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Fluorescein—painting rivers green!

One common modification attached to oligos is the bright green fluorophore known as Fluorescein, FITC, or FAM (Fluorescein amidite). Attaching the fluorophore to oligonucleotides is not its only use though. Read on.

The Chicago River on St. Patrick’s Day 2009. While the tradition continues, fluorescein is no longer used to provide the green color; the current recipe is a tightly guarded secret (photograph courtesy of Mike Boehmer).
 In 1961 Steve Bailey was the business manager of the Chicago Journeymen Plumbers Union, Local 110. One afternoon a plumber stopped into the office wearing white coveralls that were nearly covered with green stains. When Bailey asked about the cause of the green stains, the plumber explained that he had been checking for potential sources of pollution to the Chicago River. This was done by dumping the bright green dye fluorescein into waste pipes around the river and checking to see if any of the green dye showed up in the river.

The bright green on the plumber’s coveralls gave Bailey an idea. Instead of using fluorescein as a pollution control, why not dump a hundred pounds of the stuff into the river, and turn the river green for St. Patrick’s Day? In an impressive display of the clout of a strong union in a strong union town, and that is just what they did.

So next St. Patrick’s Day pull out a FAM-labeled oligo from the back of your lab fridge, and raise a glass to the astoundingly useful dye, and then raise it one more time for that mighty bright green river, the Chicago.

IDT provides a selection of fluorescein dyes, including Fluorescein Freedom™ Dyes that have no patent licensing restrictions.

Published Jun 17, 2011
Revised/updated Jul 7, 2022