A common way to lift fingerprints is to dust
a powder over the suspect area of a material,
let the powder stick to the oil, sweat left by
the finger, and then lift the fingerprint with
tape. When using this method, the important
things to keep in mind are:
1. How well does the powder stick to the
oils/sweat in the fingerprint?
2. How well does the powder stick to the
surface which you are dusting for prints?
Ideally, what you want is a powder that sticks
strongly to the print, but does not stick at all
to the surface. You can imagine that you
wouldn't be able to lift a very good fingerprint
if the powder also stuck to the surface in
addition to the print! This means that you have
to take advantage of the different properties of
a fingerprint versus the surface which it is on.
Fingerprints are made of mostly oil and sweat,
so if your surface is something like glass,
plastic, or maybe a metal door handle, you would
want a powder that likes to stick to oil/sweat
but not any of these other materials. You can
experiment with several household powders like:
1. Pencil lead
2. Talcum powder
3. Corn starch
Pencil lead is a particularly interesting
system. Pencil lead is made of graphite which is
made up of carbon atoms. What you can do is get
some mechanical pencil lead and crush it to a
powder. Then, dust the powder over a surface
(such as a glass) where you left a print. The
pencil lead should stick to the fingerprint and
not to the glass. Once you can see the print,
you can take some clear tape and apply the
sticky side to the fingerprint. When you pull
the tape off, the fingerprint should now be
stuck to the tape. You can then stick that tape
on a piece of paper, and write a note of when
and where it was collected (remember, you always
have to label your evidence!). Now what you can
do, is experiment with how much you crush the
pencil lead and how well of a print you can lift
(if you crush it to a really fine powder is it
better than if the lead is still pretty
granular? Why?). You can also do the same thing
with the other powders. Another thing you can
test is: does the age of the print affect your
ability to lift a fingerprint with this method?
In other words, if you press your finger to a
glass, can you lift a print and hour later? Can
you lift a print a day later? Can you lift a
print a week later? If there is a difference,
can you explain why?
In CSI like crime labs, forensic experts use
many different techniques to lift prints. Some
of them involve depositing a vapor on the
surface which then reacts with chemicals in the
fingerprint. Another method involves reacting
ninhydrin with the amine groups in proteins in
the fingerprint. When ninhydrin reacts with
amine, it changes color (usually a purple color)
which would then show where the fingerprint is.
I work as a graduate student. This means that I
split my time between going to class and doing
research in a laboratory. In the lab, I use
different chemical reactions to build new
molecules and materials such as polymers.
Polymers are very useful. Polymers are
everywhere: plastic bottles, rubber bands,
organic solar cells (polymers that convert light
energy into electrical energy), and even DNA and
proteins are all polymers. I enjoy my work, and
I hope to design new polymers that can be useful
and make the world a better place.
Good luck with your experiments!
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