Hidden signatures: new reagents for developing latent fingerprints.

Aldehydes substituted with a quaternised pyridinium or quinolinium ring have been investigated for the development of latent fingerprints. Two routes were developed to a novel in situ formed azacyanine dye. This dye might form in the fingerprint where reagents are concentrated but does not form appreciably in solution experiments as evidenced by the lack of an absorption band at 600 nm. N-Alkyl and N-aryl substituted benzimidazole-2-carboxaldehydes give stable fluorescent fingerprints.