Amino Acid Fingerprints
Publication No. 12628
Detectives use ninhydrin to reveal fingerprints left at crime scenes. Ninhydrin reacts with amino acids found in the natural oils on our skin to produce a purple product. The intensity of the color may also be used as quantitative test for the amount of amino acids.
Ninhydrin solution in butyl alcohol, 0.5%, 5 mL*
Blotting paper, 9" wide x 4" long*
Hot plate or high temperature hair dryer
*Materials included in kit.
Work in a fume hood or well-ventilated area. Ninhydrin is a skin and eye irritant and is dissolved in butyl alcohol, a flammable solvent. Keep away from flames or other sources of ignition. Ninhydrin will stain skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Blotting paper may be disposed of in the trash following Flinn Suggested Disposal Method #26a. The ninhydrin solution may be stored for future use.
Cut each sheet of blotting paper (9" x 12") into thirds lengthwise to obtain three 9" x 4" pieces. Each piece of paper can be used to make two sets of prints, one set with ninhydrin, another set with ink to serve as a reference.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesConstructing explanations and designing solutions
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
HS-LS1.A: Structure and Function
HS-LS1.C: Organization for Matter and Energy Flow in Organisms
Crosscutting ConceptsStructure and function
Energy and matter
MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Ninhydrin is a pale yellow solid. It reacts with amino groups in amino acids and proteins to produce a purple product (Equation 1). The reaction is very slow in the absence of heat—heat is therefore used to speed up the “fingerprinting” reaction. All amino acids will test positive with ninhydrin.
Latent fingerprints are composed of several chemicals that are naturally present in skin oils or released through the pores of the skin via perspiration. Some of the chemicals in fingerprints include sodium chloride, amino acids, glucose, lactic acid and ammonia.
This activity was adapted from Biochemistry—The Molecules of Life, Flinn ChemTopic™ Labs, Volume 20; Cesa, I., Editor; Flinn Scientific: Batavia, IL (2002).