{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,14]],"date-time":"2026-01-14T16:46:30Z","timestamp":1768409190175,"version":"3.49.0"},"reference-count":33,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2020,10,27]],"date-time":"2020-10-27T00:00:00Z","timestamp":1603756800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000266","name":"Engineering and Physical Sciences Research Council","doi-asserted-by":"publisher","award":["EP\/K03197X\/1 and EP\/R005257\/1"],"award-info":[{"award-number":["EP\/K03197X\/1 and EP\/R005257\/1"]}],"id":[{"id":"10.13039\/501100000266","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100009767","name":"Heriot-Watt University","doi-asserted-by":"publisher","award":["James-Watt Scholarship"],"award-info":[{"award-number":["James-Watt Scholarship"]}],"id":[{"id":"10.13039\/100009767","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Numerous optodes, with fluorophores as the chemical sensing element and optical fibres for light delivery and collection, have been fabricated for minimally invasive endoscopic measurements of key physiological parameters such as pH. These flexible miniaturised optodes have typically attempted to maximize signal-to-noise through the application of high concentrations of fluorophores. We show that high-density attachment of carboxyfluorescein onto silica microspheres, the sensing elements, results in fluorescence energy transfer, manifesting as reduced fluorescence intensity and lifetime in addition to spectral changes. We demonstrate that the change in fluorescence intensity of carboxyfluorescein with pH in this \u201chigh-density\u201d regime is opposite to that normally observed, with complex variations in fluorescent lifetime across the emission spectra of coupled fluorophores. Improved understanding of such highly loaded sensor beads is important because it leads to large increases in photostability and will aid the development of compact fibre probes, suitable for clinical applications. The time-resolved spectral measurement techniques presented here can be further applied to similar studies of other optodes.<\/jats:p>","DOI":"10.3390\/s20216115","type":"journal-article","created":{"date-parts":[[2020,10,29]],"date-time":"2020-10-29T21:21:00Z","timestamp":1604006460000},"page":"6115","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["Time-Resolved Spectroscopy of Fluorescence Quenching in Optical Fibre-Based pH Sensors"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8387-9641","authenticated-orcid":false,"given":"Katjana","family":"Ehrlich","sequence":"first","affiliation":[{"name":"Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK"},{"name":"EPSRC Proteus IRC Hub, Centre for Inflammation Research, Queen\u2019s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4655-9905","authenticated-orcid":false,"given":"Tushar R.","family":"Choudhary","sequence":"additional","affiliation":[{"name":"EPSRC Proteus IRC Hub, Centre for Inflammation Research, Queen\u2019s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK"},{"name":"Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering &amp; Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Muhammed","family":"Ucuncu","sequence":"additional","affiliation":[{"name":"School of Chemistry, EaStChem, University of Edinburgh, Joseph Black Building, West Mains Road, Edinburgh EH9 3FF, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1373-8675","authenticated-orcid":false,"given":"Alicia","family":"Megia-Fernandez","sequence":"additional","affiliation":[{"name":"School of Chemistry, EaStChem, University of Edinburgh, Joseph Black Building, West Mains Road, Edinburgh EH9 3FF, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kerrianne","family":"Harrington","sequence":"additional","affiliation":[{"name":"Centre for Photonics and Photonic Materials, University of Bath, Claverton Down, Bath BA27AY, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4430-2257","authenticated-orcid":false,"given":"Harry A. C.","family":"Wood","sequence":"additional","affiliation":[{"name":"Centre for Photonics and Photonic Materials, University of Bath, Claverton Down, Bath BA27AY, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1831-859X","authenticated-orcid":false,"given":"Fei","family":"Yu","sequence":"additional","affiliation":[{"name":"Centre for Photonics and Photonic Materials, University of Bath, Claverton Down, Bath BA27AY, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Debaditya","family":"Choudhury","sequence":"additional","affiliation":[{"name":"Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kev","family":"Dhaliwal","sequence":"additional","affiliation":[{"name":"EPSRC Proteus IRC Hub, Centre for Inflammation Research, Queen\u2019s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mark","family":"Bradley","sequence":"additional","affiliation":[{"name":"EPSRC Proteus IRC Hub, Centre for Inflammation Research, Queen\u2019s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK"},{"name":"School of Chemistry, EaStChem, University of Edinburgh, Joseph Black Building, West Mains Road, Edinburgh EH9 3FF, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7432-0312","authenticated-orcid":false,"given":"Michael G.","family":"Tanner","sequence":"additional","affiliation":[{"name":"Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK"},{"name":"EPSRC Proteus IRC Hub, Centre for Inflammation Research, Queen\u2019s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"355","DOI":"10.1088\/1464-4258\/3\/5\/307","article-title":"A sensitive fibre optic pH sensor using multiple sol-gel coatings","volume":"3","author":"Lee","year":"2001","journal-title":"J. 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