Highly Sensitive and Selective Surface Acoustic Wave Ammonia Sensor Operated at Room Temperature with a Polyacrylic Acid Sensing Layer

Weiqiang Wang; Yuanjun Guo; Wenkai Xiong; Yongqing Fu; Ahmed Elmarakbi; Xiaotao Zu

doi:10.3390/s22176349

Highly Sensitive and Selective Surface Acoustic Wave Ammonia Sensor Operated at Room Temperature with a Polyacrylic Acid Sensing Layer

Sensors (Basel). 2022 Aug 24;22(17):6349. doi: 10.3390/s22176349.

Authors

Weiqiang Wang¹, Yuanjun Guo¹, Wenkai Xiong¹, Yongqing Fu², Ahmed Elmarakbi², Xiaotao Zu¹

Affiliations

¹ School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China.
² Faculty of Engineering & Environment, University of Northumbria, Newcastle upon Tyne, NE1 8ST, UK.

Abstract

In this study, polyacrylic acid (PAA) films were deposited onto a quartz surface acoustic wave (SAW) resonator using a spin-coating technique for ammonia sensing operated at room temperature, and the sensing mechanisms and performance were systematically studied. The oxygen-containing functional groups on the surfaces of the PAA film make it sensitive and selective to ammonia molecules, even when tested at room temperature. The ammonia molecules adsorbed by the oxygen-containing functional groups of PAA (e.g., hydroxyl and epoxy groups) increase the membrane's stiffness, which was identified as the primary mechanism leading to the positive frequency shifts. However, mass loading due to adsorption of ammonia molecules is not a major reason as it will result in a negative frequency shifts. When the PAA coated SAW sensor was exposed to ammonia with a low concentration of 500 ppb, it showed a positive frequency shift of 225 Hz, with both good repeatability and stability, as well as a good selectivity to ammonia compared with those to C₂H₅OH, H₂, HCl, H₂S, CO, NO₂, NO, and CH₃COCH₃.

Keywords: ammonia sensor; polyacrylic acid (PAA); surface acoustic wave (SAW).

Abstract

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