Highly sensitive and linear optical fiber carbon dioxide sensor based on sol–gel matrix doped with silica particles and HPTS

This paper presents a high-sensitive and linear fiber-optic carbon dioxide (CO2) sensor based on a sol–gel matrix composed of n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) doped with 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt (HPTS, PTS-), silica particles and a tetraoctylammonium hydroxide (TOAOH) phase transfer agent (i.e. the base). The experimental results indicate that the relative fluorescence intensity of the ion pair form of HPTS dye decreases as the CO2 gas phase concentration increases. The sensor has a sensitivity of approximately 26 and exhibits a uniquely linear response for CO2 concentrations in the range of 0–100%. The sensitivity of the optical fiber CO2 sensor is quantified in terms of the ratio IN2/ICO2,IN2/ICO2, where IN2IN2 and ICO2ICO2 represent the detected fluorescence intensities in pure nitrogen and pure carbon dioxide environments, respectively. The response time of the sensor is 9.8 s when switching from a pure N2 atmosphere to a pure CO2 atmosphere and 195.4 s when switching from CO2 to N2. The signal changes are fully reversible as the atmosphere is switched repeatedly between N2 and CO2. Overall, the experimental results demonstrate that the use of a sol–gel matrix doped with the ion pair form of HPTS and silica particles uniquely enhances the sensitivity and linearity of the proposed optic-fiber CO2 sensor.