{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,23]],"date-time":"2026-09-23T04:52:24Z","timestamp":1790139144276,"version":"4.0.1"},"reference-count":60,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2025,4,24]],"date-time":"2025-04-24T00:00:00Z","timestamp":1745452800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Stavros Niarchos Foundation"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The objective of this study is the fabrication of sensors which can detect modifications in CO2 concentrations at room temperature, thus indicating the quality or microbial spoilage of food products when incorporated into food packaging. ZnO nanostructures are known for their ability to detect organic gases; however, their effectiveness is limited to high temperatures (greater than 200 \u00b0C). To overcome this limitation, sodium (Na) doping is investigated as a way to enhance the sensing properties of ZnO films and lower the working temperature. In this study, undoped and Na-doped ZnO thin films were developed via the sol-gel method with different Na percentages (2.5, 5 and 7.5%) and were deposited via spin coating. The crystal structure, the morphology, and the surface topography of the developed films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), respectively. Furthermore, the response to CO2 was measured by varying its concentration up to 500 ppm at room temperature. All the developed films presented the characteristic diffraction peaks of the ZnO wurtzite hexagonal crystal structure. SEM revealed that the films consisted of densely packed grains, with an average particle size of 58 nm. Na doping increased the film thickness but reduced the surface roughness. Finally, the developed sensors demonstrated very good CO2 sensing properties, with the 2.5% Na-doped sensor having an enhanced sensing performance concerning sensitivity, response, and recovery times. This leads to the conclusion that Na-doped ZnO sensors could be used for the detection of microbial spoilage in food products at room temperature, making them suitable for smart food packaging applications.<\/jats:p>","DOI":"10.3390\/s25092705","type":"journal-article","created":{"date-parts":[[2025,4,24]],"date-time":"2025-04-24T10:17:16Z","timestamp":1745489836000},"page":"2705","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Fabrication of ZnO Thin Films Doped with Na at Different Percentages for Sensing CO2 in Small Quantities at Room Temperature"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9296-0548","authenticated-orcid":false,"given":"Marina","family":"Stramarkou","sequence":"first","affiliation":[{"name":"School of Chemical Engineering, National Technical University of Athens (NTUA), 15772 Athens, Greece"},{"name":"Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research (NCSR) \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5713-8252","authenticated-orcid":false,"given":"Achilleas","family":"Bardakas","sequence":"additional","affiliation":[{"name":"Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research (NCSR) \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Magdalini","family":"Krokida","sequence":"additional","affiliation":[{"name":"School of Chemical Engineering, National Technical University of Athens (NTUA), 15772 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0549-2780","authenticated-orcid":false,"given":"Christos","family":"Tsamis","sequence":"additional","affiliation":[{"name":"Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research (NCSR) \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,4,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"de C\u00e1ssia Martins Salom\u00e3o, B. 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