A simple single-detector system for simultaneous monitoring of O 2 and CO 2 gas concentration

Abstract

In this paper, we present a system for fluorescent monitoring of multiple gas concentrations using a simple and robust single detector setup. Two gas-sensitive fluorescent films are illuminated by two separate excitation sources modulated at different frequencies. Cross-polarization is used to shield the excitation light from the detector, allowing fluorescent signals from both films to be simultaneously monitored and quantified using a microprocessor and lock-in detection. Simultaneous detection of O₂ and CO₂ in a mixture of gases is done as a proof-of-concept of this frequency discrimination technique. The detection of oxygen is based on the fluorescence quenching of platinum octaethylporphine (PtOEP) lumiphore in presence of O₂. The detection of CO₂ is based on fluorescence quenching of hydroxypyrene trisulfonic acid trisodium salt (HPTS) in presence of CO₂. A single microprocessor is used to drive the excitation source (different color LEDs), and sample and analyze the detector response at the two different frequencies. The device demonstrated minimal crosstalk between the O₂ and CO₂ signals. The O₂ concentration was measured in the useful range between 20 and 0%, and CO₂ demonstrated a useful range between 5% and 0%. The polarization filtering is color-independent and can be readily extended to systems with more than two colors; due to the frequency discrimination, it is immune to cross-talk in which one dye excites another. The whole arrangement is a compact, lowcost, simultaneous multi-color fluorescent sensor system suitable for many biological, chemical, and gas-monitoring applications.