An emission based optical CO₂ sensor fabricated on grating-like TiO₂ substrates using HPTS

TiO₂ is a widely used material in various applications, including photo-catalysis, sensing, and dye-sensitized solar cells. In this work, we presented a stable and sensitive CO₂ sensor working on principle of emission signals of the HPTS dye immobilized on TiO₂ substrates whose effectiverefractive indicesin the parallel and perpendicular grating orientations evidenced earlier. The HPTS exhibited 8.4-fold enhanced emission signal on the offered substrates with respect to the previously reported intensities recorded for the polymeric supports. The emission peaks of the HPTS exhibited CO₂ induced intensity quenching when excited at 466 nm. Calibration sensitivity of the offered composites has been tested exposing the sensor materials to varying concentrations of the CO₂ between 0.0 and 100.0 % pCO₂ and correlating the measured fluorescence intensity with the corresponding CO₂ levels. The dye revealed enhanced CO₂ induced response exhibiting the I₀/₁₀₀ values of 11.9, 13.3, 11.2 and 6.5. We also recorded bi-exponential excited state lifetimes for the HPTS on four different test materials both in the absence and presence of the CO₂. The emission based variations were followed as the analytical signal due to higher CO₂-induced relative signal changes than that of the lifetime based variations. Herein we used the ion pair form of the HPTS in a protective chemical microenvironment and obtained considerable long term stability extending to16 mounts which can be attributed to the presence of the 1-butyl-3-methylimidazolium tetrafluoroborate as an internal buffering system in the sensing composition as well as the inert and robust structure of the substrate. The extremely high optical response, advantage of excitation with blue LEDs and long-term stability observed on grating-like TiO₂ surfaces make the proposed system a promising design for the quantification of CO₂ for further applications.