Fingermarks are traditionally used for individualisation purposes in a criminal investigation and as evidence in the courts. In the past few decades we have seen a wide variety of novel visualisation methods being explored. Moreover, there has been an enormous increase in the technological possibilities for the chemical analysis and imaging of fingermarks. These developments have a profound implication for criminal investigations. In this chapter the highlights of the challenges in detection of fingermarks will be discussed.

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.

Escherichia coli ZraP (zinc resistance associated protein) is the major Zn containing soluble protein under Zn stress conditions. ZraP is the accessory protein of a bacterial two-component, Zn²⁺ sensitive signal transduction system ZraSR. ZraP has also been reported to act as a Zn²⁺ dependent molecular chaperone. An explanation why ZraP is the major Zn protein under the stress condition of Zn²⁺ overload (0.2 mM) has remained elusive. We have recombinantly produced E. coli ZraP and measured Zn²⁺ and Cu²⁺ affinity in-vitro using Isothermal Titration Calorimetry. ZraP has a significantly higher affinity for Cu²⁺ than for Zn²⁺. Mutation of the conserved Cys¹⁰² to Ala or Ser resulted in a change of the oligomeric state of the protein. Mutation of the conserved His¹⁰⁷ to Ala did not affect the zinc binding affinity or the oligomeric state of the protein. Deletion of the ZraP coding gene from the E. coli genome resulted in a phenotype with tolerance to very high zinc concentrations (up to 2.5 mM) that were lethal to wild type E. coli. These results exclude a direct role for ZraP in Zn²⁺ tolerance in E. coli.

Fingerprints are widely used in forensic science for individualization purposes. However, not every fingermark found at a crime scene is suitable for comparison, for instance due to distortion of ridge detail, or when the reference fingerprint is not in the database. To still retrieve information from these fingermarks, several studies have been initiated into the chemical composition of fingermarks, which is believed to be influenced by several donor traits. Yet, it is still unclear what donor information can be retrieved from the composition of one's fingerprint, mainly because of limited sample sizes and the focus on analytical method development. It this paper, we analyzed the chemical composition of 1852 fingerprints, donated by 463 donors during the Dutch music festival Lowlands in 2016. In a targeted approach we compared amino acid and lipid profiles obtained from different types of fingerprints. We found a large inter-variability in both amino acid and lipid content, and significant differences in L-(iso)leucine, L-phenylalanine and palmitoleic acid levels between male and female donors. In an untargeted approach we used full-scan MS data to generate classification models to predict gender (77.9% accuracy) and smoking habit (90.4% accuracy) of fingerprint donors. In the latter, putatively, nicotine and cotinine are used as predictors.

Traces of condom lubricants in fingerprints can be valuable information in cases of sexual assault. Ideally, not only confirmation of the presence of the condom but also determination of the type of condom brand used can be retrieved. Previous studies have shown to be able to retrieve information about the condom brand and type from fingerprints containing lubricants using various analytical techniques. However, in practice fingerprints often appear latent and need to be detected first, which is often achieved by cyanoacrylate fuming. In this study, we developed a desorption electrospray ionization mass spectrometry (DESI-MS) method which, combined with principal component analysis and linear discriminant analysis (PCA-LDA), allows for high accuracy classification of condom brands and types from fingerprints containing condom lubricant traces. The developed method is compatible with cyanoacrylate (CA) fuming. We collected and analyzed a representative dataset for the Netherlands comprising 32 different condoms. Distinctive lubricant components such as polyethylene glycol (PEG), polydimethylsiloxane (PDMS), octoxynol-9 and nonoxynol-9 were readily detected using the DESI-MS method. Based on the analysis of lubricant spots, a 99.0% classification accuracy was achieved. When analyzing lubricant containing fingerprints, an overall accuracy of 90.9% was obtained. Full chemical images could be generated from fingerprints, showing the distribution of lubricant components such as PEG and PDMS throughout the fingerprint, while still allowing for classification. The developed method shows potential for the development of DESI-MS based analyses of CA treated exogenous compounds from fingerprints for use in forensic science.

