Byoung Sam Kang

Carbon nanotube films for room temperature hydrogen sensing.

Thin, uniform, single-walled carbon nanotube films, made by a simple filtration process, subsequently coated with palladium, are shown to be promising detectors of hydrogen. The films detected hydrogen with relative responses of 20% at 100 ppm and 40% at 500 ppm concentrations. Most of the initial film conductance was recovered within 30 s by exposing the samples to air. This quick and easy recoverability make the Pd-coated nanotubes suitable for practical applications in room temperature hydrogen sensing while consuming only approximately 0.25 mW power. The film fabrication process provides highly reproducible control over the film thickness; an important ingredient for commercial production. In the course of this research strong evidence was obtained indicating that sputter deposition of metal onto the nanotubes, even under very low power, short exposure time conditions, does damage to the nanotubes.

Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices.

In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs). ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO2 and C2H4 using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application.

Aluminum Gallium Nitride (GaN)/GaN High Electron Mobility Transistor-Based Sensors for Glucose Detection in Exhaled Breath Condensate

Background: Immobilized aluminum gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs) have shown great potential in the areas of pH, chloride ion, and glucose detection in exhaled breath condensate (EBC). HEMT sensors can be integrated into a wireless data transmission system that allows for remote monitoring. This technology offers the possibility of using AlGaN/GaN HEMTs for extended investigations of airway pathology of detecting glucose in EBC without the need for clinical visits. Methods: HEMT structures, consisting of a 3-μm-thick undoped GaN buffer, 30-Å-thick Al03Ga07N spacer, and 220-Å-thick silicon-doped Al03Ga07N cap layer, were used for fabricating the HEMT sensors. The gate area of the pH, chloride ion, and glucose detection was immobilized with scandium oxide (Sc2O3), silver chloride (AgCl) thin film, and zinc oxide (ZnO) nanorods, respectively. Results: The Sc2O3-gated sensor could detect the pH of solutions ranging from 3 to 10 with a resolution of ∼0.1 pH. A chloride ion detection limit of 10−8 M was achievedt with a HEMT sensor immobilized with the AgCl thin film. The drain-source current of the ZnO nanorod-gated AlGaN/GaN HEMT sensor immobilized with glucose oxidase showed a rapid response of less than 5 seconds when the sensor was exposed to the target glucose in a buffer with a pH value of 7.4. The sensor could detect a wide range of concentrations from 0.5 nM to 125 μM. Conclusion: There is great promise for using HEMT-based sensors to enhance the detection sensitivity for glucose detection in EBC. Depending on the immobilized material, HEMT-based sensors can be used for sensingt different materials. These electronic detection approaches with rapid response and good repeatability show potential for the investigation of airway pathology. The devices can also be integrated into a wireless data transmission system for remote monitoring applications. This sensor technology could use the exhaled breath condensate to measure the glucose concentration for diabetic applications.

AlGaN/GaN High Electron Mobility Transistor Based Sensors for Bio-Applications

Chemical sensors have gained in importance in the past decade for applications that include homeland security, medical and environmental monitoring and also food safety. A desirable goal is the ability to simultaneously analyze a wide variety of environmental and biological gases and liquids in the field and to be able to selectively detect a target analyte with high specificity and sensitivity. In the area of detection of medical biomarkers, many different methods, including enzyme-linked immunsorbent assay (ELISA), particle-based flow cytometric assays, electrochemical measurements based on impedance and capacitance, electrical measurement of microcantilever resonant frequency change, and conductance measurement of semiconductor nanostructures. gas chromatography (GC), ion chromatography, high density peptide arrays, laser scanning quantitiative analysis, chemiluminescence, selected ion flow tube (SIFT), nanomechanical cantilevers, bead-based suspension microarrays, magnetic biosensors and mass spectrometry (MS) have been employed (Burlingame, Boyd and Gaskell 1996, Jackson and Chen 1996, Anderson, Bowden and Pickup 1996, Chen et al. 2003, Li et al. 2005, Zhang et al. 2006, Huber, Lang and Gerber 2008, Sandhu 2007, Zheng et al. 2005b). Depending on the sample condition, these methods may show variable results in terms of sensitivity for some applications and may not meet the requirements for a handheld biosensor. For homeland security applications, reliable detection of biological agents in the field and in real time is challenging. During the anthrax attack on the World Bank in 2002, field tests showed 1200 workers to be positive, and all were sent home. 100 workers were provided antibiotics. However, confirmatory testing showed zero positives. False positives and false negatives can result due to very low volumes of samples available for testing and poor device sensitivities. Toxins such as ricin, botulinum toxin or enterotoxin B are environmentally stable, can be mass-produced and do not need advanced technologies for production and dispersal. The threat of these toxins is real. This is evident from the recent ricin detection from White House mail facilities and a US senator’s office. Terrorists have already attempted to use botulinum toxin as a bio-weapon. Aerosols were dispersed at multiple sites in Tokyo, and at US military installations in Japan on at least 3 occasions between 1990 and 1995 by the Japanese cult Aum Shinrikyo (Greenfield et al. 2002). Four of the countries listed by the US government as “state sponsors of terrorism” (Iran, Iraq, North Korea, and Syria) (Greenfield et al. 2002) have developed, or are believed to be developing,

Rapid Electrical Detection of Hg(II) Ions with AlGaN/GaN High Electron Mobility Transistors

Bare Au gated and thioglycolic acid functionalized Au-gated AlGaN/GaN high electron mobility transistors HEMTs were used to detect mercury II ions. Fast detection of less than 5 s was achieved for thioglycolic acid functionalized sensors. This is the shortest response time ever reported for mercury detection. Thioglycolic acid functionalized Au-gated AlGaN/GaN HEMT based sensors showed 2.5 times larger response than bare Au-gated based sensors. The sensors were able to detect mercury II ion concentration as low as 10−7M. The sensors showed an excellent sensing selectivity of more than 100 for detecting mercury ions over sodium or magnesium ions. The dimensions of the active area of the sensor and the entire sensor chip are 50 50 m2 and 1 5 mm2, respectively. Therefore, portable, fast response, and wireless based heavy metal ion detectors can be realized with AlGaN/GaN HEMT based sensors.

c-erbB-2 Sensing Using AlGaN/GaN High Electron Mobility Transistors For Breast Cancer Detection

Antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect c-erbB-2, a breast cancer marker. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 seconds when target c-erbB-2 antigen in a buffer at clinically relevant concentrations was added to the antibody-immobilized surface. We could detect a range of concentrations from to 16.7 μg/ml to 0.25 μg/ml. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN/GaN HEMTs for breast cancer screening.