Examination of Firearms Review: 2007 to 2010 - Interpol

(CdSe) QDs were synthesized and used to detect fresh marks on the adhesive
surface of tape and promising results were obtained (262). Cadmium telluride (CdTe)
QDs, synthesised in aqueous solution, were used to detect blood fingermarks on
various nonporous surfaces such as aluminium foil, black polyethylene, glass or
transparent polypropylene (265). A comparison with acid yellow 7, one of the best
blood reagents for non-porous substrates, showed that the QDs were superior to acid
yellow 7 on aluminium and equally effective for the other substrates. The immersion
of a sample in an aqueous CdTe solution has also been proposed to detect
fingermarks on non-porous substrates (263, 264). Several hours of immersion were
however necessary, which constitutes too long a time. The embedment of QDs in a
polyamidoamine dendrimer (PAMAM) has been successfully applied to enhance the
contrast of fumed fingermarks on non-porous surfaces (266, 267). Nevertheless, an
immersion time of several hours is required which is still much too long. As can be
seen, the use of QDs to detect fingermarks currently remains a research topic and no
casework uses of QDs have been reported yet. Some issues remain to be addressed
before routine application, like the toxicity of cadmium and improved targeting of
secretion residues by functionalization of the QD outer surface.
Silica nanoparticles
Silica nanoparticles constitute another kind of promising nanocomposites to detect
fingermarks since a great freedom is offered in terms of outer functionalization and
dye-doping. The use of luminescent silica nanoparticles for forensic purposes
somewhat still remains at the pilot study stage. Theaker et al. recently reported
entrapment of a variety of coloured and fluorescent dyes including basic red 28,
basic yellow 40, fluorescein, methylene blue, oxazine perchlorate, rhodamine B,
rhodamine 6G and thiazole orange within silica particles (256). The resulting doped
nanoparticles were used in aqueous suspensions to detect fingermarks. The process
is very similar to that described for small particle reagents. Micron-size particles also
were used as dusting agents. Both fresh (20-minute-old) and aged fingermarks (40day-old)
showed good definition after development. Liu et al. entrapped an europiumbased
dye inside silica nanoparticles and further powdered the obtained
nanocomposites to detect fresh and six-day-old latent fingermarks on various
substrates (e.g., plastic bag, rubber glove, coloured paper, and green leaf) (257).
Silica nanoparticles doped with carbon black have also been used as a fingerprint
powder to detect fingermarks on glass and metal surfaces, before being lifted using a
lifting tape (258-260). The originality of this work lies in the fact that the dusted marks
were further imaged using surface assisted laser desorption / ionisation - time of
flight - mass spectrometry (SALDI-TOF-MS). By doing this, it has been possible to
differentiate fingermarks left by smokers (or drug users) from fingermarks left by nonsmokers,
the silica nanoparticles performing as effective ionisation / desorption
agents for the analysis of the drugs and metabolites contained in the secretion
residue.
Other nanoparticles
Sodhi & Kaur chose to coat aluminium oxide nanoparticles with two different
molecules: Lucifer Y (a fluorescent dye) and a natural hydrophobic substance (268).
Their aim was to obtain a “nanopowder” to be dusted on substrates and
characterized by an enhanced ability to detect fingermarks through lipophilic
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