In the study presented here, four examples of crime scene fingermarks analysed by Matrix Assisted Laser Desorption Ionisation Mass Spectrometry Imaging (MALDI MSI), in collaboration with the local Police Force, are reported. These marks are associated to high profile crimes such as drug dealing, murder and harassment. Following the application of forensic enhancement techniques by the CSI or the crime lab, one of the marks could be directly analysed on the surface of deposition and the others were analysed as primary lifts. In one case, no physical or molecular information was obtained whereas in two cases both ridge detail (albeit not useful for identification purposes) and molecular information could be retrieved. In one case, the intelligence gathered around the suspect's state of mind is, to date the most accomplished demonstration of the benefits and the operational feasibility MALDI MS based methods. These four casework examples are to be considered a first insight into the limitations, benefits and feasibility of MALDI MS based methods in the field; due to the extreme variability in the state of the mark, comprehensive evaluation of these aspects can only be undertaken upon the analysis of a large number of crime scene marks. However, this work does represent a significant advancement, compared to previous published work, as it demonstrates operational feasibility, with different levels of success, despite uncontrollable, unknown and unaccountable environmental and donor variability.

Expanded range of retrievable intelligence from fingermarks via MALDI MS based methods and increased operational capabilities of the technology.

In the last decade, Matrix Assisted Laser Desorption Ionisation Mass Spectrometry (MALDI MS) has proven to be a valuable analytical tool in forensic research as it can detect and map molecular information of forensic relevance in trace evidence such as fingermarks and hair. The first published proof of concept demonstrating that it was possible to differentiate males and females from the peptide and protein content of their fingermarks was published in 2012. In that work, MALDI MS was used in Profiling mode (MALDI MSP) to quickly obtain spectral profiles of ungroomed marks.

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Eight years of intensive research have demonstrated that Matrix-Assisted LaserDesorption/Ionisation Mass Spectrometry Profiling and Imaging (MALDI-MSI and MSP) are powerful tools to gather intelligence around a suspect lifestyle, directly from the identifying ridges of a latent fingermark. In the past three years, many efforts have been invested into translating laboratory methodologies to the field; this was undertaken by devising protocols either for (a) enabling initial fingermark visualisation, such as through the Dry-Wet method, recovery and subsequent MALDI MS based analysis, or for (b) rendering the MS methodologies compatible with the prior application of commonly employed fingermark enhancement techniques (FET). In the present work a major point of interest concerned the sample treatment of FET visualised-lifted fingermarks and the subsequent MS performance of primary tape lifted fingermarks ("primary lifts") versus secondary tape lifted fingermarks (recovery from the surface a second time following the initial primary lift). This was necessary since it may not always be possible to obtain primary lifts of marks visualised at crime scenes for remote MALDI-MSP and MSI. The work illustrated here has provided methodological insights into establishing how to best treat a few types of developed marks in preparation for MALDI-MSI when presented as both secondary and primary lifts; it was demonstrated, as expected, that primary lifts generally yield much higher quality chemical/physical information and are therefore crucial to maximise chances of suspect identification and of retrieval of chemical intelligence. When analysing secondary lifted marks that have been initially developed using aluminium or carbon powders, any of the trialled sample preparation methodologies can be employed except the Dry-Wet method. In the case of TiO 2 powder developed marks, the best ridge coverage was achieved by re-enhancing the mark using the initial powder and spray-coating with MALDI matrix. Primary lifts of fingermarks contaminated with an exogenous substance (used as a reference model) yielded the best ridge detail quality whilst for secondary lifts of natural marks pre-enhanced with aluminium powder, significantly greater intensity of the ion image was observed for the sections subjected to either no further enhancement or re-enhancement using aluminium powder.Keywords: Fingermarks; MALDI; Imaging; powders; lifts IntroductionWhile successful academic research is paramount for scientific progress, it is its translational feasibility that enables the impact of this research in the real world. With this view in mind, these authors are actively pursuing the development of protocols enabling MALDI-MS based technologies, with particular focus on the imaging modality, to be implemented into the current fingerprinting workflow.The pioneering development of MALDI-MS methodologies in fingermark analysis has a short but strong track record history of success, demonstrating the opportunity to retrieve additional devising an ...