It’s a question I’m asked probably once a week. “What wavelength do I select on my luminometer when performing a luciferase assay?” The question is a good and not altogether unexpected one, especially for those new to bioluminescent assays. The answer is that in most cases, you don’t and in fact shouldn’t select a wavelength (the exception to this rule is if you’re measuring light emitted in two simultaneous luciferase reactions). To understand why requires a bit of an explanation of absorbance, fluorescence, and luminescence assays, and the differences among them.
Absorbance, fluorescence, and luminescence assays are all means to quantify something of interest, be that a genetic reporter, cell viability, cytotoxicity, apoptosis, or other markers. In principle, they are all similar. For example, a genetic reporter assay is an indicator of gene expression. The promoter of a gene of interest can be cloned upstream of a reporter such as β-galactosidase, GFP, or firefly luciferase. The amount of each of these reporters that is transcribed into mRNA and translated into protein by the cell is indicative of the endogenous expression of the gene of interest.
In May 2017, a surprising discovery was made in the woods of Bayfield County, Wisconsin, just about a 5-hour drive north of Promega headquarters. Jonathan Martin, Associate Professor of Forestry at Northland College, was exploring the forest with an ultraviolet (UV) light in search of fluorescent lichen or plant life. What he found instead was a bright pink glow coming from a most unexpected source—a flying squirrel.
Have you ever walked on a beach and noticed that the waves seem to glow as they roll onto shore? Perhaps you have seen fish or jellyfish that glow in the dark, or maybe you’ve chased fireflies in your backyard or on a camping trip. These are all forms of luminescence (the production of light without adding heat), but the manner that these organisms produce their light can be quite different.
The music is loud, the bass is thumping, people are dancing and laughing, and my gin and tonic is glowing. This Friday night is perfect. This mysterious glowing drink catches the eye of many passersby and is a great conversation starter. At least it was until I learned why my drink was glowing. These days, when someone mentions my glowing drink, I am compelled to explain why. It has become a great conversation ender!
I’m a scientist and naturally curious, but there are some things I choose to not investigate just to hold on to the excitement that comes with wondering why something is the way it is. My desire to keep wondering why my gin and tonic glows, or becomes fluorescent, in the club was thwarted one Friday afternoon (ca. 2001) by Professor David Jameson, University of Hawai’i, in a Biophotonics lecture at the University of Wisconsin – Madison. Professor Jameson, who studied under the late, great Gregorio Weber, is a dynamic teacher with a genuine passion for fluorescence methodology. Continue reading “When You Got the Glow: The Truth About Your Gin and Tonic.”
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