Identification of suspects via fingermark analysis is one of the mainstays of forensic science. The success in matching fingermarks, using conventional fingermark scanning and database searching, strongly relies on the enhancement method adopted for fingermark recovery; this in turn depends on the components present in the fingermarks, which will change over time. This work aims to develop a robust methodology for improved analytical detection of the fingermark components. For the first time, matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) has been used to image endogenous lipids from fresh and aged, groomed and ungroomed fingermarks. The methodology was initially developed using oleic acid which was detected along with its degradation products over a 7-day period, at three different temperatures in a time-course experiment. The optimised methodology was then transferred to the imaging analysis of real fingermark samples. Fingermark patterns were reconstructed by retrieving the m/z values of oleic acid and its degradation products. This allowed the three aged fingermarks to be distinguished. In order to prove that MALDI-MSI can be used in a non-destructive way, a simple washing protocol was adopted which returned a fingermark that could be further investigated with classical forensic approaches. The work reported here proves the potential and the feasibility of MALDI-MSI for the forensic analysis of fingermarks, thus making it competitive with other MSI techniques such as desorption electrospray ionisation (DESI)-MS. The feasibility of using MALDI-MSI in fingermark ageing studies is also demonstrated along with the potential to be integrated into routine fingermark forensic analysis.

Matrix deposition is a crucial aspect for successful matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) analysis. The search for more efficient protocols over the years has resulted in the devising of "dry matrix methods" in which the matrix is solely or preliminarily deposited as powder and acts in most cases as a seeding agent. Although not fully embraced by the MALDI MSI community, these methods have proven to be more efficient in terms of ion intensity, ion abundance, and ion images in the experimental circumstances they were employed. Here we report a novel two-step matrix application method, that we have named the "dry-wet" method, where the matrix is dusted onto the sample followed by solvent spray using a robotic device. The new method has been successfully applied to the detection and mapping of several analyte classes within latent fingermarks. Dusting the matrix generated the added advantage of enhancing the latent fingermarks which are invisible. This allows not only for an optical image to be taken of the fingermark in situ but also bridges the gap in the application of MALDI MSI technology in this field; with the use of the methodology reported, fingermark enhancement, recovery, and analysis from different surfaces is now compatible with subsequent MALDI MSI analysis thus allowing visual and chemical information to be obtained simultaneously.

After over a century, fingerprints are still one of the most powerful means of biometric identification. The conventional forensic workflow for suspect identification consists of (i) recovering latent marks from crime scenes using the appropriate enhancement technique and (ii) obtaining an image of the mark to compare either against known suspect prints and/or to search in a Fingerprint Database. The suspect is identified through matching the ridge pattern and local characteristics of the ridge pattern (minutiae). However successful, there are a number of scenarios in which this process may fail; they include the recovery of partial, distorted or smudged marks, poor quality of the image resulting from inadequacy of the enhancement technique applied, extensive scarring/abrasion of the fingertips or absence of suspect's fingerprint records in the database. In all of these instances it would be very desirable to have a technology able to provide additional information from a fingermark exploiting its endogenous and exogenous chemical content. This opportunity could potentially provide new investigative leads, especially when the fingermark comparison and match process fails. We have demonstrated that Matrix Assisted Laser Desorption Ionisation Mass Spectrometry and Mass Spectrometry Imaging (MALDI MSI) can provide multiple images of the same fingermark in one analysis simultaneous with additional intelligence. Here, a review on the pioneering use and development of MALDI MSI for the analysis of latent fingermarks is presented along with the latest achievements on the forensic intelligence retrievable.

An increase in the use of condoms by sexual offenders has been observed. This is likely to be due both to the risk of sexually transmitted diseases and to prevent the transfer of DNA evidence. In this scenario the detection of condom lubricants at a crime scene could aid in proving corpus delicti. Here we show a novel application of Matrix-Assisted Laser Desorption/Ionisation Mass Spectrometry Imaging (MALDI MSI) for mapping the fingermark ridge pattern simultaneously to the detection of the condom lubricant within the fingermark itself. Two condom brands have been investigated to prove the concept. Condoms were handled producing lubricant-contaminated fingermarks. Images of the ridge pattern were obtained simultaneously to the detection of two lubricants, even several weeks after the fingermark deposition. The results therefore show the potential of MALDI MSI to link the suspect (identification through fingermark ridge pattern) to the crime (detection of condom lubricant) in one analysis. This would enable forensic scientists to provide evidence with stronger support in alleged cases of sexual assault.

Despite the proven capabilities of Matrix Assisted Laser Desorption Ionisation Mass Spectrometry (MALDI MS) in laboratory settings, research is still needed to integrate this technique into current forensic fingerprinting practice. Optimised protocols enabling the compatible application of MALDI to developed fingermarks will allow additional intelligence to be gathered around a suspect’s lifestyle and activities prior to the deposition of their fingermarks while committing a crime. The detection and mapping of illicit drugs and metabolites in latent fingermarks would provide intelligence that is beneficial for both police investigations and court cases. This study investigated MALDI MS detection and mapping capabilities for a large range of drugs of abuse and their metabolites in fingermarks; the detection and mapping of a mixture of these drugs in marks, with and without prior development with cyanoacrylate fuming or Vacuum Metal Deposition, was also examined. Our findings indicate the versatility of MALDI technology and its ability to retrieve chemical intelligence either by detecting the compounds investigated or by using their ion signals to reconstruct 2D maps of fingermark ridge details.