Geon Hwee Kim
Pohang University of Science and Technology
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Publication
Featured researches published by Geon Hwee Kim.
Scientific Reports | 2015
Jung Hwal Shin; Geon Hwee Kim; Intae Kim; Hyungkook Jeon; Taechang An; Geunbae Lim
Liquid pumping can occur along the outer surface of an electrode under a DC electric field. For biological applications, a better understanding of the ionic solution pumping mechanism is required. Here, we fabricated CNT wire electrodes (CWEs) and tungsten wire electrodes (TWEs) of various diameters to assess an ionic solution pumping. A DC electric field created by a bias of several volts pumped the ionic solution in the direction of the negatively biased electrode. The resulting electro-osmotic flow was attributed to the movement of an electric double layer near the electrode, and the flow rates along the CWEs were on the order of picoliters per minute. According to electric field analysis, the z-directional electric field around the meniscus of the small electrode was more concentrated than that of the larger electrode. Thus, the pumping effect increased as the electrode diameter decreased. Interestingly in CWEs, the initiating voltage for liquid pumping did not change with increasing diameter, up to 20 μm. We classified into three pumping zones, according to the initiating voltage and faradaic reaction. Liquid pumping using the CWEs could provide a new method for biological studies with adoptable flow rates and a larger ‘Recommended pumping zone’.
ACS Applied Materials & Interfaces | 2017
Geon Hwee Kim; Taechang An; Geunbae Lim
Despite their advantages in different applications, structural colors are difficult to use because of the inability to change a structural color once it is implemented, as well as their high fabrication costs; implementing multiple structural colors simultaneously on one substrate is a challenge as well. In this study, structural colors were reproduced using quasi-ordered scattering to mitigate these issues. To this end, a ZnO flower-like structure having unimodal distributions of size and spacing was fabricated by ZnO hydrothermal growth. This fabricated nanostructure has a thickness on the order of 103 nm and a diameter on the order of 102 nm. The thickness and diameter increase in proportion with the synthesis time (thickness growth rate = 43 nm/min, diameter growth rate = 20 nm/min). The shape of the nanostructure can be easily tuned by simply adjusting the synthesis and etching times. This method combines the advantages of top-down and bottom-up synthetic approaches in that the structural color can be continuously modified once fabricated.
Sensors | 2015
Intae Kim; Geon Hwee Kim; Chang Sup Kim; Hyung Joon Cha; Geunbae Lim
In whole-cell based biosensors, spectrophotometry is one of the most commonly used methods for detecting organophosphates due to its simplicity and reliability. The sensor performance is directly affected by the cell immobilization method because it determines the amount of cells, the mass transfer rate, and the stability. In this study, we demonstrated that our previously-reported microbe immobilization method, a microbe-attached single-walled carbon nanotube film, can be applied to whole-cell-based organophosphate sensors. This method has many advantages over other whole-cell organophosphate sensors, including high specific activity, quick cell immobilization, and excellent stability. A device with circular electrodes was fabricated for an enlarged cell-immobilization area. Escherichia coli expressing organophosphorus hydrolase in the periplasmic space and single-walled carbon nanotubes were attached to the device by our method. Paraoxon was hydrolyzed using this device, and detected by measuring the concentration of the enzymatic reaction product, p-nitrophenol. The specific activity of our device was calculated, and was shown to be over 2.5 times that reported previously for other whole-cell organophosphate sensors. Thus, this method for generation of whole-cell-based OP biosensors might be optimal, as it overcomes many of the caveats that prevent the widespread use of other such devices.
Scientific Reports | 2018
Geon Hwee Kim; Jung Hwal Shin; Taechang An; Geunbae Lim
Transparent conducting electrodes (TCE) are widely used in a variety of applications including displays, light-emitting diodes (LEDS), and solar cells. An important factor in TCE design is active control of the sheet resistance and transparency; as these are inversely proportional, it is essential to develop a technology that can maintain high transparency, while actively controlling sheet resistance, for a range of applications. Here, a nanofiber network was fabricated based on direct electrospinning onto a three-dimensional (3-D) complex substrate; flat metal electrodes without junction resistance were produced using heat treatment and electroless deposition. The fabricated transparent electrode exhibited a transparency of over 90% over the entire visible light range and a sheet resistance of 4.9 ohms/sq. Adhesion between the electrode and substrate was superior to other electrospinning-based transparent electrodes. The performance of the transparent electrode was verified by measurements taken while using the electrode as a heater; a maximum temperature of 210 °C was achieved. The proposed copper nanofiber-based heater electrode offers the advantages of transparency as well as application to complex 3-D surfaces.
Nanoscale Research Letters | 2018
Geon Hwee Kim; Taechang An; Geunbae Lim
Structural color was generated using electrospinning and hydrothermal growth of zinc oxide (ZnO). An aligned seed layer was prepared by electrospinning, and the hydrothermal growth time control was adjusted to generate various structural colors. The structural color changed according to the angle of the incident light. When the light was parallel to the direction of the aligned nanofibers, no pattern was observed. This pattern is referred to as an “optical switching pattern.” Replication using polydimethylsiloxane (PDMS) also enabled the generation of structural colors; this is an attractive approach for mass production. Additionally, the process is quite tunable because additional syntheses and etching can be performed after the patterns have been fabricated.
Nanoscale Research Letters | 2017
WooSeok Choi; Geon Hwee Kim; Jung Hwal Shin; Geunbae Lim; Taechang An
We report a simple method for electrospinning polymers onto flexible, insulating substrates by controlling the wettability of the substrate surface. Water molecules were adsorbed onto the surface of a hydrophilic polymer substrate by increasing the local humidity around the substrate. The adsorbed water was used as the ground electrode for electrospinning. The electrospun fibers were deposited only onto hydrophilic areas of the substrate, allowing for patterning through wettability control. Direct writing of polymer fiber was also possible through near-field electrospinning onto a hydrophilic surface.
Journal of sensor science and technology = 센서학회지 | 2013
Jung Hwal Shin; Geon Hwee Kim; In Tae Kim ; Hoon Lim; Geun Bae Lim
Glass micropipettes are widely used for drug injection in neurological studies. To enable these devices to monitor neural activity simultaneously with drug injection, an electrode such as Ag/AgCl must be located near or inserted into the glass micropipette to detect electrical signals in vivo. Here, we report carbon-nanotube-modified glass micropipettes (CNGs), which have excellent electrochemical properties such as low impedance and large electrochemical surface area suited for neural recording. In addition, using a standard pressure pump, CNGs can deliver drugs to the target region without bending. Because they are based on standard glass micropipettes, CNGs can readily be applied to traditional equipment, creating opportunities to monitor precisely the drug-injected area.
Advanced Materials Interfaces | 2018
Geon Hwee Kim; Hyoryung Nam; WooSeok Choi; Taechang An; Geunbae Lim
Sensors and Actuators B-chemical | 2017
Geon Hwee Kim; Kanghyun Kim; Hyoryung Nam; Kumjae Shin; WooSeok Choi; Jung Hwal Shin; Geunbae Lim
Advanced Materials Interfaces | 2018
Geon Hwee Kim; Hyoryung Nam; WooSeok Choi; Taechang An; Geunbae Lim