Examination of Firearms Review: 2007 to 2010 - Interpol

Reinholz chose to target albumin, a protein constituting ca. 60% of the serum-protein
volume and secreted by the eccrine sweat glands (277). More precisely, given that
an “anti-human whole serum” was used, the whole serum constituents were actually
targeted, and not specifically the albumin. Fingermarks were left on five porous
substrates (i.e., white and manila envelopes, recycled paper, post-it, and
nitrocellulose), and aged from 15 to 130 days under artificial and natural light. Once
processed, purple fingermark ridges could be observed on a more or less clearer
background (depending on the substrate), with visible third-level details. It should be
noted that the detected marks progressively fade with time. Finally, the integration of
this technique in the existing detection sequences was assessed. A DFO-processed
fingermark (fresh mark on white paper) gave more details once subsequently
processed with the albumin recognition technique. However, when applied after
ninhydrin, the visible mark vanished and no detail could be further observed. Finally,
this procedure gave equivalent results when applied after physical developer. The
described procedure seems promising. Nevertheless, it is extremely time-consuming
and labour-intensive, with several blocking/staining and rinsing baths.
Drapel et al. identified and targeted three proteins present in the secretion residue
and implicated in the skin regeneration process (i.e., keratin, cathepsin, and
dermcidin) (276). Using a chromophoric enhancement process, positive results were
obtained on fingermarks left on PVDF (a substrate commonly used in biology to fix
proteins), but also on paper. Further research is currently performed, especially to
decrease the time required by the procedure (several hours) and to introduce
luminescent markers.
2.2.8 Detection of fingermarks on thermal paper
Some techniques specifically developed for thermal papers were
described or renewed: incorporation of polyvinylpyrrolidones in a ninhydrin
solution to avoid the darkening of the substrate (279), dry-application of
1,2-indanedione (280), use of heat and steam (281, 282), iodine fuming
(283), or vacuum metal deposition (282). The use of pDMAC to detect
marks on thermal papers was also assessed (227), with the conclusion
that classical amino acid reagents are better choices.
In the previous report (284), we mentioned the “solution G3” as a powerful posttreatment
for ninhydrin- and DFO-processed thermal papers whose reactive layer
could have darkened due to the polar solvents contained in the reagent solutions
(285). Recently, Schwarz & Klenke proposed a modified ninhydrin formulation
containing polyvinylpyrrolidones (PVP) (279). The introduction of PVP in the working
solution prevents the darkening of the thermal layer, and allows a one-step detection
of fingermarks which readily appear in clear contrast with the background. PVP being
nontoxic and reasonably priced, it could constitute a promising alternative to the
existing two-steps discolouration procedure. One drawback of the currently proposed
formulation is the ratio of polar solvent (compared to non-polar ones) that could
cause ink running in particular cases. Further research is still undergoing, especially
about the possibility to include PVP in DFO or 1,2-indanedione working solutions.
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