Abstract
•ToF-SIMS can visualise VMD developed fingerprints on glass, PET and PVC substrates.•ToF-SIMS can visualise ridge detail on PET and PVC in voids left by VMD development.•ToF-SIMS can overcome optical background interference, for example over ink lines.
In forensic laboratories, a common and versatile process to develop fingerprints is vacuum metal deposition (VMD). In some instances, however, it creates the phenomenon of ‘empty prints’, where the only development on the surface is outside of the fingerprint area, yielding no ridge detail. Previous work has shown that Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) can enhance fingerprint recovery after ninhydrin, black powder suspension or cyanoacrylate stained with basic yellow 40 (standard processes used by forensic laboratories) on paper, stainless steel and polyethylene surfaces. ToF-SIMS has not yet been compared in sequence with VMD on non-porous surfaces. In particular, it has not been assessed to see if ridge detail can be enhanced following VMD development.
This study aims to further inform forensic practitioners of when and how to incorporate ToF-SIMS into the fingermark development workflow. The main focus of the study is to assess the suitability of ToF-SIMS to enhance fingerprints deposited on two surfaces commonly problematic for VMD: polyethylene terephthalate (PET) and polyvinyl chloride (PVC). In this work, a fingerprint expert compared the friction ridge detail developed by VMD to the ridge detail after ToF-SIMS enhancement. Fingerprints were deposited on glass, PET and PVC, developed with VMD and then enhanced with ToF-SIMS. This work demonstrates that ToF-SIMS is compatible with VMD in sequential processing. Overall, in >83 % of samples, the ridge detail produced by ToF SIMS was at least equivalent to VMD. Importantly, ToF-SIMS was able to visualise ridge detail on all samples where VMD gave ‘empty prints’ or no visible development, which was on 75 % of all PVC samples. ToF-SIMS also overcame some background interferences (such as ink) that affected optical imaging of fingerprints following VMD.