New Horizons for Estimating the Time Since Deposition of Fingermarks: Combining Label-Free Physical Visualization and Electrochemical Characterization

Abstract

The time since deposition (TSD) of latent fingermarks (LFMs) serves as "witnesses" for crime scene reconstructions. Nevertheless, existing TSD prediction approaches focused on either physical or chemical aging parameters leading to inaccurate estimation. A novel label-free protocol has been developed, where both physical ridge patterns and lipid oxide (LipOx) degradation kinetics are realized using optical microscopy and scanning electrochemical microscopy (SECM) and combined for TSD prediction. Specifically, the surface interrogation (SI)-SECM titration was utilized to monitor the LipOx degradation in LFM arrays aligned by hole array masks, through which we derived the LipOx degradation function. After establishing the relationship between several titration parameters and titrated area by experimental and numerical simulation methods, the titrated area could be reasonably estimated and subsequently used to calculate the surface coverage of LipOx. Results demonstrated that the tip transient revealed the LipOx coverage of deposited LFMs. Notably, LipOx coverage was found to increase during the first day and then decrease over time, whose degradation rate was susceptible to light. Thus, TSD candidates of an LFM could be limited to two values through the established function. Due to the nonmonotonic trend of LipOx aging, a physical parameter "the gray value ratio (GVR) of furrows to ridges" was proposed to exclude irrelevant TSD through support vector machine (SVM) classification. Ultimately, we predicted TSDs of seven LFMs with estimation errors of 2.2−26.8%. Overall, our strategy, with the outperformed capability of gleaning physical and electrochemical information on LFMs, can provide a truly label-free way of studying LFMs and hold great promise for multidimensional fingerprint information analysis.

Predicting Fingerprint Age Based on Ozonolysis Kinetics of Unsaturated Triacylglycerol Degradation

“…Most of all, as an unbiased surface MS technique, MALDI-MS can simultaneously detect other fingerprint chemicals and their images without the necessity for solvent extraction in GC–MS or LC–MS. Most chemical-based TSD methods are required to control absolute deposition amount, ,, whereas our approach is based on the relative abundance of TGs with saturated TGs as an internal standard. Finally, fingerprint lipids are expected to be more robust aging markers than amino acids, water content, or others as they are resistant to evaporation or other losses and are highly abundant in latent fingerprints. ,,, …”

“…Further, the fluorescence ratio of Tryp to fluorescent oxidation product is used to estimate the TSD of fingerprints for a few weeks period . Most recently, scanning electrochemical microscopy is used to estimate TSD by monitoring lipid oxide degradation combined with physical ridge pattern analysis . In most of these studies, however, the amount of deposited fingerprints had to be controlled, again limiting the applicability to forensic investigations …”

“…19 Most recently, scanning electrochemical microscopy is used to estimate TSD by monitoring lipid oxide degradation combined with physical ridge pattern analysis. 20 In most of these studies, however, the amount of deposited fingerprints had to be controlled, again limiting the applicability to forensic investigations. 18 Pleik et al used LC−MS to show that fingerprint triacylglycerols (TGs) undergo ozonolysis in ambient conditions.…”

Determination of the Time since Deposition of blood‐traces in a forensic context: Application of untargeted LC‐HR‐MS/MS metabolomics profiling

“…Earlier works investigated hemoglobin chemistry by ultraviolet–visible spectrometry 4,5 . At the same time, more recent approaches have used various other analytical techniques, such as atomic force and scanning microscopy, 6–8 Raman, fluorescence, reflectance spectroscopy, 9–11 and electrochemistry 12,13 …”

“…4,5 At the same time, more recent approaches have used various other analytical techniques, such as atomic force and scanning microscopy, [6][7][8] Raman, fluorescence, reflectance spectroscopy, [9][10][11] and electrochemistry. 12,13 Studies examining the aging-dependent dynamics of DNA and RNA were shown to be promising and have taken up considerable interest in recent years. [14][15][16][17][18][19][20][21][22][23] High-performance liquid chromatography coupled to mass spectrometry (HPLC-MS)-based approaches have recently been used to study TsD determination.…”