Tandem detection of organic and inorganic gunshot residues using LC-MS and SEM-EDS.

Gunshot residue (GSR) is a valuable form of forensic trace evidence in the investigation of firearms crime. The current gold-standard approach does not include the analysis of organic components of the residues, which may be a deficiency, particularly in cases where there is little to no inorganic gunshot residue (IGSR) present or its attribution to a firearm source is ambiguous. A solvent extraction method was used for the extraction of organic GSR (OGSR) from the most common sampling device used to collect IGSR (i.e., SEM stubs with double-sided carbon adhesive tape). It was found that extraction did not significantly disturb inorganic GSR present on stubs, which raises the possibility that a valuable, comprehensive tandem analysis of both organic and inorganic GSR may be implemented using a single and commonly used residue collection device. The organic extract was analysed using Ultra High Performance Liquid Chromatography coupled to an Ion Trap Mass Spectrometer using Electrospray Ionisation (UHPLC-ESI-MS/MS), with preliminary results indicating that organic components can be extracted and detected at levels appropriate to casework GSR analysis. Testing of traces collected from the hands of recent shooters showed detection of stabiliser compounds typical of OGSR, which were confirmed to be present in the test ammunition's propellant. Total analysis time is approximately 30min per specimen, including preparation, instrumental analysis and data review. As the first step in the examination of GSR stubs in relation to a shooting case, extraction of organics and analysing them for the presence of OGSR may bring two operational benefits. First, that approach may be a useful way to determine which stubs warrant priority examination for IGSR, and second, it offers the possibility of providing relatively rapid case information to investigators.

An assessment of tape-lifts.

Tape-lifting is a non-destructive alternative to swabbing for collection of biological materials deposited on surfaces, especially on porous substrates. While there have been a number of studies looking at the efficiency of tapes in terms of recovery and their effect on downstream processes, none has been able to visually monitor cellular material collection. We report on a comparative study of a range of tapes regarding their collection efficiency of cellular material visualised using fluorescence microscopy, their background fluorescence after staining with DD diluted with three different solvent types and inhibition of subsequent PCR using direct PCR. Three of the fourteen tapes were selected for further testing. These were brown packing tape (Packmate™), clear tape (Sellotape®), and DNA-free tape (Lovell Surgical Solutions). These did not inhibit direct STR amplification; the other eleven tapes exhibited either high background fluorescence and/or inhibition of subsequent PCR. The effectiveness of the three tapes for the collection of cellular material was tested after tape-lifting a fingermark once, twice and ten times. The amount of cellular material within fingermarks stained with Diamond™ dye (DD) was recorded using fluorescence microscopy before and after tape-liftings. The DNA-free tape (Lovell) used in many forensic laboratories gave poor recovery compared to the other two tapes. After a tape-lift, an average of 30 % of cellular material was recovered by using DNA-free tape (Lovell), contrasting with an average recovery of 59.5 % for the clear tape (Sellotape®) and 88.8 % for the brown packing tape (Packmate™). The results presented show that standard crime scene sampling tape does collect DNA but is less effective than shop-bought tapes. Full DNA profiles can be generated from all of touched fabric samples that were collected DNA using the three tapes, triaged by DD staining and amplified by direct PCR approach.

Drosophila melanogaster odorant receptors as volatile compound detectors in forensic science: a proof-of-concept study.

The ability to detect and identify substances based on the volatile compounds (odors) they emit is relied upon heavily for numerous investigative purposes. Animals have an innate olfactory sensitivity and selectivity that out-performs current instrumentation. This has led to immense interest in their employment as chemical sensors for a range of applications, including forensic science, both as whole organisms and as sensing elements in biosensors. Using electrophysiological and calcium imaging assays, this research examined the response of Drosophila melanogaster olfactory receptors (ORs) to odor compounds significant in forensic science and assessed their potential utility as volatile compound sensors. This investigation illustrated the different sensitivities, selectivities, and sensing features of individual ORs and demonstrated that their employment for detection purposes is feasible. While further research expanding on this study will be required to demonstrate the performance characteristics that an OR-based detection system will ultimately possess, this research provides an encouraging first step towards the goal of utilizing isolated biological ORs as volatile compound sensors in forensic science.

A complementary forensic 'proteo-genomic' approach for the direct identification of biological fluid traces under fingernails.

