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Chemiresistive Sensor Array Based on Semiconducting Metal Oxides for Environmental Monitoring
( Hi Gyu Moon ),( Soo Deok Han ),( Min Gyu Kang ),( Woo Suk Jung ),( Ho Won Jang ),( Kwang Soo Yoo ),( Hyung Ho Park ),( Chong Yun Kang ) 한국센서학회 2014 센서학회지 Vol.23 No.1
We present gas sensing performance based on 2Χ2 sensor array with four different elements (TiO2, SnO2, WO3 and In2O3 thin films) fabricated by rf sputter. Each thin film was deposited onto the selected SiO2/Si substrate with Pt interdigitated electrodes (IDEs) of 5m spacing which were fabricated on a SiO2/Si substrate using photolithography and dry etching. For 5 ppm NO2 and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, 2Χ2 sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multifunctional smart sensors for environmental monitoring.
Moon, Hi Gyu,Jung, Youngmo,Han, Soo Deok,Shim, Young-Seok,Jung, Woo-Suk,Lee, Taikjin,Lee, Seok,Park, Jung Han,Baek, Seung-Hyub,Kim, Jin-Sang,Park, Hyung-Ho,Kim, Chulki,Kang, Chong-Yun Elsevier 2018 Sensors and actuators. B Chemical Vol.257 No.-
<P><B>Abstract</B></P> <P>Chemiresistive electronic nose (CEN) composed of villi-like nanostructures (VLNs) of SnO<SUB>2</SUB> and WO<SUB>3</SUB>, and Au-functionalized VLNs was fabricated by applying electron-beam evaporation in a glancing angle deposition mode. The VLNs-based CEN with a back-heater (212°C) shows high responses with low detection limits of parts per billion (ppb)-levels for NO and NH<SUB>3</SUB> vapors at 80% relative humidity atmosphere. The enhanced sensitivities in a high humidity condition turn out to be attributed to the spillover effect by the Au nanoparticles and a large surface-to-volume ratio in porous VLNs. Employing Au NPs on VLNs leads to the increase of O<SUP>−</SUP> ions via the spillover effect which impedes the adsorption of water molecules, maintaining the enhanced responses against environmental humidity. Consequently, high responses for NO and NH<SUB>3</SUB> vapors maintain even in the high humidity condition. Herein, with the principal component analysis (PCA), we demonstrate highly selective detection of NO and NH<SUB>3</SUB> vapors against C<SUB>2</SUB>H<SUB>5</SUB>OH, CO, C<SUB>7</SUB>H<SUB>8</SUB>, C6H6, and CH<SUB>3</SUB>COCH<SUB>3</SUB> vapors. These results open up wide applications of the VLNs-based CEN as an inexpensive and non-invasive diagnostic tool for asthma and kidney disorder.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A villi-like nanostructures (VLNs)-based chemiresistive electronic nose (CEN) as exhaled breath analyzer was developed. </LI> <LI> The VLNs-based CEN exhibits high sensitive detection to NO (Asthma) and NH<SUB>3</SUB> (Kidney disorder) as biomarkers. </LI> <LI> The detection limits (DLs) of the VLNs-based CEN are 899ppt–10.2ppb for NO and 312ppb–639ppb for NH<SUB>3</SUB>, respectively. </LI> <LI> The enhanced responses in humid environment are attribute to the spillover effect by Au nanoparticles. </LI> <LI> The highly selective NO and NH<SUB>3</SUB> detections were clearly distinguished by principal component analysis (PCA). </LI> </UL> </P>
Moon, Hi Gyu,Shim, Young-Seok,Su, Dong,Park, Hyung-Ho,Yoon, Seok-Jin,Jang, Ho Won American Chemical Society 2011 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.115 No.20
