Staining of Fingerprints on Checks and Banknotes Using Ninhydrin

Latent fingerprints on paper and other porous surfaces can be developed using chemical methods so that they become visible to the naked eye and available as forensic evidence (
1
,
2
). Ninhydrin is the most commonly used reagent for developing fingerprints as it reacts with amino acids present in ecrine sweat to give the strong purple color familiar when it is used as a stain for protein. Another compound used is 1,8-diazafluorene-9-one (DFO), which gives fingerprints that fluoresce, and is claimed to be more sensitive. Paper evidence, such as checks and banknotes, are treated by immersing the paper in a tray of a solution of the reagents and allowing to dry. The solution can also be brushed onto cardboard or wallpaper. The latent fingerprints are then developed by heating the paper in a specially adapted oven at 80�C and 65% relative humidity. DFO-treated surfaces, however, are treated at 100�C with no added humidity (
3
).