• Journal of Sensor Science and Technology
• /
• v.32 no.1
• /
• pp.1-9
• /
• 2023

Recently, the digital healthcare technologies including non-invasive diagnostics based on Internet of Things (IOT) are getting attention. Human exhaled breath contains a variety of volatile organic compounds (VOCs), which can provide information of malfunctions of the body and presence of a specific disease. Detection of VOCs in exhaled breath using gas sensors are easy to use, safe, and cost-effective. However, accurate diagnosis of diseases is challenging because changes in concentration of VOCs are extremely small and lots of body factors directly or indirectly influence to the conditions. To overcome the limitations, highly selective nanosensors and artificial intelligent electronic nose (E-nose) systems have been mainly researched in recent decades. This review provides brief reviews of the recent studies for diabetes and lung cancer diagnosis using nanosensors and E-nose systems.

• Journal of the Korea Safety Management & Science
• /
• v.11 no.3
• /
• pp.73-78
• /
• 2009

In this paper, we developed the care system for older people living alone using the RFID technologies and the living informations. The care system store living informations, extracted through a unconstrained detection method by the RFID tags and readers, into a monitering server. The unconstrained detection method improved a weakness of existing systems that detected a living informations through an infrared sensor, ultrasonic sensor, camera, consumed quantity of the tap water or gas. The result of this study will playa very important role, as a part of a composite older-welfare services. Also, in the future, accumulated living informations will be allowed for a health data of older peoples.

• Journal of the Korean institute of surface engineering
• /
• v.54 no.5
• /
• pp.260-266
• /
• 2021

Synthesizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate highly efficient gas sensors by means of possible enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned zinc oxide (ZnO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the ZnO nanorods array of the single hexagonal wurtzite crystalline phase. From gas sensing measurements for the nitrogen dioxide (NO₂) gas, the vertically aligned ZnO nanorod array is observed to have a highly responsive sensitivity to NO₂ gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO₂ at 250 ℃ and a low NO₂ detection limit of 5 ppm in dry air. These results along with a facile fabrication process demonstrate that the ZnO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO₂ gas sensors.

• Journal of the Korean institute of surface engineering
• /
• v.56 no.4
• /
• pp.219-226
• /
• 2023

Utilizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate relevant gas sensors by means of potential enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned cupric oxide (CuO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a CuO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Cu metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the CuO nanorods array of the single monoclinic tenorite crystalline phase. From gas sensing measurements for the nitrogen monoxide (NO) gas, the vertically aligned CuO nanorod array is observed to have a highly responsive sensitivity to NO gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO at 200 ℃ and a low NO detection limit of 2 ppm in dry air. These results along with a facile fabrication process demonstrate that the CuO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO gas sensors.

• Journal of the Korean Institute of Gas
• /
• v.15 no.4
• /
• pp.27-32
• /
• 2011

Management of gas safety is becoming important with increasing use of gas facilities. U-safety system is being promoted as part of national management of gas, and thus real-time and in-situ gas sensor should be developed. Detection method for When the gas sensor is installed in gas conduit, explosion may be likely, because hydrocarbon gases is usually used the difference of thermal resistance between reference and working electrode. Therefore, it is required to detect the hydrocarbons, such as $CH_4$ and CO, at room temperature via electrochemically catalytic reaction. In this study, Pt nanoparticle was doped on the porous gold powder by electrolytic plating method, and then it was used as catalytic electrode for CO oxidation. For Pt/PAu electrode, approximately 21% of CO conversion was obtained. It is noted that Pt/PAu electrode could be used to react the oxidation of hydrocarbon gases at room temperature via applying of external voltage.

• Korean Journal of Materials Research
• /
• v.24 no.3
• /
• pp.152-158
• /
• 2014

We report the effect of the fabric of the surface microstructure on the CO gas sensing properties of $SnO_2$ thin films deposited on self-assembled Au nanodots ($SnO_2$/Au) that were formed on $SiO_2/Si$ substrates. We characterized structural and morphological properties, comparing them to those of $SnO_2$ thin films deposited directly onto $SiO_2/Si$ substrates. We observed a significant enhancement of CO gas sensing properties in the $SnO_2$/Au gas sensors, specifically exhibiting a high maximum response at $200^{\circ}C$ and quite a low detection limit of 1 ppm level in dry air. In particular, the response of the $SnO_2/Au$ gas sensor was found to reach the maximum value of 32.5 at $200^{\circ}C$, which is roughly 27 times higher than the response (~1.2) of the $SnO_2$ gas sensor obtained at the same operating temperature of $200^{\circ}C$. Furthermore, the $SnO_2/Au$ gas sensors displayed very fast response and recovery behaviors. The observed enhancement in the CO gas sensing properties of the $SnO_2/Au$ sensors is mainly ascribed to the formation of a nanostructured morphology in the active $SnO_2$ layer having a high specific surface-reaction area by the insertion of a nanodot form of Au nucleation layer.

