{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,11]],"date-time":"2025-11-11T13:48:09Z","timestamp":1762868889249,"version":"build-2065373602"},"reference-count":37,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2022,8,24]],"date-time":"2022-08-24T00:00:00Z","timestamp":1661299200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Fundamental Research Funds for the Central Universities","award":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"],"award-info":[{"award-number":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"]}]},{"name":"Engineering Physics and Science Research Council of UK","award":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"],"award-info":[{"award-number":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"]}]},{"name":"International Exchange Grant","award":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"],"award-info":[{"award-number":["A03018023801119","EPSRC EP\/P018998\/1","IEC\/NSFC\/201078"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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\u2019s 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.<\/jats:p>","DOI":"10.3390\/s22176349","type":"journal-article","created":{"date-parts":[[2022,8,24]],"date-time":"2022-08-24T02:55:34Z","timestamp":1661309734000},"page":"6349","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Highly Sensitive and Selective Surface Acoustic Wave Ammonia Sensor Operated at Room Temperature with a Polyacrylic Acid Sensing Layer"],"prefix":"10.3390","volume":"22","author":[{"given":"Weiqiang","family":"Wang","sequence":"first","affiliation":[{"name":"School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China"}]},{"given":"Yuanjun","family":"Guo","sequence":"additional","affiliation":[{"name":"School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China"}]},{"given":"Wenkai","family":"Xiong","sequence":"additional","affiliation":[{"name":"School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9797-4036","authenticated-orcid":false,"given":"Yongqing","family":"Fu","sequence":"additional","affiliation":[{"name":"Faculty of Engineering & Environment, University of Northumbria, Newcastle upon Tyne, NE1 8ST, UK"}]},{"given":"Ahmed","family":"Elmarakbi","sequence":"additional","affiliation":[{"name":"Faculty of Engineering & Environment, University of Northumbria, Newcastle upon Tyne, NE1 8ST, UK"}]},{"given":"Xiaotao","family":"Zu","sequence":"additional","affiliation":[{"name":"School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China"}]}],"member":"1968","published-online":{"date-parts":[[2022,8,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"5469","DOI":"10.3390\/s100605469","article-title":"Metal oxide semi-conductor gas sensors in environmental monitoring","volume":"10","author":"Fine","year":"2010","journal-title":"Sensors"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1016\/j.snb.2014.04.041","article-title":"Flexible H2S sensor based on gold modified polycarbazole films","volume":"200","author":"Joshi","year":"2014","journal-title":"Sens. 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