Forensic

If you ever watch CSI you'll noticed that for making a fingerprint visible they do something called fumigation. For this they need a chemical compound called cyanoacrylate. It's a usual chemical compound we found in our daily life, since it's the major compound of Super Glue. In CSI, they heating this chemical compound and then the fumes come out and make the fingerprint visible. Then, how this trick works?

Methyl 2-cyanoacrylate, taken from wikipedia.org

First thing, before talking any further, is we must know what cyanoacrylate is. Cyanoacrylate is a generic name for group of chemical compound used usually as adhesive. The one in the left is a methyl 2-cyanoacrylate. It has a liquid state in normal condition. When it makes a contact with moisture or hydroxide ions (e.g. from water) it turns into solid state. If this happen when it applied into two surfaces, they will bound together and is hard to separated. That's why cyanoacrylate is one of the best adhesive in the world. It can be applied as soon as possible and the result is perfect.

So how these properties help the forensic? Fingerprints are either visible or not. If it's visible, the forensics can take the picture as soon as possible to run it in their database. But if it's invisible that means there's something to do to make it visible. Since fingerprint came from a skin, it transfers sweat and any other organic molecules from finger. When the sweat vaporized, the solid constituents like fatty acid and proteins are left behind. Cyanoacrylate works by interact with the hydroxide ions of these molecules, and the result is a solid structure of the cyanoacrylate that follows the shape of the fingerprint. That means, the invisible one become invisible enough to record.

Cyanoacrylate fumes can make irritation in eyes, nose, or throat. But it's not toxic. You can try to see your own fingerprint at home, too. Just prepare an electrical heater, some drops of Super Glue, a chamber (glass or other stuffs that can hold the fumes), and a sample of your fingerprint. You can use mirror as example. Put the mirror inside the chamber and start to fumes the Super Glue by heating it. After a while, you'll start to see your fingerprint! Caution: Do it in a ventilated room and never inhale it. Good luck!