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Determination of organic compounds in water using ultraviolet LED
Kim, Chihoon,Ji, Taeksoo,Eom, Joo Beom IOP Pub 2018 Measurement science & technology Vol. No.
<P>This paper describes a method of detecting organic compounds in water using an ultraviolet LED (280 nm) spectroscopy system and a photodetector. The LED spectroscopy system showed a high correlation between the concentration of the prepared potassium hydrogen phthalate and that calculated by multiple linear regression, indicating an adjusted coefficient of determination ranging from 0.953–0.993. In addition, a comparison between the performance of the spectroscopy system and the total organic carbon analyzer indicated that the difference in concentration was small. Based on the close correlation between the spectroscopy and photodetector absorbance values, organic measurement with a photodetector could be configured for monitoring.</P>
ZnO Nanorod-Based Humidity Sensors With Fast Response
Soyoun Jung,Taeksoo Ji IEEE 2014 IEEE electron device letters Vol.35 No.9
<P>Humidity sensors based on ZnO nanorods (NRs) have been developed using a Wheatstone bride (WB) configuration, where the ZnO NRs were selectively grown onto the one quadrant of the WB circuit. It turns out that the WB-based sensor possesses superior performances in terms of response and recovery time, and thermal stability in comparison with conventional types of resistive sensors. Thus, the WB sensor exhibits a fast response and recovery time (~1 s), and temperature-invariant behaviors over a broad range of temperatures up to 180 °C, which is likely because of the self-calibrating and error correction capabilities of the WB circuit itself.</P>
Quasi-Symmetric Wheatstone Bridge Zinc Oxide Nanorod UV Detectors
Vasudevan, Arun,Soyoun Jung,Taeksoo Ji,Ang, Simon S. IEEE 2014 IEEE SENSORS JOURNAL Vol.14 No.9
<P>Zinc oxide (ZnO) nanorod-based ultraviolet (UV) detectors have high responsivity at room temperature due to carrier generation assisted by the depletion region formed by oxygen adsorbed on the surface of nanorods. As such, the amount of oxygen adsorbed on the ZnO nanorod surface and the number of electron-hole pairs that reaches the depletion region on the surface can change the response of the detector. In this paper, the transient responses of metal-semiconductor-metal ZnO nanorod-based UV detectors based on a quasi-symmetric Wheatstone bridge configuration were investigated. Responsivity, defined as the ratio of the Wheatstone bridge detector output current to the total power of the UV light incident on the active area of the detector, as high as 54 A/W was obtained in some of these UV detectors at 30 °C. It was found that the responsivity and the temperature effects on the UV response of the Wheatstone bridge ZnO nanorod UV detectors can be tailored by the difference in the diameters and lengths of the rods grown in the two quadrants.</P>
Aptamer Based SPREETA Sensor for the Detection of Porphyromonas gingivalis G-Protein
Suk-Gyun Park,Hyun Ju Lee,Taeksoo Ji,Kyungbaek Kim,Seung-Ho Ohk The Korean Society for Microbiology and Biotechnol 2024 Journal of microbiology and biotechnology Vol.34 No.2
We have developed an aptamer that specifically binds to Porphyromonas gingivalis to reduce the cellular damage caused by P. gingivalis infection and applied it as a biosensor. P. gingivalis is one of the major pathogens causing destructive periodontal disease among the periodontal microorganisms constituting complex biofilms. Porphyromonas gingivalis G-protein (PGP) known to play an important role in the transmission of germs was used as a target protein for the screening of aptamer. The aptamer that has binds to the G-protein of P. gingivalis, was screened and developed through the Systemic Evolution of Ligands by Exponential Energy (SELEX) method. Modified-Western blot analysis was performed with the aptamer which consisted of 38 single-stranded DNA to confirm the selectivity. ELONA (enzyme linked oligonucleotide assay) used to confirm that the aptamer was sensitive to PGP even at low concentration of 1 ㎍/ml. For the rapid detection of P. gingivalis, we constructed a surface plasmon resonance biosensor with SPREETA using the PGP aptamer. It was confirmed that PGP could be detected as low concentration as at 0.1 pM, which is the minimum concentration of aptamer sensor within 5 min. Based on these results, we have constructed a SPREETA biosensor based on aptamer that can bind to P. gingivalis G-protein. It can be used as an infection diagnosis system to rapidly diagnose and analyze oral diseases caused by P. gingivalis.
Terahertz transmission properties of silicon wafers using continuous-wave terahertz spectroscopy
Kim, Chihoon,Ahn, Jae Sung,Ji, Taeksoo,Eom, Joo Beom IOP 2017 Measurement Science and Technology Vol.28 No.4
<P>We present the spectral properties of Si wafers using continuous-wave terahertz (CW-THz) spectroscopy. By using a tunable laser source and a fixed distributed-feedback laser diode (DFB-LD), a stably tunable beat source for CW-THz spectroscopy system can be implemented. THz radiation is generated in the frequency range of 100 GHz–800 GHz by photomixing in a photoconductive antenna. We also measured CW-THz waveforms by changing the beat frequency and confirmed repeatability through repeated measurement. We calculated the peaks of the THz frequency by taking fast Fourier transforms (FFTs) of measured THz waveforms. The feasibility of CW-THz spectroscopy is demonstrated by the THz spectra of Si wafers with different resistivities, mobilities, and carrier concentrations. The results show that Si wafers with a lower resistivity absorb more THz waves. Thus, we expect our CW-THz system to have the advantage of being able to perform fast non-destructive analysis.</P>
Laser Scabbling of a Concrete Block Using a High-Power Fiber Laser
Oh, Seong Y.,Lim, Gwon,Nam, Sungmo,Kim, TaekSoo,Kim, Ji-Hyun,Chung, Chul-Woo,Park, Hyunmin,Kim, Seonbyeong Korean Radioactive Waste Society 2021 방사성폐기물학회지 Vol.19 No.3
A laser scabbling experiment was performed using a high-power fiber laser to investigate the removal rate of the concrete block and the scabbled depth. Concrete specimens with a 28-day compressive strength of 30 MPa were used in this study. Initially, we conducted the scabbling experiment under a stationary laser beam condition to determine the optimum scan speed. The laser interaction time with the concrete surface varied between 3 s and 40 s. The degree of spalling and vitrification on the surface was primarily dependent on the laser interaction time and beam power. Furthermore, thermal images were captured to investigate the spatial and temporal distribution of temperature during the scabbling process. Based on the experimental results, the scan speed at which the optical head moved over the concrete was set to be 300 mm·min<sup>-1</sup> or 600 mm·min<sup>-1</sup> for the 4.8-kW or 6.8-kW laser beam, respectively. The spalling rates and average depth on the concrete blocks were measured to be 87 cm<sup>3</sup>·min<sup>-1</sup> or 227 cm<sup>3</sup>·min<sup>-1</sup> and 6.9 mm or 9.8 mm with the 4.8-kW or 6.8-kW laser beams, respectively.