Day 3: Forensic Chemistry

The Case: Mittens has been Catnapped!

A famous cat (who poses for TV commercials, calendars, etc.) has been catnapped from its owners house. This is mittens.

This is the crime scene.

To find out who catnapped Mittens, you lifted the fingerprints from each of the three pens (3) on the table, determined which pen wrote the ransom note (2) using thin-layer chromatography (TLC), analyzed the fingerprint that was found on the note when a black (UV) light was shown on it, determined which spot(s) on the napkin (4) was blood using luminol, and then used gel electrophoresis to analyze the DNA from that blood.

Activity 1: Making Fingerprints

You first made fingerprints on a card and analyzed your own fingerprints to determine what general shape they had (arches, loops, whorls, etc.). You can find these shapes at http://www.fbi.gov/kids/k5th/whatwedoe3.htm.

Activity 2: Enlarging a Fingerprint with a Balloon

You can "magnify" a fingerprint by simply placing the print on a balloon and then inflating. It works best when you use a Sharpie maker.

Activity 3: Developing and Lifting a Print with Fluorescent Fingerprint Powder

To visualize a fingerprint on a surface, it is usually dusted with fingerprinting powder. Once the fingerprint is dusted, it can be lifted using tape. You used fluorescent yellow fingerprint powder to dust a print, lifted it with a piece of tape and then placed the fingerprint on a piece of black construction paper. The fingerprint glows brighter when a blue light (with an orange filter) is used. Watch the video below.

Activity 4: Developing a Fingerprint By Fuming with Superglue

Sometimes on TV you will see CSI people develop a fingerprint using superglue fumes. This actually works as the fumes from the glue adheres to the oils left from a finger. Watch the video below and see the final result as well.

Activity 5: Using Magnetic Fingerprinting Powder to Lift Prints from Pens (Who Wrote the Ransom Note?)

To figure out who catnapped Mittens, you needed to lift the fingerprints from the pens found at the crime scene. Magnetic fingerprinting powder works well on smooth surfaces and you used this to lift the prints fro the pens. Watch the video below and see the results.

Activity 6: Whose Fingerprint is on the Ransom Note

The catnapper left a fingerprint on the ransom note that can be seen under a black (UV) light. A picture of the note and fingerprint are below.

Activity 7: Using Thin-Layer Chromatography (TLC) to Determine Which Pen Was Used to Write the Ransom Note.

The ransom note (below, left) was written with one the pens found at the crime scene. To determine which pen was used, the ink from the note was obtained by punching out a portion of the note (the ball of yarn) and placing the paper and ink in a solvent. Samples of the inks were then obtained from each pen and also dissolved in a solvent. Spots of each ink was spotted onto a TLC plate (below, center) and the plate was placed into a jar of the solvent and allowed to develop. The pen inks will separate and the ink from the ransom note is then compared to each pen ink (below, right). Do you remember which pen was used to write the ransom note? Watch the video below.

Activity 8: Which Spot on the Napkin is Blood?

A napkin found at the crime scene had two spots on it (below). Is one of the two spots blood? Whose blood is it? To determine if a spot was blood, we used chemiluminescence (like you saw in Day 2). Luminol was reacted with hydrogen peroxide and the iron in blood to provide light. The second picture below has had luminol and hydrogen peroxide added. Which spot is blood?

Activity 9: DNA Gel Electrophoresis of DNA Obtained from the Blood.

The DNA from the blood stain and samples from each of the suspects were analyzed using gel electrophoresis (actually, we used acid/base indicators in the electrophoresis apparatus, not real DNA). Watch the video below of how the samples were loaded and see the final results below. Whose DNA was on the napkin?

Starting DNA Gel:

Final DNA Gel:

Activity 10: Extracting DNA from Strawberries

The final activity of the day was to extract DNA from strawberries. You had to mash up the strawberries, use a "lysis" solution that would break open the cells (where the DNA is found), filter the solution to remove the solids and then by adding cold ethanol to the solution, the DNA would precipitate between the two layers. You placed it into a bottle and took it home. Pictures from the process are below.