This one is a much larger molecule than we usually do, but it’s easy to forget that enzymes (and all proteins) are really just very large molecules. Taq polymerase is a DNA polymerase (DNA-copying enzyme) from the microorganism thermus aquaticus, a bacterium that lives in very hot water. Read the rest of this entry »

Monday, I remarked that cyanoacrylate (superglue) adhesives are used by some forensic scientists to expose fingerprints on objects. I actually hadn’t heard of the procedure before and was eager to try it out. As anyone who has known the pleasure of my company for very long can attest, I am not the most patient person in the world. It is with great pleasure that I bring you yet another MOTD experiment, with more camera phone quality pictures!

The general idea here is that cyanoacrylate adhesives are volatile. The most likely cyanoacrylates you’ll encounter are the methyl and ethyl esters, the boiling points of which people seem to disagree on a bit. I decided to just try using a bath of hot water from my faucet, which is about 60C, or 140F, and hoped that would vaporize enough adhesive. Superglue stinks quite a bit, so you know it’s got at least an OK vapor pressure.

I then had to find a) a developing chamber and b) some stuff to get fingerprints on. I’d read that light surfaces were bad for this, since white-on-white was hard to see, so I got whatever I could find that was opaque and in a variety of colors.

The developing chamber ended up being an old pipet tip box (I had intended to use one of those disposable tupperware/gladware containers, but they were occupied by a few, ahem, ongoing experiments with sourdough starters). For fingerprinty objects, I briefly manhandled a Gatorade cap, a Listerine Freshstrips box, and my old Blockbuster Rewards card. My usual clumsiness, compounded by cheap Chinese-manufactured superglue tubes, had resulted in an unfortunate accident which temporarily rendered my right hand incapable of leaving fingerprints, so I had to use old lefty. In the box these went, with about half a mL of superglue squirted into each of two corners. The whole mess went into my science breadpan, filled with an inch or so of hot water. I left it to float for half an hour or so. The image is right before I took it out:

After taking it out, in a rare case of before-the-fact common sense, I put the whole thing in the fridge for about 10 minutes to cool down. This way, I wouldn’t be greeted by a cloud of noxious cyanoacrylate fumes, aching to polymerize on my eyes and sinuses. Below, you can see that it worked, sort of. The fingerprints are actually quite clear in person. Mostly on the Blockbuster card, but you can see a bit on all three. It is probably for the best that I don’t have high-resolution shots of my fingerprints online.

If you haven’t handled much superglue, you might be inclined to think the exposed fingerprints are a powdery, flaky coating based on appearances. It’s not. They are just as hard as any other cured superglue. The exposure is actually a negative cast of my fingerprints, in polycyanoacrylate! This works because your fingerprints contain enough bases (water, certain basic parts of proteins, maybe even certain fats) to initiate superglue polymerization. Let me know if you try it! See you tomorrow.