The influence of storage conditions on fingermarks developed with 1,2-indanedione-ZnCl.

The most important class of reagents for the enhancement of fingermarks on porous surfaces are those that react with the amino acid constituents of fingermarks. Ninhydrin, DFO (1,8-diazafluoren-9-one), and 1,2-indanedione are the three most common techniques widely known in forensic laboratories for the visualization of latent fingermarks on porous surfaces. In 2012 the Netherlands Forensic Institute replaced DFO by 1,2-indanedione-ZnCl after an internal validation, just like an increasing numbers of laboratories. In 2003, Gardner et al. published an article showing that fingermarks treated with 1,2-indanedione (without ZnCl), that were stored in daylight only decreased by 20% in fluorescence in 28 days. However, during casework we observed that the fluorescence of fingermarks treated with 1,2-indanedione with ZnCl decreased more rapidly. In this study, the effect of various storage conditions and aging times on the fluorescence of marks after treatment with 1,2-indanedione-ZnCl were assessed. Latent printed fingermarks from the digital matrix printer (DMP) and natural fingermarks from a known donor were used. The results showed that storing fingermarks in daylight (wrapped and un-wrapped) drastically decrease (over 60% loss) in fluorescence in approximately three weeks. Storage of the marks in a dark environment (at room temperature, in the refrigerator or even in the freezer) resulted in a decrease in fluorescence of less than 40%. Our recommendation is to always store treated fingermarks with 1,2-indanedione-ZnCl in a dark environment and, if possible, photographing them directly (within 1-2 days after treatment) to minimize the decrease of fluorescence.

Positive control tests for fingermark development reagents.

At the start of this study, no reliable, consistent, challenging and representative positive control test was commercially available for fingermark visualisation techniques. The goal of this study was to determine the lower limits of detection (LOD) of the fingermark visualisation techniques ninhydrin and 1,2-indanedione-ZnCl and developing positive control tests for these techniques. Spot tests with an amino acid solution were produced to determine the lower LOD's. Secondly, a Dimatix Materials Printer (DMP) was used to print simulated fingermarks using different concentrations of an amino acid solution, to determine the lower LOD of ninhydrin and 1,2-indanedione-ZnCl using the DMP. Concept positive control tests were developed using the lower LOD of ninhydrin and 1,2-indanedione-ZnCl. These were later on adjusted, to form the definitive positive control tests, after a testing period of two months.