Prevalence of organic gunshot residues in police vehicles

The present study investigated the organic gunshot residue (OGSR) background level of police vehicles in Switzerland. Specimens from 64 vehicles belonging to two regional police services were collected and analysed by LC-MS in positive mode. The driver’s and back seats were sampled separately to monitor potential differences between locations and to assess the risks of a suspect being contaminated by OGSR during transportation to a police station. The results showed that most of the 64 vehicles were uncontaminated (44 driver’s seats and 38 back seats respectively). Up to six of the seven targeted compounds were detected in a single sample, once on a driver’s seat and twice on back seats. The contamination frequency generally decreased as the number of compounds detected together increased. The amounts detected were in the low ng range and less than amounts generally detected just after discharge on a shooter. Our data indicated that detecting a combination of four or more compounds on a police vehicle seat appears to be a relatively rare occurrence. The background contamination observed was most probably due to secondary transfer from police officers (e.g. through recent participation in a shooting session or firearm manipulation) or from firearms stored in the vehicles. The present results might be used as a recommendation to minimize contact of a suspect with contaminated surfaces if OGSR is implemented in routine work in parallel to IGSR analysis

Bubble cell for magnetic bead trapping in capillary electrophoresis

A bubble cell capillary classically used to extend the optical path length for UV-vis detection is employed here to trap magnetic beads. With this system, a large amount of beads can be captured without inducing a strong pressure drop, as it is the case with magnetic beads trapped in a standard capillary, thereby having less effect on the experimental conditions. Using numerical simulations and microscopic visualizations, the capture of beads inside a bubble cell was investigated with two magnet configurations. Pressure-driven and electro-osmotic flow velocities were measured for different amounts of protein-A-coated beads or C18-functionalized beads (RPC-18). Solid-phase extraction of a model antibody on protein-A beads and preconcentration of fluorescein on RPC-18 beads were performed as proof of concept experiments. Figure Isovalues of the magnetic induction produced by two permanent magnets in attraction configuration with a capillary placed between the

Surveys of organic gunshot residue prevalence: comparison between civilian and police populations

This study investigated the prevalence of eight OGSR compounds in a civilian and a police population. Specimens were collected from the hands and sleeves of 122 civilians and 115 individuals working in police services using carbon stubs. Data was acquired using liquid chromatography coupled to tandem mass spectrometry. Results indicated a non-negligible prevalence in the civilian sample, with 18% of the 122 civilians sampled having one or more OGSR related compounds on their hands and 11.5% on their wrists or sleeves. For the police population, the prevalence was logically higher than for civilians, with 36.5% of the hand specimens and 33% of the wrist specimens positive for one or more compounds. A higher prevalence was expected for the second population due to the possession of service weapons regularly used during shooting exercises. These results demonstrate that the presence of one OGSR compound is not a rare occurrence, even in a civilian population. Considering the results of this research together with information on alternative sources of the targeted OGSR compounds can serve as a basis for OGSR interpretation in casework

Total serum IgE quantification by microfluidic ELISA using magnetic beads

The present work reports on the quantification of total IgE in human serum using a microanalytical device whose fluidics is driven by gravity and capillary forces only. Thanks to the eight parallel microchannels in each microchip, calibration and sample analysis are performed simultaneously. A mixture of magnetic bead/analyte/second antibody is incubated off-line and then percolated through the channels where magnetic beads are trapped, enabling the separation of the solid phase from the excess reagents. The entire assay is performed in less than 1h, and thanks to the miniaturized format, only a small volume of serum is required. Non-specific adsorption was first investigated and a blocking agent compatible with this allergy-based test was chosen. Then, the assay was optimized by determining the best magnetic bead and labelled antibody concentrations. After achievement of a calibration curve with a reference material, the protocol was applied to total IgE quantification of a patient serum sample that showed results in good accordance with those obtained by ImmunoCap® and Immunoaffinity capillary electrophoresis measurements. A detection limit of 17.5ngml−1 was achieved and good reproducibility (RSD < 10%) inter- and intra-chip was observed. Figure Off-line incubation of the patient sample with anti-IgE grafted magnetic beads and ALP-labelled anti-IgE is carried out in an Eppendorff. Detection is then performed with the GRAVI®-Cell device from DiagnoSwiss, where fluidics is driven by gravity and capillary forces onl

Magnetic track array for efficient bead capture in microchannels

Magnetism-based microsystems, as those dedicated to immunoaffinity separations or (bio)chemical reactions, take benefit of the large surface area-to-volume ratio provided by the immobilized magnetic beads, thus increasing the sensitivity of the analysis. As the sensitivity is directly linked to the efficiency of the magnetic bead capture, this paper presents a simple method to enhance the capture in a microchannel. Considering a microchannel surrounded by two rectangular permanent magnets of different length (L m = 2, 5, 10mm) placed in attraction, it is shown that the amount of trapped beads is limited by the magnetic forces mainly located at the magnet edges. To overcome this limitation, a polyethylene terephthalate (PET) microchip with an integrated magnetic track array has been prototyped by laser photo-ablation. The magnetic force is therefore distributed all along the magnet length. It results in a multi-plug bead capture, observed by microscope imaging, with a magnetic force value locally enhanced. The relative amount of beads, and so the specific binding surface for further immunoassays, presents a significant increase of 300% for the largest magnets. The influence of the track geometry and relative permeability on the magnetic force was studied by numerical simulations, for the microchip operating with 2-mm-long magnet