Violent contact between individuals during a crime can result in body fluids becoming trapped under the fingernails of the individuals involved. The traces under fingernails represent valuable forensic evidence because DNA profiling can indicate from whom the trace originated and proteomic methods can be used to determine the type of fluid in the trace, thus providing evidence as to the circumstances surrounding the crime. Here, we present an initial study of an analytical strategy that involves two complementary techniques, direct PCR DNA profiling and direct mass spectrometry-based protein biomarker detection, for the comprehensive examination of traces of biological fluids gathered from underneath fingernails. With regard to protein biomarker detection, direct MALDI-ToF MS/MS is very sensitive, allowing results to be obtained from biological material present on only a few fibres plucked from a microswab used to collect the traces. Human cornulin, a protein biomarker for vaginal fluid, could be detected up to 5 h after it had been deposited under fingernails whereas haemoglobin, a biomarker for blood, is somewhat more persistent under fingernails and could be detected up to 18 h post-deposition. Bottom-up tandem mass spectrometry techniques were used to provide a high level of confidence in assigning the identity of protein biomarkers. nLC-ESI-qToF MS/MS offered higher levels of confidence and the ability to detect traces that had been present under fingernails for longer periods of time, but this performance came with the cost of longer analysis time and a more laborious sampling approach. Graphical abstract ᅟ.

A mass spectrometry-based forensic toolbox for imaging and detecting biological fluid evidence in finger marks and fingernail scrapings.

During a crime, biological material such as blood or vaginal fluid may become smeared on the fingers of the victim or suspect or trapped under their fingernails. The type of trapped fluid is extremely valuable forensic information. Furthermore, if either person touches an object at the crime scene with their 'contaminated' finger then a 'contaminated' finger mark may be deposited. Such marks have great value as they could identify not only who deposited the mark but also who they touched and which part of the body they touched. Here, we describe preliminary work towards a 'toolbox' of techniques based on mass spectrometry (MS) for the identification of biological fluid traces under fingernails or the imaging of them in finger marks. Liquid chromatography-multidimensional MS was effective for the detection of protein biomarkers characteristic of vaginal fluid and blood trapped under fingernails, even after hands had been washed. In regard to examination of finger marks for the presence of biological fluids, the most practical implementation of any technique is to integrate it with, but after, routine crime scene finger mark enhancement has been applied. Here, we demonstrate the usage of matrix-assisted laser desorption ionization-time of flight-MS for the detection and mapping of proteins and peptides from body fluids in finger marks, including marks enhanced using aluminium-containing magnetic powder and then 'lifted' with adhesive tape. Hitherto, only small molecules have been detected in enhanced, lifted marks. In a novel development, aluminium in the enhancement powder assisted ionization of small molecules in finger marks to the extent that conventional matrix was not required for MS.

Soil examination for a forensic trace evidence laboratory - Part 2: Elemental analysis.

Laser-induced breakdown spectroscopy (LIBS), X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) are compared in terms of their discrimination power when applied to Australian soil specimens. SEM/EDX and XRF are frequently used in forensic laboratories for the elemental analysis of paint and glass, and for miscellaneous examinations. LIBS is an emerging technique for forensic applications, with a number of researchers promoting its use for the elemental profiling of glass fragments. In this study, 29 soil specimens were analysed, with 12 specimens coming from the Canberra area and the remaining 17 specimens from other sites around Australia. As very good discrimination results were obtained for each of the analytical methods, any of these elemental analysis techniques, available in a trace evidence laboratory, could be used as part of a wider examination protocol to differentiate soil specimens.

Pulsed quantum cascade laser based hypertemporal real-time headspace measurements.

Optical cavity enhancement is a highly desirable process to make sensitive direct-absorption spectroscopic measurements of unknown substances, such as explosives, illicit material, or other species of interest. This paper reports advancements in the development of real-time cavity ringdown spectroscopy over a wide-bandwidth, with the aim to make headspace measurements of molecules at trace levels. We report results of two pulsed quantum cascade systems operating between (1200 to 1320)cm(-1) and (1316 to 1613)cm(-1) that measure the headspace of nitromethane, acetonitrile, acetone, and nitroglycerin, where the spectra are obtained in less than four seconds and contain at least 150,000 spectral wavelength datapoints.

Applications of synchrotron radiation in forensic trace evidence analysis.

Synchrotron radiation sources have proven to be highly beneficial in many fields of research for the characterization of materials. However, only a very limited proportion of studies have been conducted by the forensic science community. This is an area in which the analytical benefits provided by synchrotron sources could prove to be very important. This review summarises the applications found for synchrotron radiation in a forensic trace evidence context as well as other areas of research that strive for similar analytical scrutiny and/or are applied to similar sample materials. The benefits of synchrotron radiation are discussed in relation to common infrared, X-ray fluorescence, tomographic and briefly, X-ray diffraction and scattering techniques. In addition, X-ray absorption fine structure analysis (incorporating XANES and EXAFS) is highlighted as an area in which significant contributions into the characterization of materials can be obtained. The implications of increased spatial resolution on microheterogeneity are also considered and discussed.