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 (Osub2/sub) and carbon dioxide (COsub2/sub) 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 COsub2/subsensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The Osub2/sub- and COsub2/sub-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 Osub2/suband COsub2/subsensors have sensitivities of IsubNsub2/sub/sub/Isub100%Osub2/sub/sub=22.8 and IsubNsub2/sub/sub/Isub100%COsub2/sub/sub=3.6, respectively. The response times of the optical Osub2/subsensor were 15 s upon switching from nitrogen to Osub2/suband 41 s when moving from Osub2/subto nitrogen (Nsub2/sub). The response times of the optical COsub2/subsensor were 7 s upon switching from 100% Nsub2/subto 100% COsub2/suband 39 s when moving from 100% COsub2/subto 100% Nsub2/sub. The proposed optical dual sensor can be used for the simultaneous sensing of Osub2/suband COsub2/subconcentrations in environmental applications.