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Page count: 11

The reaction product of ninhydrin with amino acids reacts further with europium chloride hexahydrate (EuCl3 · 6H2O) to form an organo-rare earth complex which exhibits Eu3+ luminescence at 615 nm with a lifetime of 0.4 ms. This emission is sensitized by intramolecular ligand to europium resonance energy transfer. Benzo(f)ninhydrin is better suited to this energy transfer process than ninhydrin and yields more intense Eu3+ emission. The emission is effectively excited by argon-ion laser near-ultraviolet (UV) light, which can be modulated such that time-resolved imaging can reveal amino acids on strongly fluorescent surfaces which would otherwise not be tractable. This is applied to the detection of latent fingerprints.