UPLC-MS is a commonly used technique to first separate complex samples and subsequently quantify molecules of interest. Herein we describe the use of UPLC-MS using an amide stationary phase to quantify non-derivatized amino acids extracted from fingerprints. As detector either a triple-quadrupole MS/MS or a TOF-MS detector was used. This method allows for a simple and fast sample preparation, which facilitates the analysis of large amounts of samples.

The amino acid profile obtained from a fingerprint may provide valuable information on its donor. Unfortunately, the collection of chemicals from the fingerprint is often destructive to the fingerprint ridge detail. Herein we detail the use of cross-linkable solutions of dextran-methacrylate to form hydrogels capable of collecting amino acids from surfaces followed by extraction and quantification with UPLC-MS. This method allows for the amino acid profile analysis of fingerprints while allowing for their increased visualization at a later stage using the standard method of cyanoacrylate fuming followed by basic-yellow dyeing.

The amino acid profile obtained from a fingerprint may provide valuable information on its donor. For forensic scientists, recovering evidence relating to the amino acid profile of a suspect can potentially be valuable for identification and exclusion purposes. Herein we detail the use of cross-linkable solutions of dextran-methacrylate to form hydrogels capable of collecting amino acids from surfaces followed by extraction and quantification with UPLC-MS. This method allows for the amino acid profile analysis of fingerprints while allowing for their increased visualisation at a later stage using the standard method of cyanoacrylation. We will demonstrate this method to also be capable of collecting DNA from fingerprints with a 20-60% yield in comparison to using a conventional cotton swab.

Background: Microbial production of nitrogen containing compounds requires a high uptake flux and assimilation of the N-source (commonly ammonium), which is generally coupled with ATP consumption and negatively influences the product yield. In the industrial workhorse Saccharomyces cerevisiae, ammonium (NH₄ ⁺) uptake is facilitated by ammonium permeases (Mep1, Mep2 and Mep3), which transport the NH₄ ⁺ ion, resulting in ATP expenditure to maintain the intracellular charge balance and pH by proton export using the plasma membrane-bound H⁺-ATPase. Results: To decrease the ATP costs for nitrogen assimilation, the Mep genes were removed, resulting in a strain unable to uptake the NH₄ ⁺ ion. Subsequent analysis revealed that growth of this Δmep strain was dependent on the extracellular NH₃ concentrations. Metabolomic analysis revealed a significantly higher intracellular NH_X concentration (3.3-fold) in the Δmep strain than in the reference strain. Further proteomic analysis revealed significant up-regulation of vacuolar proteases and genes involved in various stress responses. Conclusions: Our results suggest that the uncharged species, NH₃, is able to diffuse into the cell. The measured intracellular/extracellular NH_X ratios under aerobic nitrogen-limiting conditions were consistent with this hypothesis when NH_x compartmentalization was considered. On the other hand, proteomic analysis indicated a more pronounced N-starvation stress response in the Δmep strain than in the reference strain, which suggests that the lower biomass yield of the Δmep strain was related to higher turnover rates of biomass components.

Ammonium is the most common N source for yeast fermentations. Although its transport and assimilation mechanisms are well documented, there have been only a few attempts to measure the in vivo intracellular concentration of ammonium and assess its impact on gene expression. Using an isotope dilution mass spectrometry (IDMS)-based method, we were able to measure the intracellular ammonium concentration in N-limited aerobic chemostat cultivations using three different N sources (ammonium, urea, and glutamate) at the same growth rate (0.05 h^-1). The experimental results suggest that, at this growth rate, a similar concentration of intracellular (IC) ammonium, about 3.6 mmol NH₄ ⁺/liter_IC, is required to supply the reactions in the central N metabolism, independent of the N source. Based on the experimental results and different assumptions, the vacuolar and cytosolic ammonium concentrations were estimated. Furthermore, we identified a futile cycle caused by NH₃ leakage into the extracellular space, which can cost up to 30% of the ATP production of the cell under N-limited conditions, and a futile redox cycle between Gdh1 and Gdh2 reactions. Finally, using shotgun proteomics with protein expression determined relative to a labeled reference, differences between the various environmental conditions were identified and correlated with previously identified N compound-sensing mechanisms.