Abstract
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•The hydrophobicity of the dye plays a significant role for developing fingerprints.•The fingerprints detection is also influenced by the chemical structure of the dye, hydrogen bonds, and interactions with solvents.•Nile red and Nile blue detect fingerprints with excellent to acceptable definition due to the great hydrophobicity.•Highly hydrophobic benzophenoxazine derivatives could be considered dual-fingerprint reagents because they develop luminescent and visible fingerprints.•Less hydrophobic benzophenoxazine derivatives or hydrophobic derivatives containing interference substituents develop weak luminescent fingerprints.
In this report, two classes of benzophenoxazine dyes, Nile red and Nile blue derivatives, were evaluated for the detection of latent fingerprints on porous surfaces. The efficiency to develop fingerprints is influenced by the physical properties of the dye molecules including hydrophobicity as characterized by distribution coefficient value (logD), and other factors such as chemical structure of the dye and hydrogen bonds. Both Nile red and the basic form of Nile blue showed excellent to acceptable ability to detect fingerprints due to their great hydrophobicity at 515 and Crime Scene Search (CSS) settings of the forensic light source. Higher hydrophobicity derivatives of Nile red and Nile blue (in the basic form) improved both quality and sensitivity of fingerprint detection in comparison with their corresponding parent dyes. They developed strong luminescent and visible fingerprints, and a better contrast was achieved between impressions and the background surface suggesting the potential use of these compounds in forensic investigation. Therefore, the hydrophobic derivatives are considered dual-fingerprint reagents because the developed prints can be seen by the naked eye and under illumination process. However, lower hydrophobicity derivatives of Nile red and Nile blue and derivatives with different substituents developed weak or non-luminescent fingerprints with poor contrast. A complete analysis of what dye properties are the most important in fingerprint detection is discussed along with dye optimization for improved performance.