From psychedelic turtles to life-saving scorpions, we’ve certainly seen our fair share of fluorescence pop up in the natural world. But very few of us actually get to witness this phenomenon with our own two eyes. As it turns out, you probably have something in your pantry at this very moment that emits a brilliant green when hit with a laser – and you use it to make sandwiches. Yes, regular, run-of-the-mill peanut butter glows in the dark.
So what’s going on here, and why can you only see the glow for a split second? Peanuts contain a multitude of phenols – chemical compounds that often act as protective agents for the plant – which are known to absorb light in the ultra-violet spectrum.
When hit with energy, say, by our NurdRage host’s UV laser pointer, light is absorbed by the compounds and re-emitted as light-energy in the green spectrum. This “delayed luminescence” (also sometimes called “delayed fluorescence”) was discovered some 50 years ago, but we’re still working out just which compound causes it.
The “afterglow” is stronger in peanut butter than whole peanuts because of the way the nuts are processed. Crushing and heating the nuts causes some of the larger compounds to breakdown into their components, allowing them to react more freely. Freezing enhances the effect for the same reason it stops fruit from ripening: it slows (but doesn’t halt) chemical reactions within the plant.
You might not have any liquid nitrogen lying around, but you could try this with dry ice. So go, be merry, and make glowing PB&Js … just remember that lasers can blind you, and ice burns hurt. Always be careful when sciencing at home!