Optical CO2 sensor with the combination of colorimetric change of α-naphtholphthalein and internal reference fluorescent porphyrin dye

A new optical CO₂ sensor based on the overlay of the CO₂ induced absorbance change of pH indicator dye α-naphtholphthalein with the fluorescence of tetraphenylporphyrin (TPP) was developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO₂ concentration. The ratio I₁₀₀/I₀ values of the sensing films consisting of α-naphtholphthalein in ethyl cellulose layer and TPP in polystyrene layer, where I₀ and I₁₀₀ represent the detected luminescence intensities from a layer exposed to 100% nitrogen and 100% CO₂, respectively, that the sensitivity of the sensor, are more than 53.9. The response and recovery times of the sensing films consisting of α-naphtholphthalein in ethyl cellulose layer and TPP in polystyrene layer were less than 5 s for switching from nitrogen to CO₂, and for switching from CO₂ to nitrogen. The signal changes were fully reversible and no hysterisis was observed during the measurements. The highly sensitive optical CO₂ sensor based on fluorescence intensity changes of TPP due to the absorption change of α-naphtholphthalein with CO₂ was achieved.