Optical sensor for dual sensing of oxygen and carbon dioxide based on sensing films coated on filter paper

An optical sensor for the dual sensing of oxygen (O₂) and carbon dioxide (CO₂) based on sensing films coated on filter paper is proposed. Ethyl cellulose (EC) doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and 7-amino-4-trifluoromethyl coumarin serve as the oxygen sensing material and reference blue emission dye for the pH indicator, respectively. The CO₂ sensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The O₂- and CO₂-sensitive materials can both be excited with a 405 nm LED, and the two emission wavelengths can be detected separately. The experimental result reveals that the optical O₂ and CO₂ sensors have sensitivities of I_N/I_100%O=22.8 and I_N/I_100%CO=3.6, respectively. The response times of the optical O₂ sensor were 15 s upon switching from nitrogen to O₂ and 41 s when moving from O₂ to nitrogen (N₂). The response times of the optical CO₂ sensor were 7 s upon switching from 100% N₂ to 100% CO₂ and 39 s when moving from 100% CO₂ to 100% N₂. The proposed optical dual sensor can be used for the simultaneous sensing of O₂ and CO₂ concentrations in environmental applications.