Forensic visualisation of blood and blood provenance in old fingermarks by MALDI MS Imaging

Significance of the Topic

Blood detection and provenance in fingermarks is a cornerstone of forensic investigation since it enables reconstruction of crime dynamics and distinction from other biofluids

Objectives and Study Overview

This study aimed to visualize and differentiate human and animal blood in four year old latent fingermarks using matrix assisted laser desorption ionisation mass spectrometry imaging combined with bottom up proteomics

Methodology

In situ tryptic digestion was performed on dried human and bovine blood fingermarks with nine layers of trypsin at 200 micrograms per milliliter containing 0.1 percent surfactant followed by five layers of matrix application using alpha cyano 4 hydroxy cinnamic acid in organic solvent

Used Instrumentation

• timsTOF fleX mass spectrometer operating in the m/z range 100 to 3000 with a lateral resolution of 50 micrometres
• SciLS Lab software for image processing and root mean square normalisation
• SunCollect sprayer for matrix and enzyme deposition

Main Results and Discussion

MALDI MSI successfully visualised haemoglobin alpha and beta chain peptides in a four year old human blood fingermark, revealing ridge flow even in areas not visible by optical inspection. Additional human specific proteins such as haptoglobin serotransferrin and erythrocyte band protein 4 were mapped albeit at lower abundance. Lipid imaging at selected m/z values provided enhanced ridge coverage complementing protein signals. For the first time bovine blood biomarkers including myoglobin and glyceraldehyde 3 phosphate dehydrogenase peptides were imaged in aged fingermarks demonstrating clear species level discrimination. The study highlighted the influence of local enzyme to substrate ratio on signal distribution

Benefits and Practical Applications

• Provides confirmatory evidence of blood presence beyond presumptive tests at crime scenes
• Enables discrimination between human and animal blood down to species
• Yields ridge detail in latent fingermarks otherwise unsuitable for biometric identification
• Applicable to aged samples recovered long after the event

Future Trends and Applications

Advances may include integration of combined protein and lipid imaging workflows portable mass spectrometry for in field applications improved matrix deposition methods for higher sensitivity and spatial resolution expansion to other biofluids and molecular markers and automation for forensic laboratory pipelines

Conclusion

The application of high resolution MALDI MSI on aged fingermarks demonstrates robust detection imaging and species attribution of blood biomarkers while reconstructing ridge detail, thereby offering a powerful confirmatory tool for forensic investigations

References

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