MALDI-mass spectrometry imaging for touch chemistry biometric analysis: Establishment of exposure to nitroaromatic explosives through chemical imaging of latent fingermarks

Abstract

Fingerprint ridge patterns continue to be tremendously important in forensic science because of their power to identify individuals. However, the current emphasis on the patterns fails to take advantage of additional chemical information they contain that may have a bearing on an investigation. One way this information can be useful is through correlating the fingerprint pattern with the presence of compounds that suggest exposure to compounds of interest, such as energetic materials that can be used to create explosive devices. We report here how interrogation of fingermarks by MALDI-mass spectrometry imaging (MSI) can be used to expose the presence of the explosive compounds trinitrotoluene (TNT), tetryl and picric acid, while yielding the fingerprint pattern that is traditionally collected in crime scene investigation. Ion images derived from diagnostic [M−H]− ions at nominal m/z 226 and 228 for TNT and picric acid respectively, and the [M-NO2-H]− ion at m/z 241 for tetryl were generated and revealed the fingerprint pattern. Direct analysis in real-time high-resolution mass spectrometry (DART-HRMS) analysis of fingerprints was found to be useful in enabling rapid detection of diagnostic ions, so that their presence could inform whether subsequent MALDI-MSI experiments should be performed. The approach illustrates how DART-HRMS and MALDI-MSI in tandem can be employed in touch chemistry biometrics for revealing a direct connection between an individual and materials of forensic interest to which they have been exposed, such as explosives.