Fingerprint Detection

Objective

To detect and obtain the patterns of your fingerprint from any of your fingers.

Application

Forensics, Crime investigation, etc.

Difficulty

Procedure: Easy

Concept: Medium

This experiment contains toxic fumes, please be careful and check out our safety guide.

Concept

Fingerprint is the unique identity associated with different people. It is the pattern, or impression of the friction ridges, or the raised portion of the epidermis on the palm skin of all part of the finger. Such print may be deposited in natural hand secretions, or palmar sweat, and found on the palm sides of fingers. Identification of these fingerprints is an important system within police agencies, since lifting fingerprints from a crime scene can be used in forensic science to identify suspect or other people who touched a crime scene surface, or to recognize whether two fingerprints are from the same finger or palm.

Three types of prints, the plastic, visible finger print, and true latent prints are available at the crime scene. The plastics prints are ridge impressions on a soft material such as wax and the visible prints are ridge impressions on colored materials. Both types are directly visible to the eyes without any processing. Only the true latent prints, which is the transfer of body perspiration on finger ridge to the object surface, requires techniques to visualize the prints.

Latent Fingerprint
Plastic Fingerprint
Visible Fingerprint

Prints on non-absorbent surface by skin or dermal ridges can be developed with powder, while the prints on soft or porous surfaces require the visualization using chemical processing techniques.

One of chemical technique used for fingerprint visualization is Iodine fuming. When finger ridges come in contact with a surface receptive to a print, materials on the ridges, such as oil, will be transferred to the surface. The patterns on the paper might be different depends on the pliability of the skin, the pressure applied by the finger, and the degree of smoothness on the paper.

Therefore, when finger is pressed against a white paper, different patterns of the fingerprints are let on the paper. 1 At this time, iodine can be heated to produce a violet vapor that is then absorbed by the fingerprint secretion to produce a yellowish brown pattern on the surface where the secretions are deposited. Such visualization is short lived and needs to be chemically fixed by mixing with starch.

Materials

Procedure

Fixing the finger print

Analysis

Based on whether you press really hard onto the paper and the fingerprints fixed onto the paper, qualitatively, or determine the approximate force you need to apply to the paper in order to obtain a clear fingerprint of your thumb.

Conclusion

Does the fingerprint successfully appear onto the paper after placed into the tube and after fixed by the starch solution? Does more force required to obtain a clearer figureprints onto the paper? Were your fingerprints looking exactly the same when the fingerprints were obtained by compressing the paper using the same finger for multiple times?

Extension

Other parameters in the experiments can be examined as well. For example, tubes with different volume can be applied in different trials to see if the smaller volume of the tube can condense the iodine vapor inside the tube and give out clearer pattern of finger prints after the experiments. Similar, the different amount of iodine can also be tried in different trials, as well as the different location you placed the fingerprint inside the tube.

Not only does iodine can be applied in visualizing fingerprints, the similar protocol can be applied to cyanoacrylate fuming that forms white complex with the salt in figureprints. Similarly, silver nitrate, which reacts with the sodium chloride in the palmer sweat and forms complex, can be heated to fume and visualize fingerprint using similar protocol. Such complex needs to be visualize under UV-light, which is not accessible everywhere. Besides, silver is a heavy metal and much more expensive to purchase than iodine. Therefore, iodine is considered as a more accessible and realistic method to use.

Reference