| Summary: | Simultaneous detection of carbon dioxide (CO<sub>2</sub>) and oxygen (O<sub>2</sub>) has attracted considerable interest since CO<sub>2</sub> and O<sub>2</sub> play key roles in various industrial and domestic applications. In this study, a new approach based on a fluorescence ratiometric referencing method was reported to develop an optical dual sensor where platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) complex used as the O<sub>2</sub>-sensitive dye, CdSe/ZnS quantum dots (QDs) combined with phenol red used as the CO<sub>2</sub>-sensitive dye, and CdSe/ZnS QDs used as the reference dye for the simultaneous detection of O<sub>2</sub> and CO<sub>2</sub>. All the dyes were immobilized in a gas-permeable matrix poly (isobutyl methacrylate) (PolyIBM) and subjected to excitation using a 380 nm LED. The as-obtained distinct fluorescence spectral intensities were alternately exposed to analyte gases to observe changes in the fluorescence intensity. In the presence of O<sub>2</sub>, the fluorescence intensity of the Pt (II) complex was considerably quenched, while in the presence of CO<sub>2</sub>, the fluorescence intensity of QDs was increased. The corresponding ratiometric sensitivities of the optical dual sensor for O<sub>2</sub> and CO<sub>2</sub> were approximately 13 and 144, respectively. In addition, the response and recovery for O<sub>2</sub> and CO<sub>2</sub> were calculated to be 10 s/35 s and 20 s/60 s, respectively. Thus, a ratiometric optical dual gas sensor for the simultaneous detection of O<sub>2</sub> and CO<sub>2</sub> was successfully developed. Effects of spurious fluctuations in the intensity of external and excitation sources were suppressed by the ratiometric sensing approach.
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