An optical CO2 sensor based on the overlay of the CO2 induced absorbance change of pH indicator dye alpha-naphtholphthalein in poly(trimethylsiliypropyne) (poly(TMSP))layer with the fluorescence of tetraphenylporphyrin (TPP) in polystyrene layer is developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO2 concentration. The ratio I-100/I-0 value of the sensing film, where I-0 and I-100 represent the detected luminescence intensities from a layer exposed to 100% argon and 100% CO2, respectively, that the sensitivity of the sensor, is estimated to be 10.3. The response and recovery times of the sensing film are less than 3.0 s for switching from argon to CO2, and for switching from CO2 to argon. The signal changes are fully reversible and no hysteresis is observed during the measurements. The highly sensitive and fast responsible optical CO2 sensor based on fluorescence intensity changes of TPP due to the absorption change of alpha-naphtholphthalein with CO2 is achieved using poly(TMSP) film. (c) 2005 Elsevier B.V. All rights reserved.