Ninhydrin

DescriptionNinhydrin is historically the most common reagent for processing fingerprints on porous substrates. It has been used as a fingerprint reagent since the 1950s but has been used as a cell stain since the early 1900s. Ninhydrin molecules form a complex with amino acids resulting in a purple product known as Ruhmann's purple. Purple fingerprints are easily visible on light-colored porous substrates but may be difficult to see on patterned or dark-colored substrates. DFO reacts with amino acids to produce a fluorescent product that is not readily seen with the naked eye. This makes it a useful reagent on dark or patterned porous items. DFO prints are viewed with an alternate light source or laser set to 530–570 nm (green light) through a red barrier filter. 1,2-indanedione is an emerging fingerprint reagent that results in visible pink fingerprints that are also fluorescent. The fluorescence is viewed under the same conditions as DFO. These chemicals can be used on their own or in sequence to develop latent prints on porous substrates. If they are used in sequence, they are used in the following order: indanedione, DFO, ninhydrin. If a reagent is used out of sequence, it will inhibit or limit the effectiveness of the other reagents. In this laboratory exercise you will develop fingerprints on a porous substrate using indanedione, DFO, and ninhydrin. ninhydrin structure

HistoryNinhydrin was discovered in 1910 by the German-English chemist Siegfried Ruhemann (1859–1943). In the same year, Ruhemann observed ninhydrin's reaction with amino acids. In 1954, Swedish investigators Oden and von Hofsten proposed that ninhydrin could be used to develop latent fingerprints.

UsesNinhydrin is used for the detection of free amino groups in amino acids, peptides and proteins.

UsesNinhydrin is an amino acid-sensitive reagent for the development of latent fingermarks on porous surfaces. More sensitive alternatives, such as DFO and IND-Zn, are now available and these have advantages on porous substrates that are not highly luminescent. However, ninhydrin can still be applied after these treatments and may reveal additional ridge detail, particularly on highly luminescent substrates where luminescence visualization may be problematic.

General DescriptionWhite to light yellow crystals or powder. Becomes anhydrous with reddening at 257-266°F.

DefinitionChEBI: Ninhydrin is a member of the class of indanones that is indane-1,3-dione bearing two additional hydroxy substituents at position 2. It has a role as a colour indicator and a human metabolite. It is a member of indanones, a beta-diketone, an aromatic ketone and a ketone hydrate.