Abstract:
This study investigated the use of UV-visible spectral imaging for the location and
enhancement of substances of forensic interest using targeted approaches based on the
spectrum of the substance.
Spectral enhancement procedures were developed for blood with and without chemical
enhancement, and for latent fingermarks after chemical enhancement. Focus was on
substances whose spectrum exhibited a steep change in absorbance or fluorescence
over a small wavelength range. Substances with such spectral features were able to be
enhanced using arithmetic combinations of two or three spectral images taken at
wavelengths near the steep spectral feature.
Some enhancement reagents do not react to produce a product with a steep spectral
feature suitable for photographic enhancement. In such cases reagents that compliment
spectral imaging can be developed. A tridentate ligand for iron(II), BBIDMAPP,
which forms a complex with a narrow intense charge-transfer band, was synthesised
and was used to visualise muddy shoemarks.
UV-visible spectral imaging systems based on a liquid crystal filter or a filter wheel
were constructed to facilitate the acquisition of the spectral images and to perform the
enhancement operations. A thorough characterisation of the imaging systems
determined their limitations and sources of artefacts which could lead to complications
in interpreting the enhanced images.
The spectral imaging procedure used to visualise blood was incorporated into a
near-real-time, hand-held imaging system for the location of blood staining. This
prototype imaging system is capable of acquiring two spectral images simultaneously,
perform the enhancement procedure, and display the enhanced image within 5 s, which
would make it suitable as a non-chemical presumptive screening test for blood at crime
scenes.