Publications

@article{Liu2022-fh,

title = {A single-film fiber optical sensor for simultaneous measurement 

 of carbon dioxide and relative humidity},

author = {Liangliang Liu and Stephen P Morgan and Ricardo Correia and Serhiy Korposh},

year  = {2022},

date = {2022-03-01},

journal = {Opt. Laser Technol.},

volume = {147},

number = {107696},

pages = {None},

publisher = {Elsevier BV},

abstract = {Colorimetric measurement is a versatile, low-cost method for 

 bio-/chemical sensing and that has importance in biomedical 

 applications. General carbon dioxide (CO2) sensors based on 

 colorimetric change of a pH indicator report only one parameter 

 at a time and are cross-sensitive to relative humidity (RH). 

 This work describes a novel optical fiber sensor with a thin 

 film on the distal end of the fiber, combining colorimetric 

 measurement and a white light Fabry-P\'{e}rot interferometer 

 (FPI) for the simultaneous measurement of CO2 and RH. The CO2 

 sensitive dye ion-pair: thymol blue and tetramethylammonium 

 hydroxide are encapsulated inside organically modified silica 

 forming an extrinsic FPI cavity (refractive index of 1.501 $±$ 

 0.02 and thickness of 5.83 $±$ 0.09 μm). The sensor 

 reversibly responds to 0-6% CO2 and 0-90% RH with negligible 

 cross-sensitivity and allows measurement of both parameters 

 simultaneously. A sensitivity of ∼0.19 nm/%RH is obtained for 

 RH measurement based on the wavelength shift of the FPI and 

 there is a polynomial correlation between the average intensity 

 of selected wavelengths and the concentration of CO2. The 

 applicability of the sensor is demonstrated by measuring the CO2 

 and RH exhaled from human breath with a percent error of 3.1% 

 and 2.2% respectively compared to a commercial datalogger. A 

 simulation model is provided for the dye-encapsulated FPI sensor 

 allowing simulation of spectra of sensors with different film 

 thicknesses.},

keywords = {Colorimetric change, Fabry-P{\'{e}}rot interferometer, Multiparameter sensing, Optical fiber sensor, Relative humidity, Respiration},

pubstate = {published},

tppubtype = {article}

}