Simultaneous Single Detector Measurement of Multiple Fluorescent Sources

In many applications it is desirable to simultaneously measure the concentration of multiple fluorescent sources. In this paper, a simple robust technique for accomplishing this is realized by illuminating the fluorescent elements by excitation light modulated at different frequencies. A single microprocessor is used to drive the excitation sources (different color LEDs), and analyze the detector response at the two different frequencies. The excitation light at both colors is filtered by a single set of cross-polarized filters, and the signal from the single detector is locked-in to the different excitation light frequencies to simultaneously measure the response of different dyes. As proof-of-concept, this approach is demonstrated on two distinct systems. First, mixtures of concentrations of the fluorescent dyes trisodium 8-methoxypyrene-1, 3,6-trisulfonate and Rhodamine 6G in water are simultaneously measured in a standard fluorescence measurement. Then, the system is used for simultaneous detection of O₂ and CO₂ in a mixture of gases using two different gas-sensitive fluorescent films. The detection of oxygen is based on the fluorescence quenching of platinum octaethylporphine lumiphore in the presence of O₂. The detection of CO₂ is based on fluorescence quenching of hydroxypyrene trisulfonic acid trisodium salt in presence of CO₂. The whole arrangement is a compact and low-cost simultaneous multicolor fluorescent sensor system that is suitable for many biological, chemical, and gas-monitoring applications.