Proteomics Goes to Court: A Statistical Foundation for Forensic Toxin/Organism Identification Using Bottom-Up Proteomics.

Bottom-up proteomics is increasingly being used to characterize unknown environmental, clinical, and forensic samples. Proteomics-based bacterial identification typically proceeds by tabulating peptide "hits" (i.e., confidently identified peptides) associated with the organisms in a database; those organisms with enough hits are declared present in the sample. This approach has proven to be successful in laboratory studies; however, important research gaps remain. First, the common-practice reliance on unique peptides for identification is susceptible to a phenomenon known as signal erosion. Second, no general guidelines are available for determining how many hits are needed to make a confident identification. These gaps inhibit the transition of this approach to real-world forensic samples where conditions vary and large databases may be needed. In this work, we propose statistical criteria that overcome the problem of signal erosion and can be applied regardless of the sample quality or data analysis pipeline. These criteria are straightforward, producing a p-value on the result of an organism or toxin identification. We test the proposed criteria on 919 LC-MS/MS data sets originating from 2 toxins and 32 bacterial strains acquired using multiple data collection platforms. Results reveal a > 95% correct species-level identification rate, demonstrating the effectiveness and robustness of proteomics-based organism/toxin identification.

Human odor and forensics. Optimization of a comprehensive two-dimensional gas chromatography method based on orthogonality: How not to choose between criteria.

The use of comprehensive two-dimensional gas chromatography coupled with mass spectrometry would be a real asset for the forensic profiling of human hand odor. This paper focuses on the optimization of a comprehensive gas chromatography method using a synthetic mixture of 80 compounds representative of human hand odor composition. In order to rank the candidate column sets, instead of using a unique criterion, we used a chemometric tool called desirability which is based on Derringer functions and enables to consider several criteria simultaneously and hence to get the best compromise. Nine criteria including six orthogonality criteria were used to evaluate the quality and the efficiency of the separation. The desirability analysis lead to a straightforward ranking and an accurate overview of the results in two situations, with an objective of routine analysis and without. In both cases, the DB-1MS×DB-1701 set was found to be best suited for the separation of the considered mixture, however with different gradients.

Magnetic susceptibility and isothermal remanent magnetization in human tissues: a study case.

This study evaluated the magnetic properties, magnetic susceptibility and isothermal remanent magnetization (IRM) of tissue samples from the brain, liver, spleen, pancreas, heart and lungs, resected from human corpses, with the aim of identifying the magnetic mineral structures and understanding their possible connection to diseases, professional activity, age and gender of the individual, smoking habits and the environment. The heart was the organ with the highest values of magnetic susceptibility and the pancreas showed the lowest values. No relationship was found between magnetic susceptibility, IRM values and ages of the individuals. However the samples obtained in females showed lower values of magnetic susceptibility than those resected from males. The samples collected from the lungs of smokers have higher values of magnetic susceptibility and IRM indicating the presence of magnetic particles with an anthropic origin. Moreover, the complexity of the magnetic behaviour of these tissues may suggest a contribution of both biogenic and anthropogenic magnetic particles also due to some professional activities. In the brain a heterogeneous distribution of the magnetic susceptibility values was found, which might be related mainly to the diamagnetic behaviour of myelin-rich structures. This study suggests that although the diamagnetic and paramagnetic behaviour is common to all structures, magnetite-type structures are always present in the tissues and hematite-type structures may also contribute to the magnetic signal of the sample. IRM values are only dependent on the presence of magnetite or hematite-type magnetic structures and so this technique seems more suitable to achieve the characterization of biomagnetic structures than magnetic susceptibility.

Applications of resistive heating in gas chromatography: a review.

Gas chromatography is widely applied to separate, identify, and quantify components of samples in a timely manner. Increasing demand for analytical throughput, instrument portability, environmental sustainability, and more economical analysis necessitates the development of new gas chromatography instrumentation. The applications of resistive column heating technologies have been espoused for nearly thirty years and resistively heated gas chromatography has been commercially available for the last ten years. Despite this lengthy period of existence, resistively heated gas chromatography has not been universally adopted. This low rate of adoption may be partially ascribed to the saturation of the market with older convection oven technology, coupled with other analytical challenges such as sampling, injection, detection and data processing occupying research. This article assesses the advantages and applications of resistive heating in gas chromatography and discusses practical considerations associated with adoption of this technology.

The forensiX evidence collection tube and its impact on DNA preservation and recovery.

