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MALDI-MSI Imaging of Latent Fingerprints

This visualization technique enables greater resolution and contrast in fingerprint analysis.

For years, forensic scientists have been seeking new methods to improve existing techniques for the visualization of latent fingerprints. The structured combination of optical methods (diffused reflection, luminescence, UV absorption and reflection), physical methods (powdering, vacuum metal deposition, small particle reagent), physico-chemical methods (physical developer, multi-metal-deposition, iodine, cyanoacrylate), and chemical methods (ninhydrin and its analogues, DFO, etc.), permits a highly efficient processing of the secretions deposited by the fingers on a great variety of substrates. To visualize these developed fingerprints, alternative light sources or laser-based detection methods are commonly used. However, like all other existing techniques, these optical methods do not work in all possible cases, and certain types of latent fingerprints or object surfaces with unique characteristics may be problematic.

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) has been developed for visualization in which a UV pulsed laser rasters sequentially over a defined area of a sample while acquiring a mass spectrum from every location. From this array of spectra, analyte-specific images (molecular profiles) can be generated based on the selected masses, mapping precisely the analytes’ location on a surface.

To assess the possibility of fingerprint visualization with simultaneous chemical analysis based on MALDI-MSI, a model experiment was performed. Specifically, the finger of a 30-year-old man was lightly coated with ointment containing tocopherol and imprinted on a stainless steel MALDI plate. Application of low-concentrated tocopherol allows efficient laser ionization without use of matrices or additional treatment of the fingerprint. The result of the MS imaging scan shows that MALDI-MSI is a very promising analytical tool to be used in biometric research with good enough resolution and sensitivity, even for fast-mode of a scan.

The mass spectrometry method optimized for molecular peak and main fragments of tocopherol gave signal increase of over one order of magnitude. However, no clear fingerprint pattern was achieved for fingerprints without additives. The main reason is a lack of an efficient method for ionization, spectrometry, and data-processing of sweat components at this point. To develop improved mass spectrometry methods optimized for fingerprint scanning and signal enhancing, a better understanding of sweat component mass spectrometry was required.

As a result, the major objective of the second phase of this research was characterization of relevant biometry sweat components and MALDI-MS methods optimization. The most intensive, significant, and informative signal for fingerprint biometry applications can be attributed to 1.2 to 10.0 KDa mass range, which is characteristic for peptides and small proteins. A series of matrices and deposition techniques was evaluated for fingerprint signal enhancing in this mass range.

Another set of experiments was aimed to characterize previously described sweat compounds. For that purpose, collected sweat secretions were pre-concentrated and gel-filtrated through Sephadex G-10 Column to remove small molecules. MALDI-MS analysis of the concentrated sweat samples demonstrated features similar to the mass spectrum of the subject’s fingerprint.

This work was done by Bogdan Belgorodsky, Ludmila Fadeev, and Michael Gozin of Tel Aviv University for the Air Force Office of Aerospace Research & Development. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Physical Sciences category. AFRL-0173

Topics:
Anatomy Cartography Chemicals Education and training Emissions Exhaust emissions Ferrous metals Fluids and secretions Imaging and visualization Lasers Medical, health and wellness Medical, health, and wellness Metals Optics Particulate matter (PM) People and personalities Physical Sciences Research and development Steel
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MALDI-MSI Imaging of Latent Fingerprints

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    Magazine cover
    Defense Tech Briefs Magazine

    This article first appeared in the December, 2010 issue of Defense Tech Briefs Magazine (Vol. 4 No. 6).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document presents a research project aimed at developing a novel methodology for visualizing latent fingerprints while simultaneously conducting chemical analysis using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI). Conducted by Dr. Michael Gozin and his team at Tel Aviv University, the study focuses on the chemical composition of sweat, particularly compounds with molecular weights larger than 3,000 Da, from a diverse group of 30-40 adults.

    The introduction highlights the historical significance of fingerprint analysis in forensic science, noting its unique and invariable nature, which makes it a reliable biometric identifier. The increasing prevalence of identity fraud has amplified the need for advanced biometric technologies for personal identification in various applications, including access control and financial transactions.

    The methodology section details the collection and storage of sweat samples. The skin of the subject is cleansed with a 50% ethanol solution, and sweat is collected in a clean pouch over a 30-50 minute period. The collected samples are concentrated and purified using Sephadex G-10 Medium columns to remove small interfering substances, ensuring that the analysis focuses on the relevant chemical components.

    The results indicate that the MALDI-MSI technique is promising for fingerprint visualization, demonstrating good resolution and sensitivity even in fast-mode scans. A model experiment involved lightly coating a finger with tocopherol ointment before imprinting it on a stainless-steel MALDI plate. This approach allowed for efficient laser ionization without the need for additional matrixes or treatments, significantly enhancing the signal for the molecular peak of tocopherol.

    The findings suggest that MALDI-MSI can be a powerful analytical tool in biometric research, offering potential improvements in raw data processing for better resolution and contrast. The study underscores the importance of integrating chemical analysis with fingerprint visualization, paving the way for advancements in forensic science and biometric identification.

    Overall, this research contributes to the understanding of sweat composition and its implications for fingerprint analysis, highlighting the potential of MALDI-MSI as a dual-purpose tool in both forensic and non-forensic applications. The project is part of a broader effort to enhance biometric technologies, making them more reliable and effective in various identification scenarios.

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