Fingerprints have been studied for uniqueness, identification and criminal importance for more than one hundred years. The significance of fingerprints and the criminal justice system can’t be undervalued; they can implicate the guilty by linking a criminal to the victim and the scene of the crime and exonerate the innocent. Through technology and expertly trained fingerprint examiners, the fingerprint can be the single most important piece of evidence for solving a crime.
Fingerprints can be located and collected from three main groups: plastic fingerprints caused by a negative three-dimensional impression such as clay or wet paint, fingerprints contaminated with foreign matter such as blood or dust, and latent prints that is generally not visible to the naked eye and must be developed by one of various developing techniques.
Latent fingerprints left on a porous surface such as paper is usually detected by a chemical process called ninhydrin. Ninhydin reacts to the amino acids secreted by the fingers and turns the invisibles fingerprints dark purple. I’ve used this process to develop fingerprints on an anonymous letter sent to a victim. The process takes several hours to develop. And yes, the fingerprints were definitely matched to the perpetrator who was already in prison.
Ninhydrin is an irritant and scientists are looking for a safer alternative. Simon Lewis and colleagues at Curtin University of Technology in Australia have found a compound in henna that can work in a similar way to ninhydrin without causing irritation. Henna is derived from the plant Lawsonia inemis and has been used for skin care, hair dye, and cosmetics without any ill effects for centuries.
Lawson is the compound thought to be responsible for the staining properties of henna. It has been found that the compounds react to the amino acids of invisible (latent) fingerprints. The result is a brown-purple color and is strongly luminescent under a forensic light source.
Research is currently under way along with new possibilities that may lead to improvements in fingerprint detection. Nature is truly amazing and shouldn’t be underestimated. I believe that most scientific answers can be found from nature.