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Playing Detective: Dusting for Fingerprints and Looking at Them Under the Microscope

As with the world of microorganisms, there are many things that cannot be seen with the naked eye and you need to use instruments such as the microscope to view them. Fingerprints can be used to identify the criminal who had handled the knife used to kill a person at the crime scene, for example, but we cannot see these fingerprints on our own. We see how detectives on TV lift fingerprints off from things like door knobs and matching them with the right person’s fingerprint. Kids and children could do this as well, and they won’t even have to leave home to do it. This simple microscope activity would be an interesting way to test your detective skills as well as your microscope knowledge. First, we have to dust the fingerprints, then we transfer the print on to something like tape (the transparent kind). Only then could we view the fingerprint under the microscope lens.

For this forensic science microscope activity you’re going to need some cocoa powder, tape (transparent), blank microscope slide, a pair of tweezers and a fine paintbrush. Let us begin by choosing what part of the house you want to lift a fingerprint from. This would work best if you’re going to choose an object with a smooth surface like mirrors and door knobs. For example you’re going to be looking at fingerprints lifted from the door knob, this is what you’re going to do:

First, sprinkle some of the cocoa on the surface of the knob. The oil from your hands would have left some marks on the door knob and the cocoa would stick to the oil and form around the prints of your hand—and more importantly, your fingers. Blow off the rest of the cocoa and check if you’ve got yourself a fingerprint. Cut off a piece of tape and press the sticky side onto the fingerprint. Rub your finger on the tape several times to make sure that the whole fingerprint would be ‘lifted off’ onto the tape. Take the tape off from the knob with a pair of tweezers (you don’t want your own fingerprints in there too!) and place it on a blank microscope slide. Now that you have mounted your fingerprint on a slide, it’s time to examine it under the stereo microscope. Place the slide on the microscope stage and clip it in place. You could look at this slide with either the incident or transmitted light. The incident light comes from the lamp on the top of the microscope stage while the transmitted light is the lamp under the stage. The latter passes light through the object and would be quite good to provide some contrast on the image so that you could see the object through the microscope lens better. Since we’ve used cocoa in this case, which is a dark colored powder, it would be quite easy to distinguish the fingerprint you have lifted.

Examine the fingerprint carefully under your stereo microscope and try to match it with its owner. You could take fingerprint samples from the rest of your family by asking them to press their fingertips onto a stamp pad and placing their fingertips on a blank sheet of paper. Compare their fingerprints with the one you have on your slide. Now you can even know who among your family opened the door first thing in the morning!

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