The paper presents a substantial review of the work done on the design and development of different types of gas sensors using Carbon Nanotubes. The fundamental techniques of preparation of Carbon Nanotubes have also been reported here. The variety of sensors, their detection processes of a range of gases including NO2, H2S, C2H5OH, and others have been described here. Single-Walled and Multi-Walled Carbon Nanotubes in their pristine and amalgamated forms has been used and to develop a range of sensing devices. It also presents a comparative study on each gas giving the fundamental parameters like the limit of detection, the range of concentration and response time to differentiate their capability regarding the materials used to fabrication them to detect the gases. Finally, the challenges related to the currently available Carbon Nanotubes-based gas sensors, their associated remedial actions and some of the possible opportunities for future work are elucidated in the paper.

Carbon nanotubes and its gas-sensing applications: A review

Background Fresh fruit are important for a healthy diet, however, their shelf-life can be shortened because of ethylene, a key phytohormone associated with the ripening process. Therefore, detecting ethylene concentration on trace level and regulating its activity by safe and effective approaches are of paramount importance in extending postharvest shelf-life and controlling maturity of fruit. Scope and approach In this review, ethylene detection technologies as well as ethylene regulating strategies are discussed, aiming to develop more innovative and effective approaches. Effects of ethylene on quality and shelf-life of fruit are presented. Ethylene detection and monitoring technologies available such as gas chromatography, electrochemical, optical, chemical methods, especially novel methods such as those based on colorimetric, luminescence, metal-organic frameworks, organic field effect transistors and surface enhanced Raman spectroscopy are described. In addition, shelf-life extending technologies for ethylene control, removal or inhibition such as suppressing ethylene synthesis, scavenging or oxidizing or adsorbing ethylene, and blocking ethylene receptor are summarized. Finally, future perspectives on developing strategies that can simultaneously satisfy the requirements of sensitivity, rapidness and on-line for wide utilization in ethylene monitoring of fresh products are also given. Key findings and conclusions It is expected that miniature and sensitive ethylene detection techniques combined with feasible ethylene control methods should be an effective solution for fruit quality maintenance and shelf-life extension. However, each type of sensors and ethylene control strategies currently available has their own advantages and limitations. Therefore, attempts should be made to exploit more effective ethylene detection and controlling technologies.

Recent advances in detecting and regulating ethylene concentrations for shelf-life extension and maturity control of fruit: A review

Polymers Chemistry And Physics Of Modern Materials

Plant hormones are a group of naturally occurring, low-abundance organic compounds that influence physiological processes in plants. Our knowledge of the distribution profiles of phytohormones in plant organs, tissues, and cells is still incomplete, but advances in mass spectrometry have enabled significant progress in tissue- and cell-type-specific analyses of phytohormones over the last decade. Mass spectrometry is able to simultaneously identify and quantify hormones and their related substances. Biosensors, on the other hand, offer continuous monitoring; can visualize local distributions and real-time quantification; and, in the case of genetically encoded biosensors, are noninvasive. Thus, biosensors offer additional, complementary technologies for determining temporal and spatial changes in phytohormone concentrations. In this review, we focus on recent advances in mass spectrometry–based quantification, describe monitoring systems based on biosensors, and discuss validations of the various methods ...

Zooming In on Plant Hormone Analysis: Tissue- and Cell-Specific Approaches

Ag decorated WO3 sensor for the detection of sub-ppm level NO2 concentration in air

Purpose




The purpose of this paper was to develop a chemo-resistive sensor based on TiO2–WO3 composite material to detect and estimate ethylene released from the fruit ripening process to ensure food safety.




Design/methodology/approach




The ethylene sensor has been fabricated using TiO2–WO3 composite material through the sol-gel method.




Findings




The sensitivity of the sensor obtained using the pre-calibrated ethylene is found to be 46.2 per cent at 200 ppm ethylene concentration, and the proposed sensor could measure 8 ppm as the lowest concentration.




Originality/value




The sensor was tested for continuous ethylene detection during natural ripening of fruits and hence is useful for ensuring food safety through discrimination of the type of fruit ripening. A TiO2–WO3 composite ethylene sensor is developed for the first time.

Ethylene detection using TiO2–WO3 composite sensor for fruit ripening applications

An infrared based sensor system for the detection of ethylene for the discrimination of fruit ripening

We report here a prototype laboratory setup for detecting ethylene (C2H4) in ppm level employing a sensor made of multiwalled carbon nanotubes of 40 nm average tube diameter. The proposed reversible chemoresistive ethylene sensor is fabricated using Kapton as the substrate onto which carbon nanotubes are coated using thick film technology. IDT silver electrodes are printed using piezo head based ink-jet printing technology. The increases in electrical resistance of the sensor element are measured on exposure to ethylene for different ethylene concentrations using a potentiostat and data acquisition system. The increase in resistance of the calibrated sensor element on exposure to ethylene (analyte) is about 18.4% at room temperature for 50 ppm ethylene concentration. This change is reversible. Our sensor element exhibits a better performance than those reported earlier (1.8%) and it has got the rise and fall time of 10 s and 60 s, respectively. It could be used for testing the ripening of fruits.

https://downloads.hindawi.com/journals/js/2014/395035.pdf

Development of Prototype Laboratory Setup for Selective Detection of Ethylene Based on Multiwalled Carbon Nanotubes

Development of automatic voice activated low cost wheelchair using intelligent standalone controlling system and Interfaces (Embedded LabVIEW and Compact Reconfigurable Input/Output FPGA Card-cRIO-9074) for physically impaired people is presented in this paper. Various interfaces to control the powered wheelchair were proposed in the past since the voice is the most natural communication ways for person so our study pays more attention to speech recognition. The voice commands produced by the user are captured and processed by the intelligent system. The system is integrated with Ultrasonic sensor and IR sensor for obstacle detection and path finding.

Development of low cost automatic wheelchair controlled by oral commands using standalone controlling system

This work encompasses the various laboratory-based and portable methods evolved in recent times for sensitive and selective detection of ethylene for fruit-ripening application. The role of ethylene in natural and artificial fruit ripening and the associated health hazards are well known. So there is a growing need for ethylene detection. This paper aims to highlight potential methods developed for ethylene detection by various researchers, including ours. Intense efforts by various researchers have been on since 2014 for societal benefits.,The paper focuses on types of sensors, fabrication methods and signal conditioning circuits for ethylene detection in ppm levels for various applications. The authors have already designed, developed a laboratory-based set-up belonging to the electrochemical and optical methods for detection of ethylene.,The authors have developed a carbon nanotube (CNT)-based chemical sensor whose performance is higher than the reported sensor in terms of material, sensitivity and response, the sensor element being multi-walled carbon nanotube (MWCNT) in comparison to single-walled carbon nanotube (SWCNT). Also the authors have developed infrared (IR)-based physical sensor for the first time based on the strong IR absorption of ethylene at 10.6 µm. These methods have been compared with literature based on comparable parameters. The review highlights the potential possibilities for development of portable device for field applications.,The authors have reported new chemical and physical sensors for ethylene detection and quantification. It is demonstrated that it could be used for fruit-ripening applications A comparison of reported methods and potential opportunities is discussed.

J. Kathirvelan

Papers

Ethylene detection using TiO2–WO3 composite sensor for fruit ripening applications

An infrared based sensor system for the detection of ethylene for the discrimination of fruit ripening

Development of Prototype Laboratory Setup for Selective Detection of Ethylene Based on Multiwalled Carbon Nanotubes

Development of low cost automatic wheelchair controlled by oral commands using standalone controlling system

Review on sensitive and selective ethylene detection methods for fruit ripening application