#022: Ninhydrin Development of Fingerprints

Summary

In this engaging presentation, MP Dillahunty from UCA explores the use of ninhydrin in forensic science for developing fingerprints. He explains how ninhydrin reacts with amino acids in fingerprint residues, turning surfaces purple. The demonstration involves applying fingerprints to paper, immersing the paper in a ninhydrin solution, and then heating it to accelerate development. After a short wait, the vivid purple prints emerge, highlighting the effectiveness of this method in forensic investigations. Dillahunty emphasizes the importance of careful handling to avoid contamination, showcasing ninhydrin's long-standing role in law enforcement since 1954.

Takeaways

• 👤 MP Dillahunty introduces ninhydrin, a compound used in forensic science for developing fingerprints.
• 🔬 Ninhydrin reacts with amino acids secreted by the skin, which are present in sweat, causing a purple coloration.
• 📜 The technique of using ninhydrin to develop fingerprints on paper has been utilized by law enforcement since 1954.
• 🖐️ The presenter demonstrates how to create a print by placing fingers on paper, leaving behind fingerprint residue.
• 🧤 Cotton gloves are worn under other gloves to prevent contamination of evidence items with technician residue.
• 💧 Ninhydrin working solution is prepared by mixing solids with solvents for effective fingerprint development.
• 📈 The evidence paper is briefly immersed in the ninhydrin solution and then allowed to drip dry for development.
• ⏳ For optimal results, the evidence is usually left to develop for 24 to 48 hours, though heat can accelerate the process.
• 🔥 Using an oven, fingerprints can be developed in about 20 minutes, resulting in a visible purple coloration.
• 🕵️‍♂️ Developed fingerprints can be compared against suspect databases to aid in crime investigations.

Q & A

What is ninhydrin and its primary use in forensic science?

Ninhydrin is a chemical compound used in forensic science to develop fingerprints on paper by reacting with amino acids present in sweat.

How long has ninhydrin been used in law enforcement?

Ninhydrin has been used by law enforcement agencies around the world since 1954.

What happens to fingerprints when they come into contact with ninhydrin?

When fingerprints come into contact with ninhydrin, they turn purple due to a reaction between ninhydrin and the amino acids in the fingerprint residue.

What preparation is required before using ninhydrin for fingerprint development?

Before using ninhydrin, the solid compound must be dissolved in solvents to create a stock solution, which is then mixed with a carrier solvent to make a working solution.

What precautions are taken when handling evidence items in the process?

Technicians wear cotton gloves under nitrile gloves to prevent contamination of evidence items with any residues from their hands.

What is the process for applying ninhydrin to a fingerprint sample?

The sample is briefly immersed in the ninhydrin working solution, then allowed to drip dry before being placed in a development tray.

How long does ninhydrin usually take to develop fingerprints?

Normally, ninhydrin is allowed to develop for 24 to 48 hours, but it can be accelerated by placing the sample in an oven for 20 minutes.

What color indicates successful development of fingerprints using ninhydrin?

A beautiful purple color indicates that ninhydrin has successfully reacted with the amino acids in the fingerprint residue.

What can be done with the developed fingerprints?

The developed fingerprints can be compared to suspects in an identification database or further examined for criminal investigations.

Why is it important to avoid contamination during the fingerprint development process?

Avoiding contamination is crucial to ensure the integrity of the evidence and the accuracy of any comparisons made with suspect fingerprints.