Alpha-Amino Acids
Definition
Molecules bearing an amine group on the carbon adjacent to the carboxyl group; the primary molecular target of ninhydrin, DFO, and indanedione in eccrine latent print residue on porous surfaces.
- Structural feature
- Amine group on carbon next to carboxyl
- Reagent targets
- Ninhydrin, DFO, indanedione
- Source in print
- Eccrine sweat residue
- Surface type
- Porous substrates
Common questions
Why do these reagents work well on paper but not on plastic or metal?+
Ninhydrin, DFO, and indanedione all need to diffuse into the substrate and react with amino acids that have been absorbed into the fiber structure, which porous materials like paper allow but non-porous surfaces do not, since residue there sits on top rather than soaking in.
What is the practical difference between ninhydrin and DFO or indanedione results?+
Ninhydrin gives a visible purple product readable in ordinary light, while DFO and indanedione produce reaction products that fluoresce under specific excitation light and generally give greater sensitivity, so they are often applied in sequence rather than as interchangeable alternatives.
Related terms
- DFO (1,8-Diazafluoren-9-One)
- A fluorescent ninhydrin analogue used for latent fingerprint development on porous surfaces; excite at 450-470 nm (with secondary absorption extending into the...
- HFE (Hydrofluoroether)
- A class of solvents used as carriers for ninhydrin, DFO, and indanedione formulations; lower toxicity and flammability than older acetone or ethanol...
- Indanedione-Zinc
- A fluorescent amino acid reagent (indane-1,3-dione complexed with zinc chloride) that produces an orange-yellow fluorescent product; reported to be more sensitive than...
- Ninhydrin
- A chemical reagent (2,2-dihydroxyindane-1,3-dione) that reacts with alpha-amino acids in latent print residue to produce a purple-blue compound (Ruhemann's Purple); the primary...
- Physical Developer (PD)
- A multi-bath silver-deposition wet-chemistry method that deposits silver metal onto fatty latent print residue on porous surfaces; the only technique that recovers...
- Ruhemann's Purple
- The purple-blue condensation product formed when ninhydrin reacts with alpha-amino acids; the visible development indicator used in latent fingerprint examination on paper...
- Sequential Processing
- The application of chemical development methods in a fixed, evidence-preserving order that maximises cumulative recovery while preventing earlier treatments from destroying the...
- Treatment Log
- The contemporaneous written record of every chemical method applied to an item of evidence, including reagent batch, examiner identity, date/time, and result;...
- Vacuum Metal Deposition (VMD)
- A technique in which gold and zinc are sequentially evaporated in a vacuum chamber; the gold deposits uniformly while zinc nucleates differentially...