• Journal of Sensor Science and Technology
• /
• v.23 no.3
• /
• pp.207-210
• /
• 2014

$TiO_2$ oxide semiconductor is being widely studied in various applications such as photocatalyst and photosensor. Pd/$TiO_2$ gas sensor is mainly used to detect $H_2$, CO and ethanol. This study focus on increasing hydrogen detection ability of Pd/$TiO_2$ in room temperature through Al-doping. Pd/$TiO_2$ was fabricated by the hydrothermal method. Contacting to Aluminum (Al) foil led to Al doping effect in Pd/$TiO_2$ by thermal diffusion and enhanced hydrogen sensing response. $TiO_2$ nanoparticles were sized at ~30 nm of diameter from scanning electron microscope (SEM) and maintained anatase crystal structure after Al doping from X-ray diffraction analysis. Presence of Al in $TiO_2$ was confirmed by X-ray photoelectron spectroscopy at 73 eV. SEM-energy dispersive spectroscopy measurement also confirmed 2 wt% Al in Pd/$TiO_2$ bulk. The gas sensing test was performed with $O_2$, $N_2$ and $H_2$ gas ambient. Pd/Al-doped $TiO_2$ did not response $O_2$ and $N_2$ gas in vacuum except $H_2$. Finally, the normalized resistance ratio ($R_{H2on}/R_{H2off}$) of Pd/Al-doped $TiO_2$ increases about 80% compared to Pd/$TiO_2$.

• Journal of Sensor Science and Technology
• /
• v.29 no.2
• /
• pp.93-99
• /
• 2020

A colorimetric paper sensor was used to detect volatile nitrogen-containing compounds emitted from spoiled salmon filets to determine their freshness. The sensing mechanism was based on acid-base reactions between acidic pH-indicating dyes and basic volatile ammonia and amines. A sensing layer was simply fabricated by drop-casting a dye solution of bromocresol green (BCG) on a polyvinylidene fluoride substrate, and its color-change response was enhanced by optimizing the amounts of additive chemicals, such as polyethylene glycol, p-toluene sulfonic acid, and graphene oxide in the dye solution. To avoid the adverse effects of water vapor, both faces of the sensing layer were enclosed by using a polyethylene terephthalate film and a gas-permeable microporous polytetrafluoroethylene sheet, respectively. When exposed to basic gas analytes, the paper-like sensor distinctly exhibited a color change from initially yellow, then to green, and finally to blue due to the deprotonation of BCG via the Brønsted acid-base reaction. The use of ammonia analyte as a test gas confirmed that the sensing performance of the optimized sensor was reversible and excellent (detection time of < 15 min, sensitive naked-eye detection at 0.25 ppm, good selectivity to common volatile organic gases, and good stability against thermal stress). Finally, the coloration intensity of the sensor was quantified as a function of the storage time of the salmon filet at 28℃ to evaluate its usefulness in monitoring of the food freshness with the measurement of the total viable count (TVC) of microorganisms in the food. The TVC value increased from 3.2 × 10⁵ to 3.1 × 10⁹ cfu/g in 28 h and then became stable, whereas the sensor response abruptly changed in the first 8 h and slightly increased thereafter. This result suggests that the colorimetric response could be used as an indicator for evaluating the degree of decay of salmon induced by microorganisms.

• Journal of Sensor Science and Technology
• /
• v.20 no.1
• /
• pp.53-57
• /
• 2011

We developed a small methane detection system because methane gas is used in many areas and is dangerous. The developed system consisted of LD(Laser Diode) tuned a wavelength of $1.65\;{\mu}m$, two mirrors to collect a laser beam, photo detector. It could detect methane gas at a long range and its sensitivity was 1.98 V/$CH_4%$.

• Applied Chemistry for Engineering
• /
• v.33 no.6
• /
• pp.630-635
• /
• 2022

Copper(II) oxide (CuO), electroless plated on a nitrogen-containing carbon sponge prepared by a melamine sponge thermal treatment, was developed as a nitric oxide (NO) gas sensor that operates without a wafer. The CuO content on the surface of the carbon sponge increased as the plating time increased, but the content of nitrogen known to induce NO gas adsorption decreased. The untreated carbon sponge showed a maximum resistance change (5.0%) at 18 min. On the other hand, the CuO plated sample (CuO30s-CS) showed a maximum resistance change of 18.3% in 8 min. It is considered that the improvement of the NO gas sensing capability was caused by the increase in hole carriers of the carbon sponge and improved movement of electrons due to CuO. However, the NO gas detection resistance of the CuO electroless plated carbon sponge for 60 s decreased to 1.9%. It is considered that the surface of the carbon sponge was completely plated with CuO, resulting in a decrease in the NO gas adsorption capacity and resistance change. Thus, CuO-plated carbon sponge can be used as an effective NO gas sensor because it has fast and excellent resistance change properties, but CuO should not be completely plated on the surface of the carbon sponge.