Lee Laboratory
for Biological Mass Spectrometry
Department of Chemistry
Iowa State University
Chemical imaging of latent fingerprints
Fingerprints have been used for forensic investigation over one hundred years, but it becomes useless if there is no match in FBI database search. Chemical information of fingerprints have been realized for its potential usefulness in forensic investigation, especially using mass spectrometry imaging. There have been many scientific publications in this regard in the last ten years, but it is still in lack of systematic study. Funded by National Institute of Justice, we are systematically studying its potential using MALDI-MSI.
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One such application is the aging of fingerprints. The time since deposition of fingerprints is critical as its deposition time is arguable as a court evidence. We demonstrated the use of chemical diffusion can be used as a measure of aging; however, the surface interaction is a key to determine the diffusion (O'Neill and Lee, J. Forensic Sc. 2018).
Exogeneous compounds on fingerprints have been previously studied to find crucial information about individuals, but mostly limited to explosives or illicit drugs. In our study, we demonstrated a range of exogenous fingerprint compounds can be detected that may reveal a personal lifestyle through chemical markers (Hinners et al. Scientific Reports, 2018). In a mock experiment shown below, multiplex MS imaging data acquisition was utilized to obtain hundreds of MS/MS spectra in a single data acquisition, which can be used for the identification of the compounds in addition to their precursor images. In this example, the two overlapped fingerprints are separated from the difference in chemicals, one contaminated by wine and the other by mandarin.
Compatibility of commonly used forensic development techniques with MALDI-MSI is important so that this technique can be widely used in forensic investigations. We have successfully demonstrated the compatibility of cyanoacrylate fuming (O'Neill et al., J. Forensic Sci., 2018), forensic carbon powder (Hinners and Lee, J. Forensic Sci., 2019), and iodine fuming/ninhydrin (King et al. in preparation). Particularly, forensic carbon powder is superior to traditional matrices and can be used without additional matrix (see figure below). Unlike previously reported, high-resolution mass spectrometry can clearly distinguish fingerprint chemicals from carbon clusters and produce clear MS images.
Mass spectrometry is well known as a destructive technique, but MALDI-MSI process is so gentle that there is no apparent changes after the data acquisition. As a result, the fingerprint can still be kept as a court evidence.
