Analysis of amino acid enantiomers from aged fingerprints

Fingerprints found at a crime scene can be key in criminal investigations. A method to accurately determine the age of the fingerprint, potentially crucial to linking the fingerprint to the crime, is not available at the moment. In this paper, we show that the use of the enantiomeric ratio of d/l-serine in fingerprints could pose as interesting target for age estimation techniques. We developed a UPLC-MS/MS method to determine the enantiomer ratios of histidine, serine, threonine, alanine, proline, methionine and valine from fingerprint residue. We found a significant change only in the relative ratio of d-serine with increasing fingerprint age after analysis of fingerprints up to 6 months old.

Fingerprints can be crucial evidence in criminal investigations. The unique ridge detail can be used to individualize a perpetrator, if the fingermark is of sufficient quality and the reference fingerprint is present in the database. It is generally accepted that a fingermark found on an object is established by contact of the donor's finger and the object. However, the time at which this contact has taken place, which can be crucial to link the perpetrator to the crime, can at present not be derived from the fingermark. Therefore, fingerprint age estimation has been a topic of interest in the past decades. The main focus to estimate the time of deposition has been on using chemical changes in the composition of fingermark residue. After deposition, the molecules that make up a fingerprint are subject to degradation, such as hydrolysis and oxidation reactions.1 Several investigations aimed at these changes to predict the age of a fingerprint. Studying fingerprint ageing using gas chromatography mass spectrometry (GC-MS), Archer et al. described the degradation of fatty acids and squalene in fingerprints after deposition on a surface. Weyermann et al., also based on GC-MS analyses, suggested a ratio between squalene and cholesterol as potential predictor for fingerprint age. In subsequent research, Koenig et al. proposed to add wax ester compounds to the equation to reduce variability in initial composition. Pleik et al. focused on the identification of degradation products of common fatty acids in fingerprints as potential tool for age determination. Van Dam et al. used fluorescence spectroscopy to determine the relative amount of fluorescent oxidation products to estimate the age of fingerprints from male donors up to three weeks old, within several days' accuracy. Alternatively, Oonk et al., using a proteomics approach, suggested several potential protein markers to estimate fingerprint age. More recently, Hinners et al., suggested the ozonolysis of triacylglycerols as a means of determining the age of a fingerprint, and showed its potential as age marker in fingerprints up to one week old.8 However, parameters often complicating accurate fingerprint age estimation are the influences of environmental factors such as temperature, humidity and light exposure.