A fingerprint examiner identifies a latent print on a glass surface. The print was made by a secretion from eccrine sweat glands. The examiner uses a reagent that reacts with amino acids in the sweat residue to produce a purple coloration (Ruhemann's purple). Which reagent is being used?
- A Ninhydrin ✓
- B Sudan Black
- C 1,8-Diazafluoren-9-one (DFO)
- D Crystal violet
Explanation
Ninhydrin reacts with free amino acids (principally lysine and its metabolites) in eccrine sweat residue to produce Ruhemann's purple — a vivid purple chromophore. It is the primary chemical method for developing latent fingerprints on porous surfaces (paper, cardboard). DFO (1,8-diazafluoren-9-one) also reacts with amino acids but produces a fluorescent product best visualised under blue-green light; it is used before ninhydrin to maximise ridge detail. Sudan Black reacts with fatty residues and is used mainly on non-porous surfaces. Crystal violet (gentian violet) is used to develop prints on adhesive surfaces.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.