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A reflection-mode fibre-optic sensor for breath carbon dioxide measurement in healthcare

Liu, LiangLiang; Hao, FengHuan; Morgan, Stephen P.; Correia, Ricardo; Norris, Andrew; Korposh, Serhiy


LiangLiang Liu

FengHuan Hao

Andrew Norris

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Professor of Photonics Instrumentation


A reflection-mode carbon dioxide (CO2) fibre optic sensor (FOS) is developed based on the colorimetric change of pH indicator dye thymol blue. The CO2 sensing film comprises thymol blue and tetramethylammonium hydroxide in the form of an ion pair doped in an organically modified silica film. A dip coating process was conducted to coat the sensing film on the tip of optical fibre with a film thickness approximately 2.7 ± 0.1 μm. The observed reflection signal at a wavelength of 608 nm exhibits a reversible change for the concentration of CO2 range from 0 to 6% with a response time of 19 s and recovery time of 170 s for 6% of CO2. An optimal concentration of thymol blue in the preparation of coating solution that provides a highest sensitivity was found to be 2.9 mg/ml. Storing the FOS in a pure nitrogen atmosphere provided a stable film with a shelf-life of over 15 days as compared to a gradual degradation in film performance and complete loss of sensitivity after 10 days with storage in ambient air. The FOS response is affected by relative humidity (RH) and a humidity filter was demonstrated to reduce humidity levels in breath from 90% to 40–50% to reduce this effect. The developed FOS was used to measure the end-tidal breath CO2 for testing its applicability in healthcare. The CO2 measurement from breath sample using our FOS shows a good agreement (percentage error~3%) with a commercial CO2 datalogger (K-33 BLG, CO2 Meter, USA). Due to the limitation of response time, at present the FOS is limited to measuring variation of the CO2 from slow breath to breath.


Liu, L., Hao, F., Morgan, S. P., Correia, R., Norris, A., & Korposh, S. (2019). A reflection-mode fibre-optic sensor for breath carbon dioxide measurement in healthcare. Sensing and Bio-Sensing Research, 22, Article 100254.

Journal Article Type Article
Acceptance Date Dec 18, 2018
Online Publication Date Dec 19, 2018
Publication Date 2019-02
Deposit Date Jan 17, 2019
Publicly Available Date Jan 17, 2019
Journal Sensing and Bio-Sensing Research
Electronic ISSN 2214-1804
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 22
Article Number 100254
Keywords Optical fibre CO sensor, Colorimetric change, pH indicator, Thymol blue, Sol-gel, End-tidal CO
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Additional Information This article is maintained by: Elsevier; Article Title: A reflection-mode fibre-optic sensor for breath carbon dioxide measurement in healthcare; Journal Title: Sensing and Bio-Sensing Research; CrossRef DOI link to publisher maintained version:; Content Type: article; Copyright: © 2019 The Authors. Published by Elsevier B.V.


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