Ninhydrin thiohemiketals: basic research towards improved fingermark detection techniques employing nano-technology

In the first part of a comprehensive research project towards more efficient application of nano-technology to fingerprint visualization, we investigated the possibility of more selective binding of gold nanoparticles (NP) to fingerprint material. We synthesized derivatives of ninhydrin and 1,2-indanedione containing loosely bound thiol groups. In particular: thiohemiketals (THK) of ninhydrin, and thioketals of 1,2-indanedione were prepared and tested as potential fingerprint reagents. By reacting ninhydrin with various thiols we were able to produce a series of novel THK, bearing the SR group always at C2. Ninhydrin THK reacted with amino acids to produce the expected Ruhemann's purple, and they also developed latent fingermarks on paper in a similar manner to ninhydrin. Ketals and thioketals derived from 1,2-indanedione reacted neither with amino acids nor with latent fingermarks. In the second part of the research, the thiols which are formed on the ridges as byproducts of the reaction with amino acids will be tested for their potential as stabilizers for gold NP that will become covalently bound to the fingerprint ridges.