The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

Polymers in sensor applications

Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

Organic conjugated polymers (conducting polymers) have emerged as potentialcandidates for electrochemical sensors. Due to their straightforward preparation methods,unique properties, and stability in air, conducting polymers have been applied to energystorage, electrochemical devices, memory devices, chemical sensors, and electrocatalysts.Conducting polymers are also known to be compatible with biological molecules in aneutral aqueous solution. Thus, these are extensively used in the fabrication of accurate,fast, and inexpensive devices, such as biosensors and chemical sensors in the medicaldiagnostic laboratories. Conducting polymer-based electrochemical sensors and biosensorsplay an important role in the improvement of public health and environment because rapiddetection, high sensitivity, small size, and specificity are achievable for environmentalmonitoring and clinical diagnostics. In this review, we summarized the recent advances inconducting polymer-based electrochemical sensors, which covers chemical sensors(potentiometric, voltammetric, amperometric) and biosensors (enzyme based biosensors,immunosensors, DNA sensors).

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Electrochemical Sensors Based on Organic Conjugated Polymers

Prospects of conducting polymers in biosensors.

The polypyrrole (Ppy) incorporated with DBSA and APS was synthesized by chemical polymerization at 0 °C under atmospheric conditions. Ppy films were prepared by the dip coating method on the alumina substrate with interdigitated electrodes in order to employ the gas sensor. The electrical properties of the sensors, such as sensitivity, response and recovery time, reproducibility and long-term stability were investigated in the flow systems after various pretreatments. The electrical properties of the sensors depended on the pretreatment conditions. Soaking pretreatment resulted in a quick response and recovery time of the sensor and maintained electrical properties of the sensor for 3 months. Initial resistance of the sensor decreased with thermal treatment and this improved the stability of the sensor.

Electrical properties of polypyrrole gas sensors fabricated under various pretreatment conditions

Polypyrrole (PPy)–poly(vinyl alcohol) (PVA) composite and pure polypyrrole methanol sensors were prepared by an in situ vapor state polymerization method and their chemical structures were identified by a FT-Raman spectroscopy. The various electrical sensing behaviors of both types of sensors were systematically investigated by a flow measuring system including mass flow controller (MFC) and bubbling bottle. The incorporation of PVA into the polymer film caused a higher sensitivity than that of pure PPy sensor, while the response and recovery time and long-term stability were worse. The effect of thickness of sensing film was also investigated, and it was found that the thinner film showed higher sensitivity, which indicated that the resistance involved in sensing behavior comes from bulk resistance of sensor rather than surface resistance.

/pdf/sensing-characteristics-of-polypyrrole-poly-vinyl-alcohol-1d3d7nl506.pdf

Sensing characteristics of polypyrrole–poly(vinyl alcohol) methanol sensors prepared by in situ vapor state polymerization

Polypyrrole (PPy) and polypyrrole-poly (vinyl alcohol) (PVA) composite methanol sensors were prepared by chemical and in-situ vapor state polymerization method, respectively, and their chemical structures were identified by a FT-Raman spectroscopy. The sensing behaviors of two-type methanol gas sensors, such as sensitivity, response and recovery time, reproducibility and long-term stability were investigated by using a flow measuring system including mass flow controller (MFC), temperature controllers and bubbling bottle. The sensitivity of the sensors almost linearly increased with the increase of methanol concentration from 87ppm to 1059ppm. The sensitivity of vapor state polymerized PPy/PVA composite sensor was higher than that of chemically polymerized PPy sensor, while the response and recovery time and long-term stability were worse.

Yong-Su Hoh

Papers

Electrical properties of polypyrrole gas sensors fabricated under various pretreatment conditions

Sensing characteristics of polypyrrole–poly(vinyl alcohol) methanol sensors prepared by in situ vapor state polymerization

Polypyrrole-Based Methanol Sensors Prepared by Chemical and Vapor State Polymerization