25 sec, respectively.