{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,7]],"date-time":"2026-03-07T19:00:51Z","timestamp":1772910051575,"version":"3.50.1"},"reference-count":32,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2014,2,27]],"date-time":"2014-02-27T00:00:00Z","timestamp":1393459200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A universal pH indicator is used to fabricate a fiber optic ammonia sensor.  The advantage of this pH indicator is that it exhibits sensitivity to ammonia over a broad wavelength range. This provides a differential response, with a valley around 500 nm and a peak around 650 nm, which allows us to perform ratiometric measurements. The ratiometric measurements provide not only an enhanced signal, but can also eliminate any external disturbance due to humidity or temperature fluctuations. In addition, the indicator is embedded in a hydrophobic and gas permeable polyurethane film named Tecoflex\u00ae. The film provides additional advantages to the sensor, such as operation in dry environments, efficient transport of the element to be measured to the sensitive area of the sensor, and prevent leakage or detachment of the indicator. The combination of the universal pH indicator and Tecoflex\u00ae film provides a reliable and robust fiber optic ammonia sensor.<\/jats:p>","DOI":"10.3390\/s140304060","type":"journal-article","created":{"date-parts":[[2014,2,27]],"date-time":"2014-02-27T11:05:59Z","timestamp":1393499159000},"page":"4060-4073","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":36,"title":["A Fiber Optic Ammonia Sensor Using a Universal pH Indicator"],"prefix":"10.3390","volume":"14","author":[{"given":"Adolfo","family":"Rodr\u00edguez","sequence":"first","affiliation":[{"name":"Fiber and Integrated Optics Laboratory, Electronics Engineering Department,  UAM Reynosa Rodhe, Universidad Aut\u00f3noma de Tamaulipas, Carr. Reynosa-San Fernando S\/N, Reynosa, Tamaulipas 88779, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6601-5449","authenticated-orcid":false,"given":"Carlos","family":"Zamarre\u00f1o","sequence":"additional","affiliation":[{"name":"Departamento de Ingenier\u00eda El\u00e9ctrica y Electr\u00f3nica, Universidad P\u00fablica de Navarra, Edif. Los Tejos, Campus Arrosadia, Pamplona Espa\u00f1a 31006, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2229-6178","authenticated-orcid":false,"given":"Ignacio","family":"Mat\u00edas","sequence":"additional","affiliation":[{"name":"Departamento de Ingenier\u00eda El\u00e9ctrica y Electr\u00f3nica, Universidad P\u00fablica de Navarra, Edif. Los Tejos, Campus Arrosadia, Pamplona Espa\u00f1a 31006, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3311-0834","authenticated-orcid":false,"given":"Francisco.","family":"Arregui","sequence":"additional","affiliation":[{"name":"Departamento de Ingenier\u00eda El\u00e9ctrica y Electr\u00f3nica, Universidad P\u00fablica de Navarra, Edif. Los Tejos, Campus Arrosadia, Pamplona Espa\u00f1a 31006, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Rene","family":"Cruz","sequence":"additional","affiliation":[{"name":"Fiber and Integrated Optics Laboratory, Electronics Engineering Department,  UAM Reynosa Rodhe, Universidad Aut\u00f3noma de Tamaulipas, Carr. Reynosa-San Fernando S\/N, Reynosa, Tamaulipas 88779, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Daniel.","family":"May-Arrioja","sequence":"additional","affiliation":[{"name":"Fiber and Integrated Optics Laboratory, Electronics Engineering Department,  UAM Reynosa Rodhe, Universidad Aut\u00f3noma de Tamaulipas, Carr. Reynosa-San Fernando S\/N, Reynosa, Tamaulipas 88779, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,2,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"666","DOI":"10.1016\/j.snb.2004.11.054","article-title":"Ammonia sensors and their applications\u2013A review","volume":"107","author":"Timmer","year":"2005","journal-title":"Sen. Actuators B Chem."},{"key":"ref_2","unstructured":"Ammonia (NH3) CAS 7664\u20137 UN 2672 (Between 12% and 44% solution), UN 2073 (>44% solution), UN 1005 (anhydrous gas or >50% solution). 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