{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,8]],"date-time":"2026-05-08T03:34:40Z","timestamp":1778211280684,"version":"3.51.4"},"reference-count":47,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2020,1,15]],"date-time":"2020-01-15T00:00:00Z","timestamp":1579046400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic complexes. In contrast, we propose a novel route of optical oxygen sensing by fluorescence-based quenching of oxygen. We hereby developed for the first time a set of multi-emissive purely organic emitters. These were produced through a one-pot hydrothermal synthesis using p-phenylenediamine (PPD) and urea as starting materials. The origin of the multi-emission has been ascribed to the diversity of chemical structures produced as a result of oxidative oligomerization of PPD. A Bandrowski\u2019s base (BB, i.e., trimer of PPD) is reported as the main component at reaction times higher than 8 h. This indication was confirmed by electrospray-ionization quadrupole time-of-flight (ESI-QTOF) and liquid chromatography-mass spectrometry (LC-MS) analysis. Once the emitters are embedded within a high molecular weight poly (vinyl alcohol) matrix, the intensities of all three emission centers exhibit a non-linear quenching provoked by oxygen within the range of 0\u20138 kPa. The detection limit of the emission centers are 0.89 kPa, 0.67 kPa and 0.75 kPa, respectively. This oxygen-dependent change in fluorescence emission is reversible (up to three tested 0\u201321% O2 cycles) and reproducible with negligible cross-interference to humidity. The cost-effectiveness, metal-free formulation, cross-referencing between each single emission center and the relevant oxygen range are all appealing features, making these sensors promising for the detection of oxygen, e.g., in food packaged products.<\/jats:p>","DOI":"10.3390\/s20020477","type":"journal-article","created":{"date-parts":[[2020,1,15]],"date-time":"2020-01-15T11:50:28Z","timestamp":1579089028000},"page":"477","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Reversible Oxygen Sensing Based on Multi-Emission Fluorescence Quenching"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2749-8473","authenticated-orcid":false,"given":"Efe","family":"Armagan","sequence":"first","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"},{"name":"Institute of Materials, Ecole Polytechnique F\u00e9d\u00e9rale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland"}]},{"given":"Shankar","family":"Thiyagarajan","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6555-2768","authenticated-orcid":false,"given":"Kongchang","family":"Wei","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"}]},{"given":"Akin","family":"Gursoy","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"},{"name":"Institute of Materials, Ecole Polytechnique F\u00e9d\u00e9rale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3889-7816","authenticated-orcid":false,"given":"Giuseppino","family":"Fortunato","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9491-1010","authenticated-orcid":false,"given":"Esther","family":"Amstad","sequence":"additional","affiliation":[{"name":"Institute of Materials, Ecole Polytechnique F\u00e9d\u00e9rale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0946-682X","authenticated-orcid":false,"given":"Ren\u00e9 Michel","family":"Rossi","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3903-4972","authenticated-orcid":false,"given":"Claudio","family":"Toncelli","sequence":"additional","affiliation":[{"name":"Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland"}]}],"member":"1968","published-online":{"date-parts":[[2020,1,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3666","DOI":"10.1039\/C4CS00039K","article-title":"Optical methods for sensing and imaging oxygen: Materials, spectroscopies and applications","volume":"43","author":"Wang","year":"2014","journal-title":"Chem. 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