Biological samples are vulnerable to degradation from the time they are collected until they are analysed at the laboratory. Biological contaminants, such as bacteria, fungi, and enzymes, as well as environmental factors, such as sunlight, heat, and humidity, can increase the rate of DNA degradation. Currently, DNA samples are normally dried or frozen to limit their degradation prior to their arrival at the laboratory. In this study, the effect of the sample drying rate on DNA preservation was investigated, as well as a comparison between drying and freezing methods. The drying performances of two commercially available DNA collection tools (swab and drying tube) with different drying rates were evaluated. The swabs were used to collect human saliva, placed into the drying tubes, and stored in a controlled environment at 25°C and 60% relative humidity, or frozen at -20°C, for 2 weeks. Swabs that were stored in fast sample drying tubes yielded 95% recoverable DNA, whereas swabs stored in tubes with slower sample drying rates yielded only 12% recoverable DNA; saliva stored in a microtube at -20°C was used as a control. Thus, DNA sampling tools that offer rapid drying can significantly improve the preservation of DNA collected on a swab, increasing the quantity of DNA available for subsequent analysis.

Analysis of synthetic canine training aids by comprehensive two-dimensional gas chromatography-time of flight mass spectrometry.

Cadaver dogs are trained on a variety of materials, including artificial or pseudo scents. The chemical components of commercially available pseudo scents are not known, so their accuracy as a decomposition odour mimic and their effectiveness as a canine training aid have not been evaluated. Two pseudo scents that are commercially available and used for training cadaver dogs were analysed using comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-TOFMS). The two formulations were determined to be simplistic in their composition, compared to real cadaveric volatile organic compound (VOC) mixtures, with only a few major components. The enhanced GC×GC-TOFMS peak capacity was nevertheless useful to discriminate less intense peaks from large overloaded peaks. The availability of both dimension retention times combined with the peak finding and deconvolution algorithm, enabled the chemical characterization of the two formulations. Additionally, high resolution (HR) TOFMS was used to extract molecular formulae and confirm identities of analytes. The seven compounds identified by this work have not been reported previously as volatile products of decomposition, indicating that these pseudo scents are not to be considered as an accurate representation of cadaveric decomposition odour. Further research on the olfaction of scent detection canines and the chemical composition of their target odourants needs to be conducted to develop improved canine training aids.

Identifying transfer mechanisms and sources of decabromodiphenyl ether (BDE 209) in indoor environments using environmental forensic microscopy.

Although the presence of polybrominated diphenyl ethers (PBDEs) in house dust has been linked to consumer products, the mechanism of transfer remains poorly understood. We conjecture that volatilized PBDEs will be associated with dust particles containing organic matter and will be homogeneously distributed in house dust. In contrast, PBDEs arising from weathering or abrasion of polymers should remain bound to particles of the original polymer matrix and will be heterogeneously distributed within the dust. We used scanning electron microscopy and othertools of environmental forensic microscopy to investigate PBDEs in dust, examining U.S. and U.K. dust samples with extremely high levels of BDE 209 (260-2600 microg/g), a nonvolatile compound at room temperature. We found that the bromine in these samples was concentrated in widely scattered, highly contaminated particles. In the house dust samples from Boston (U.S.), bromine was associated with a polymer/organic matrix. These results suggest that the BDE 209 was transferred to dust via physical processes such as abrasion or weathering. In conjunction with more traditional tools of environmental chemistry, such as gas chromatography/mass spectrometry (GC/MS), environmental forensic microscopy provides novel insights into the origins of BDE 209 in dust and their mechanisms of transfer from products.

Forensic analysis of poly(ethylene terephthalate) fibers by infrared spectroscopy.

Poly(ethylene terephthalate) (PET) is one of the most commonly employed polymers in the textile industry. Its relevance as a source of evidence in the reconstruction of criminal cases is nevertheless very limited because the properties and morphologies of fibers from different producers tend to be very similar. By integrating bands, obtained on single fibers by infrared (IR) microscopy, associated with trans and gauche conformation and to the O-H end-groups of the molecules, a method is proposed that can discriminate otherwise similar PET fibers. The absorbancies at 1370 and at 846 cm(-1) relative, respectively, to the gauche and trans conformation, were measured and ratioed. The end-group content was evaluated by ratioing the absorbancies of the signals at 3440 and at 874 cm(-1). Relative standard deviation (R. S. D.) was 1% for repetitive analyses on the same location of the same single fiber. Precision was reduced if the ratios were measured along the length of a single fiber (R. S. D. = 3%) and even further when different fibers of the same sample were examined (R. S. D. varied from 2 to 10%). This simple method can greatly enhance the evidential value of PET fibers by subclassifying them, thus helping the Court to better assess their significance.