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The home of the bright green river is Chicago, Illinois. They’ve been dyeing the river for St. Patrick’s Day since 1961.1 Originally, they used Fluorescein, but this showed detrimental effects in aquatic organisms. Fluorescein sodium is still used for staining human eyes to check for damage and is a highly valuable fluorescent dye besides!2
Instead of putting it in the office water cooler, we examined the excitation, absorption, and emission spectra for Fluorescein in deionised water using the FS5 Spectrofluorometer. The FS5 is equipped with a continuous Xenon lamp as an excitation source, and a PMT-980 photon counting detector. Additionally, the reference detector can be used to measure transmission. This allows the measurement of absorption against a solvent blank.
Figure 1. Excitation (black), absorption (green), and emission (red) spectra for Fluorescein in deionised water. (λem = 524 nm, range 300-520 nm, step 1, dwell 0.5 s, BWex 1.7 nm, BWem 1.1 nm. λex 462 nm, range
465-800 nm, step 1, dwell 0.3 s, BWex 1.7, BWem 1.1. Transmission 300-600 nm, step 1 nm, dwell 0.3 s, BWex 2 nm.)
