Int. Journal of Electrical & Electronics Engg.
Vol. 2, Spl. Issue 1 (2015)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
Carbon Nanotubes Based Sensor for Detection of Traces of Gas Molecules- A Review 1
Arvind Kumar, 2Jaspreet Kaur Rajput, 3Sukhvir Kaur 1, Department of ECE,UIET Panjab University, Chandigarh 160025 2, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar 144011 Abstract- In this review paper, we discuss various gas sensors based on technique and sensing materials used in there fabrication. Various sensors are designed making use of salient features of carbon nanotubes and its electrical, mechanical, and electromechanical properties. Effect of using nano-composites on sensitivity and selectivity of gas sensor have been studied.
While some commercial products for detecting trace energetic chemicals including explosives are now available, the need of highly sensitive and fast detection methods is continuously increasing and the research into alternative technologies continues at a pace. This is a result of the fact that detecting trace chemicals in a complex environment still remains a significant technological challenge because of the extremely low concentrations of the chemicals in solutions or low partial pressures in the air. For example, the partial pressure of 2,4,6-trinitrotoluene (TNT) is a few parts per billion (ppb) at room temperature and in the subpart per trillion range in the air above a buried mine. Nowadays, electronic nose has become a powerful tool to detect even the traces of explosive materials [2]. To address this challenge, various detection methods with potential to achieve low limit of detection (LOD) are being investigated for trace chemical detection, such as electro-chemical sensors, biosensor, fluorescence and Raman-based optical methods, mass spectrometry (MS), ion mobility spectrometry (IMS), and sensors based on nano and microfabrication technologies. Electrochemical sensors provide some selectivity but suffer from limited sensitivity and require mobile electrolytes, which may cause stability issues and delayed response time. In addition, electrodes can be easily fouled, and interfering problems may occur as some interferents are electrochemically active. Nanomaterials, e.g., carbon nanotubes (CNTs) and nanowires, have been employed to construct electrochemical sensors for explosive detections [3]. CNTs applications include CNTs field-effect transistors or resistors and CNTs modified glassy carbon electrodes. More recently, CNTs have been employed in explosive sensors by exploiting passive functions rather than transduction, such as enhanced Raman scattering and preconcentration of target samples. LODs down to the ppb level have been achieved for TNT detection by exploiting the extremely large surface-to-volume ratio. Despite high sensitivity, significant challenges such as low selectivity, low signal-to-noise ratio (SNR), long recovery times, interference, and device fabrication difficulties still remain to be addressed [4-6].
Index Terms – Carbon Nanotubes (CNTs), Electrochemical sensor (E-nose), sensors.
I. INTRODUCTION Sensors are the devices which convert any form of energy or any physical parameters into electrical signals/measurable signals. Pressure sensor, gas sensor, humidity sensor, chemical sensors are some few examples of sensors available in the market. Gas sensors are the devices that are used to detect gas molecules in atmosphere which may cause harm to our health. There are more than one hundred types of military and civilian explosives and around twenty commonly used drugs. A number of characteristics can be used for the detection of gas molecules [1]: ˗ Geometry (the presence a metallic detonator can be detected using image shape analysis), ˗ Material density (explosive material is denser than most organic materials), ˗ Elemental composition (e.g. vapor emission analysis can be used to detect them), ˗ Vapor emissions (e.g. nitrogen or its compounds can be detected in a vapor sample). A. Detection methods Vapor detection methods are used to measure traces of characteristic volatile compounds that evaporate from the explosive and other gas molecules [1]. However, the concentration of explosive vapors inside the sensors is many orders of magnitude lower than the pressure of saturated vapor on the explosives surface. Vapors and traces are commonly detected by means of: - Electronic/chemical sensors, - Optical sensors, - Biosensors.. A new type of pressure sensor propose approaches for improving sensitivity, selectivity and size. The most powerful pressure sensor contains microelectronics circuits, which enable to install a digital pressure gauge just in sensor and software control starting of different electronic regulations in according to the measured values. Special pressure sensors present sensors for explosive environment. B. Electrochemical sensor (E-nose) 133
C. CNTs as sensing material
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Detection of trace explosives is still a challenging task because of the extremely low vapor concentrations. Current explosive/gas sensors are mainly categorized into two modes of operation; chemical type operating by gas adsorption and physical type using ionization method. Chemical type conductivity-based explosive detectors are bulky, they require high operating temperatures and have slow response time. Moreover most of them are capable of
NITTTR, Chandigarh
EDIT-2015