Demonstrate one of the simplest and most common methods of developing “latent” fingerprints—invisible fingerprints left behind on porous surfaces such as paper and cloth. Latent fingerprints are composed of several chemicals that are naturally present in skin oils or released through the pores of the skin by perspiration. Ninhydrin, a colorless organic compound, reacts with amino acids found in skin oils to form a bright purple product. The resulting purple “amino acid fingerprints” can then be photographed and processed. In this demonstration, student volunteers make invisible fingerprints on a special blotting paper. The fingerprints are then developed by spraying the paper with ninhydrin solution and heating the product. Use the water soluble ink pad provided with the kit to make a second set of fingerprints for identification purposes. A great activity to show the science behind forensic investigations!
Concepts: Amino acids, ninhydrin reaction, fingerprinting.
Time Required: 30 minutes
Materials Provided: Blotting paper, ink pad, ninhydrin solution, spray bottle.
Note: Enough blotting paper and ninhydrin solution are provided to make 30 sets of “amino acid fingerprints.”