Analysis of major milk whey proteins by immunoaffinity capillary electrophoresis coupled with MALDI-MS

Two major milk whey proteins, β-lactoglobulin and α-lactalbumin, are among the main cowmilk allergens and can cause allergy even at a very low concentrations. Therefore, these proteins are interesting targets in food analysis, not only for food quality control but also for highlighting the presence of allergens. Herein, a sensitive analysis for β-lactoglobulin and -lactalbumin was developed using immunoaffinity capillary electrophoresis hyphenated with MALDI-MS.Magnetic beads functionalized with appropriate antibodieswere used for β-lactoglobulin and α-lactalbumin immunocapture inside the capillary. After elution from the beads, analyte focusing and separation were performed by transient isotachophoresis followed by MALDI-MS analysis performed through an automated iontophoretic fraction collection interface. A LOD in the low nanomolar range was attained for both whey proteins. The method developed was further applied to the analysis of different milk samples including fortified soy milk

A forensic investigation on the persistence of organic gunshot residues

Gunshot residues (GSR) are a potential form of forensic traces in firearm-related events. In most forensic laboratories, GSR analyses focus on the detection and characterisation of the inorganic components (IGSR), which are mainly particles containing mixtures of lead, barium and antimony originating from the primer. The increasing prevalence of heavy metal-free ammunition challenges the current protocols used for IGSR analysis. To provide complementary information to IGSR particles, the current study concentrated on the organic components (OGSR) arising from the combustion of the propellant. The study focused on four compounds well-known as being part of OGSR: ethylcentralite (EC), methylcentralite (MC), diphenylamine (DPA), N-nitrosodiphenylamine (N-nDPA). This study assessed the retention of these OGSR traces on a shooter’s hands. The overall project aim was to provide appropriate information regarding OGSR persistence, which can be suitable to be integrated into the interpretation framework of OGSR as recommended by the recent ENFSI Guideline for Evaluative Reporting in Forensic Science. The persistence was studied through several intervals ranging from immediately after discharge to four hours and two ammunition calibres were chosen: .40 S&amp;W calibre, used by the NSW Police Force; and .357 Magnum, which is frequently encountered in Australian casework. This study successfully detected the compounds of interest up to four hours after discharge. The trends displayed a large decrease in the amount detected during the first hour. A large variability was also observed due to numerous factors involved in the production, deposition and collection of OGSR

Total serum IgE quantification by microfluidic ELISA using magnetic beads

The present work reports on the quantification of total IgE in human serum using a microanalytical device whose fluidics is driven by gravity and capillary forces only. Thanks to the eight parallel microchannels in each microchip, calibration and sample analysis are performed simultaneously. A mixture of magnetic bead/analyte/second antibody is incubated off-line and then percolated through the channels where magnetic beads are trapped, enabling the separation of the solid phase from the excess reagents. The entire assay is performed in less than 1 h, and thanks to the miniaturized format, only a small volume of serum is required. Non-specific adsorption was first investigated and a blocking agent compatible with this allergy-based test was chosen. Then, the assay was optimized by determining the best magnetic bead and labelled antibody concentrations. After achievement of a calibration curve with a reference material, the protocol was applied to total IgE quantification of a patient serum sample that showed results in good accordance with those obtained by ImmunoCapA (R) and Immunoaffinity capillary electrophoresis measurements. A detection limit of 17.5 ng ml(-1) was achieved and good reproducibility (RSD < 10%) inter- and intra-chip was observed

Magnetic Core Shell Nanoparticles Trapping in a Microdevice Generating High Magnetic Gradient

Magnetic core shell nanoparticles (MCSNPs) 30 nm diameter with a magnetic weight of 10% are usually much too small to be trapped in microfluidic systems using classical external magnets. Here, a simple microchip for efficient MCSNPs trapping and release is presented. It comprises a bed of micrometric iron beads (6–8 mm diameter) packed in a microchannel against a physical restriction and presenting a low dead volume of 0.8 nL. These beads of high magnetic permeability are used to focus magnetic field lines from an external permanent magnet and generate local high magnetic gradients. The nanoparticles magnetic trap has been characterised both by numerical simulations and fluorescent MCSNPs imaging. Numerical simulations have been performed to map both the magnetic flux density and the magnetic force, and showed that MCSNPs are preferentially trapped at the iron bead magnetic poles where the magnetic force is increased by 3 orders of magnitude. The trapping efficiency was experimentally determined using fluorescent MCSNPs for different flow rates, different iron beads and permanent magnet positions. At a flow rate of 100 mL h1, the nanoparticles trapping/release can be achieved within 20 s with a preconcentration factor of 4000