Suspect identification by blood fingerprints using MALDI MS

In a prime crime scene, forensic investigation involves collection of fingerprints, any blood stains, residuals or other materials. As the first line of investigation DNA profiling can be used to identify the perpetrator or to establish foul play in a murder inquiry without a body. However, DNA amplification, profiling and matching may not always be possible depending on initial DNA quantity, degradation possibility, presence of a mixture and the existence of a record in DNA databases. Although only of an associative type, blood typing or detection of drugs or medications in a bloodstain or a blood fingermark may be important to an investigation.

Vital information of the blood proteins can be used in intelligence by testing the presence of heamoglobin variants [Hb variants (Hb var)] in blood samples. It could be beneficial to narrow down the pool of suspects, depending on their incidence and occurrence in certain geographical areas or linked to the inhabiting multi-ethnic population.

In healthcare, there are a number of techniques that are currently used to screen for Hb variants including cation exchange HPLC, tandem mass spectrometry, acid and alkaline gel electrophoresis (or isoelectric focusing electrophoresis), capillary zone electrophoresis and molecular methods, depending on the target of the screening. Depending on laboratories, combination of such techniques is employed to detect the variants. But the limitation includes of long analytical experiments and also destruction of evidence (as it is subjected to extraction).

Recent technologies like RapifleX (MALDI TOF/TOF) and timsTOF fleX supported with software like SCiLSlab can be a boon for identification. A study reveals that it could detect 6 heamoglobin varaints of heamoglobins like HbC, HbD-Iran, HbD-Punjab/Los Angeles, HbE, HbJ Baltimore and HbS. It has been investigated to evaluate the possibility to detect the six selected haemoglobin variants in blood and to visualise them in blood fingermarks. The use of these technologies has shown that, whilst the highest sensitivity is required to detect (and map) the Hb var under investigation.

timsTOF fleX is one a kind platform which allows measurement of wide range of molecules and its imaging in 4D without stopping, changing, modifying or compromising on results. It is a fully functional high speed, high sensitivity ESI instrument for all Omics analyses, combined with a high spatial resolution MALDI source and stage specifically designed for resolving molecular distributions and bringing a spatial dimension to Omics analyses. In the study of heamoglobin variants, timsTOF fleX proved to be a suitable technique to recover this type of intelligence from blood. The opportunity to detect and map Hb var could provide associative evidence to narrow down the pool of suspects during an investigation. timsTOF fleX identified most of the variants in 8 samples out of 9 with mass accuracies ranging between -3.2 to 3.1 ppm.

Even though the result looks promising, additional research with regards to detectability of other variants to fully understand Hb var, indication of ethnicity as well as geographical attribution based on different environmental conditions and evidence age are yet to be optimized to make this a practise of forensic setting.