<P>Embossed TiO<SUB>2</SUB> thin films with high surface areas were achieved using soft templates composed of monolayer polystyrene beads. The structure of links between beads in the templates could be controlled by varying O<SUB>2</SUB> plasma etching time, resulting in a variety of templates with close-linked, nanolinked, or isolated beads. Room-temperature deposition of TiO<SUB>2</SUB> on the plasma-treated templates and calcination at 550 °C resulted in embossed films with tailored links between anatase TiO<SUB>2</SUB> hollow hemispheres. Although all embossed TiO<SUB>2</SUB> films displayed a similar increase in the surface-to-volume ratio compared with a plain TiO<SUB>2</SUB> thin film, the response of embossed TiO<SUB>2</SUB> films with nanolinked hollow hemispheres to CO or ethanol gases was much higher than the response of films with close-linked or isolated hollow hemispheres. The strong correlation between gas sensitivity and the structure of links between the TiO<SUB>2</SUB> hollow hemispheres revealed the critical importance of tailoring links between individual oxide nanostructures for enhancing gas-sensing properties of the ensemble of the individual nanostructures. The facile and large-scale synthesis of embossed TiO<SUB>2</SUB> films with nanolinked hollow hemispheres on Si substrates and the high sensitivity that is achieved without the aid of additives provide a sustainable competitive advantage over other methods for fabricating highly sensitive metal oxide gas sensors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-20/jp2020325/production/images/medium/jp-2011-020325_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp2020325'>ACS Electronic Supporting Info</A></P>
Chemiresistive Electronic Nose toward Detection of Biomarkers in Exhaled Breath
Moon, Hi Gyu,Jung, Youngmo,Han, Soo Deok,Shim, Young-Seok,Shin, Beomju,Lee, Taikjin,Kim, Jin-Sang,Lee, Seok,Jun, Seong Chan,Park, Hyung-Ho,Kim, Chulki,Kang, Chong-Yun American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.32
<P>Detection of gas-phase chemicals finds a wide variety of applications, including food and beverages, fragrances, environmental monitoring, chemical and biochemical processing, medical diagnostics, and transportation. One approach for these tasks is to use arrays of highly sensitive and selective sensors as an electronic nose. Here, we present a high performance chemiresistive electronic nose (CEN) based on an array of metal oxide thin films, metal-catalyzed thin films, and nanostructured thin films. The gas sensing properties of the CEN show enhanced sensitive detection of H2S, NH3, and NO in an 80% relative humidity (RH) atmosphere similar to the composition of exhaled breath. The detection limits of the sensor elements we fabricated are in the following ranges: 534 ppt to 2.87 ppb for H2S, 4.45 to 42.29 ppb, for NH3, and 206 ppt to 2.06 ppb for NO. The enhanced sensitivity is attributed to the spillover effect by Au nanoparticles and the high porosity of villi-like nanostructures, pioviding a large surface-to-volume ratio. The remarkable selectivity based on the collection of sensor responses manifests itself in the principal component analysis (PCA). The excellent sensing performance indicates that the CEN can detect the biomarkers of H2S, NH3, and NO in exhaled breath and even distinguish them clearly in the PC:A. Our results show high potential of the CEN as an inexpensive and noninvasive diagnostic tool for halitosis, kidney disorder, and asthma.</P>
Mechanism of the Sensitivity Enhancement in TiO2 Hollow-Hemisphere Gas Sensors
( Hi Gyu Moon ),( Ho Won Jang ),( Jin Sang Kim ),( Hyung Ho Park ),( Seok Jin Yoon ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.4
We investigate the mechanism of the sensitivity enhancement in TiO2 hollow-hemisphere gas sensors. Using monolayer close-packed polystyrene microspheres as a sacrificial template, a TiO2 thin film based on a network of ordered hollow hemispheres is formed by room-temperature sputtering deposition and subsequent calcination at 550°C. A thin film gas sensor based on the TiO2 hollow hemispheres exhibits a 225% change in its resistance when exposed to 50 ppm CO at 250°C, whereas a gas sensor based on a flat TiO2 film shows an 85% change. Numerical analysis reveals that the enhancement of the gas sensitivity in the hollow-hemisphere gas sensor is simply the result of an increase in the effective surface area for the adsorption of gas molecules.
