Fingermark initial composition and aging using Fourier transform infrared microscopy (μ-FTIR)

Abstract

This study investigated fingermark residues using Fourier transform infrared microscopy (μ-FTIR) in order to obtain fundamental information about the marks' initial composition and aging kinetics. This knowledge would be an asset for fundamental research on fingermarks, such as for dating purposes. Attenuated total reflection (ATR) and single-point reflection modes were tested on fresh fingermarks. ATR proved to be better suited and this mode was subsequently selected for further aging studies. Eccrine and sebaceous material was found in fresh and aged fingermarks and the spectral regions 1000-1850cm(-1) and 2700-3600cm(-1) were identified as the most informative. The impact of substrates (aluminium and glass slides) and storage conditions (storage in the light and in the dark) on fingermark aging was also studied. Chemometric analyses showed that fingermarks could be grouped according to their age regardless of the substrate when they were stored in an open box kept in an air-conditioned laboratory at around 20°C next to a window. On the contrary, when fingermarks were stored in the dark, only specimens deposited on the same substrate could be grouped by age. Thus, the substrate appeared to influence aging of fingermarks in the dark. Furthermore, PLS regression analyses were conducted in order to study the possibility of modelling fingermark aging for potential fingermark dating applications. The resulting models showed an overall precision of ±3 days and clearly demonstrated their capability to differentiate older fingermarks (20 and 34 days old) from newer ones (1, 3, 7 and 9 days old) regardless of the substrate and lighting conditions. These results are promising from a fingermark dating perspective. Further research is required to fully validate such models and assess their robustness and limitations in uncontrolled casework conditions.

Revealing the spatial distribution of chemical species within latent fingermarks using vibrational spectroscopy

“…Herein, we shall refer to water-soluble (hydrophilic) chemical components and water-insoluble (lipophilic) chemical components as eccrine and sebaceous material, respectively. There have been a number of investigations of the bulk chemical composition of fingermarks, [2][3][4][5][6][7] yet the spatial distribution of eccrine and sebaceous chemical components within the deposit is less well understood. Fingermark composition is often characterised by bulk measurement techniques such as GC-MS and LC-MS. [2][3][4]6,8 Although bulk methods do not reveal spatial distribution, they have provided an important insight into time-course chemical alterations that occur in fingermarks following deposition.…”

The Effect of Temperature and Exposure Time on Stability of Cholesterol and Squalene in Latent Fingermarks Deposited on PVDF Membrane

“…Conversely, at temperatures of −20, 4°C, RT, and 60°C, it is possible to develop fingermarks after 4–8 h. In addition, our results show a reduction in the cholesterol and squalene standards when exposed to 60°C for 4 and 8 h, whereas no significant difference in these compounds was detected in natural fingermarks at this temperature. We speculate that this may be due to interactions with other natural fingermark components, such as triglycerides and fatty acids . Another assumption may be due to the emulsions like nature of lipid and eccrine constituents in fingermark droplets .…”

“…Because these compounds are detected in fingermarks at a high frequency, they have been studied as potentially useful targets for latent fingermark enhancement techniques (5)(6)(7). In addition, they can persist for several days, which is important for aging studies (8)(9)(10). Previous studies measuring the degradation of cholesterol and squalene in fingermark residue have been conducted under various conditions, including time and light (11)(12)(13)(14)(15).…”

An update on MALDI mass spectrometry based technology for the analysis of fingermarks – stepping into operational deployment

“…Other authors had already published studies (and some are very recent 43 ) using different techniques such as GC-MS [44][45][46] and Fourier transform infrared microscopy (μ-FTIR) 47 , demonstrating significant changes in lipid composition over time. Though these fundamental studies are hugely important to understand how a mark may age, not knowing the reference levels of the endogenous lipids at the time of deposition (every donor is different and every donor may present a different composition at different times of the day) does not make these studies readily implementable.…”