Examination of Firearms Review: 2007 to 2010 - Interpol

Zhang et al. showed that it was possible to chemically image multimetal deposition
(MMD)-enhanced fingermarks using a scanning electrochemical microscope (SECM)
(358-360). This method is based on the measurement of the redox activity on a
localized area through to the solubilisation of silver. Since silver is preferentially
reduced on the gold nanoparticles, themselves located on papillary ridges, it was
possible to visualize the ridge details by scanning fingermarks processed by MMD.
This method could help visualizing classical MMD results on dark or patterned
substrates. Alternatively, SECM can also be used on silver-stained or benzoquinonetagged
fingermarks (361). However, SECM imaging needs to be optimized to enlarge
the scanning area and to reduce the time required to perform a scan before it could
be applied in casework.
Full-field swept-source optical coherence tomography was applied to image latent
fingermarks left on semi-reflecting glass (363). This technique provides information
about tomography as well as topography of the marks. According to the authors, the
detection of very poor quality marks as well as old ones, buried beneath dust layers,
is possible. Reconstructed ridge details are however not as clear as it should be, and
the scanned area is smaller than the size of a single fingermark.
The application of desorption electrospray ionization - mass spectroscopy (DESI-MS)
was described (365). A solvent was electro-sprayed on the surface bearing the
sample to be analyzed, generating secondary scattered droplets that are further
evaporated and analyzed by MS for each point of the surface (spatial resolution: 150
µm, scanned area: 19.2 x 14.8 mm²). This method gives chemical information,
associated with the ridge pattern of the fingermark. For this study, fingertips were
contaminated with drugs and explosives in solution, before being pressed on glass,
paper and plastic. Good ridge details were obtained, also on tape-lifted marks that
were analyzed by the same technique.
Time-resolved luminescence imaging of cyanoacrylate-fumed fingermarks stained
with an europium-based dye could be used to circumvent the problems caused by
luminescent substrates (366). This technique took benefit of the long-lived europiumbased
dye luminescence (micro- to milli-seconds) compared to the short-lived
background luminescence (nanoseconds). The recording of the image has to take
place a short time after the excitation source has been shut down. As a result, the
unwanted background luminescence (or security features) is no more visible, and
fingermarks can be visualized with a good contrast. Illustrations are given for latent
fingermarks left on aluminium foil and plastic with security features.
A diffractive glossmeter sensor is presented as a new imaging technique to visualize
latent fingermarks left on glossy, curved objects (364). This technique gives
information about the local gloss of the ridges, depending on the local surface
roughness and refractive index. By rotating the item (i.e., a ballpoint pen in this case)
in front of the light source, it was possible to analyze the reflected light coming from
the scanned area. As a result, latent fingermarks were imaged and coloured
according to the strength of light reflection.
Time-of-flight - secondary ion mass spectrometry (ToF-SIMS) was applied to image
and analyze drug-contaminated fingermarks (368). For this study, washed fingertips
were contaminated with drug powder (i.e., amphetamine, methamphetamine, and
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