( Hi Gyu Moon ),( Ho Won Jang ),( Jin Sang Kim ),( Hyung Ho Park ),( Seok Jin Yoon ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.1
This study investigates the CO sensing properties of nanostructured TiO2 thin film gas sensors fabricated with colloidal templates using different sizes of polymer spheres. Compared to plain films, the nanostructured films show enhanced gas sensing in the form of greater sensitivity and a faster response. More interestingly, the use of colloidal templates with smaller spheres (300 nm in diameter) leads to close-packed nanostructured TiO2 thin films with very large-scale uniformity and a more pronounced improvement in CO sensing compared to the use of larger spheres (1 ㎛ in diameter). This result suggests that an understanding of the sphere size effects on the gas sensing properties of nanostructured TiO2 thin films created by colloidal templating is important in the development of these films for actual applications.
Chemiresistive Sensor Based on One-Dimensional WO3 Nanostructures as Non-Invasive Disease Monitors
( Hi Gyu Moon ),( Soo Deok Han ),( Chul Ki Kim ),( Hyung Ho Park ),( Seok Jin Yoon ) 한국센서학회 2014 센서학회지 Vol.23 No.5
In this study, a chemiresistive sensor based on one-dimensional WO3 nanostructures is presented for application in non invasive medical diagnostics. WO3 nanostructures were used as an active gas sensing layer and were deposited onto a SiO2/Si substrate using Pt interdigitated electrodes (IDEs). The IDE spacing was 5 μm and deposition was performed using RF sputter with glancing angle deposition mode. Pt IDEs fabricated by photolithography and dry etching. In comparison with thin film sensor, sensing performance of nanostructure sensor showed an enhanced response of more than 20 times when exposed to 50 ppm acetone at 400°C. Such a remarkable faster response can pave the way for a new generation of exhaled breath analyzers based on chemiresistive sensors which are less expensive, more reliable, and less complicated to be manufactured. Moreover, presented sensor technology has the potential of being used as a personalized medical diagnostics tool in the near future.
Moon, Hi Gyu,Choi, You Rim,Shim, Young-Seok,Choi, Kwon-Il,Lee, Jong-Heun,Kim, Jin-Sang,Yoon, Seok-Jin,Park, Hyung-Ho,Kang, Chong-Yun,Jang, Ho Won American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.21
<P>Self-assembled WO<SUB>3</SUB> thin film nanostructures with 1-dimensional villi-like nanofingers (VLNF) have been synthesized on the SiO<SUB>2</SUB>/Si substrate with Pt interdigitated electrodes using glancing angle deposition (GAD). Room-temperature deposition of WO<SUB>3</SUB> by GAD resulted in anisotropic nanostructures with large aspect ratio and porosity having a relative surface area, which is about 32 times larger than that of a plain WO<SUB>3</SUB> film. A WO<SUB>3</SUB> VLNF sensor shows extremely high response to nitric oxide (NO) at 200 °C in 80% of relative humidity atmosphere, while responses of the sensor to ethanol, acetone, ammonia, and carbon monoxide are negligible. Such high sensitivity and selectivity to NO are attributed to the highly efficient modualtion of potential barriers at narrow necks between individual WO<SUB>3</SUB> VLNF and the intrinsically high sensitivity of WO<SUB>3</SUB> to NO. The theoretical detection limit of the sensor for NO is expected to be as low as 88 parts per trillion (ppt). Since NO is an approved biomarker of chronic airway inflammation in asthma, unprecedentedly high response and selectivity, and ppt-level detection limit to NO under highly humid environment demonstrate the great potential of the WO<SUB>3</SUB> VLNF for use in high performance breath analyzers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-21/am402456s/production/images/medium/am-2013-02456s_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am402456s'>ACS Electronic Supporting Info</A></P>