Happy Halloween!
Halloween is fast approaching 👻 so why don’t you try out this fun experiment with your kids?
The next time you’re out in the woods, collect a few fresh twigs from a Horse Chesnut tree and carry them home. Identifying the right tree is easy at this time of year with all the fruit lying on the ground. With secateurs, make a fresh cut from a small branch then suspend the freshly cut end in a large glass or beaker of water. Turn off the room lights and shine a small UV lamp or blacklight onto the beaker. Here’s a short video of what happens…
So what on Earth is going on here?
This strange fluorescent emanation is not some “Ghostbuster’s ectoplasm” but in fact comes from a chemical called aesculin which is present in the sap of the Horse Chestnut tree. It is also present in the roots of the dandelion plant and in olive tree bark.
Aesculin belongs to the family of coumarin glucosides with the chemical structure shown here.
You should wash your hands after the demonstration because the presence of aesculin makes Horse Chestnut fruit toxic. So if you go out collecting Sweet Chestnuts for roasting and eating at this time of year, which are edible, you have to be careful to avoid Horse Chestnuts, which come from a totally different tree and genus. More information can be found online.
Aesculin fluoresces strongly under UV light with an eerie electric blue glow as shown in the above video.
The UV light you use should emit in the region 365 nm to 395 nm in the near UV. The low cost “black lights” that are used to detect pet urine stains around the home work extremely well. In addition, they are widely available and inexpensive. The lamp version with LEDs that emit at 365 nm works best, but lamps emitting at 395-400 nm are also quite effective.
Then watch the spooky effects as the tree sap containing aesculin slowly seeps out from the branch you have just cut and diffuses in the water.
And here below is the fluorescence spectrum of aesculin that was sampled directly from the beaker in the earlier video.
Happy Halloween 🎃👻🦇
Steve
Oh wow this is so cool! I wish they made science this interesting at school!