Ultrasensitive NOX Detection in Simulated Exhaled Air: Enhanced Sensing via Alumina Modification of In-Situ Grown WO3 Nanoblocks

Suhaib Alam; Mohammad Shaad Ansari; Avishek Banik; Rafat Ali; Sandeep Verma; Mohammad Qureshi

doi:10.1002/asia.201900699

Ultrasensitive NO_X Detection in Simulated Exhaled Air: Enhanced Sensing via Alumina Modification of In-Situ Grown WO₃ Nanoblocks

Chem Asian J. 2019 Dec 13;14(24):4673-4680. doi: 10.1002/asia.201900699. Epub 2019 Aug 27.

Authors

Suhaib Alam¹, Mohammad Shaad Ansari¹, Avishek Banik¹, Rafat Ali², Sandeep Verma², Mohammad Qureshi¹

Affiliations

¹ Department of Chemistry, Indian Institute of Technology, Guwahati, Assam, 781039, India.
² Department of Chemistry and Centre for Nanoscience, Indian Institute of Technology, Kanpur, U.P, 208016, India.

PMID: 31420935
DOI: 10.1002/asia.201900699

Abstract

Seedless growth of vertically aligned nanostructures, which can induce smoother transport and minimize Ohmic contact between substrate and semiconductor, can be fabricated by in situ growth utilizing modified hydrothermal methods. Such devices can be useful in designing non-invasive ultrasensitive hand-held sensors for diagnostic identification of volatile organic compounds (VOCs) in exhaled air, offering pain-free and easier detection of long-term diseases such as asthma. In the present work, WO₃ nanoblocks, with a high surface area and porosity, have been grown directly over transparent conducting oxide to minimize Ohmic resistance, facilitating smoother electron transfer and enhanced current response. Further modification with porous alumina (γ-Al₂ O₃ ), by electrodeposition, resulted in the selective and ultrasensitive detection of NO_X in simulated exhaled air. Crystal phase purity of as-fabricated pristine as well modified samples is validated with X-ray diffraction analysis. Morphological and microstructural analyses reveal the successful deposition of porous alumina over the surface of WO₃ . Improved surface area and porosity is presented by porous alumina in the modified WO₃ device, suggesting more active sites for the gas molecules to get adsorbed and diffuse through the pores. Oxygen vacancies, which are detrimental in the transport phenomenon in the presented sensors, have been studied using X-ray photoelectron spectroscopic (XPS) analysis. Gas sensing studies have been performed by fabricating chemiresistor devices based on bare WO₃ and Al₂ O₃ -modified WO₃ . The higher sensitivity for NO_X gas in case of γ-Al₂ O₃ -modified WO₃ based devices, as compared to bare WO₃ -based devices, is attributed to the better surface area and charge transport kinetics. The presented device strategy offers crucial understanding in the design and development of non-invasive, hand-held devices for NO gas present in the human breath, with potential application in medical diagnostics.

Keywords: Asthma; Nitrogen Oxides; Non-invasive; Simulated Exhaled Breath and Chemiresistor Device; Volatile Organic Compounds (VOCs).

Abstract

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