Assessing the thermal stability of toolmarks casting materials through optical comparison microscopy, virtual comparison microscopy and quantitative similarity scores.

Toolmarks, particularly those found on bulky, inaccessible or immovable items, can be recovered by casting. To allow for subsequent comparative examinations, the casting material, typically polysiloxanes or silicones, must be able to capture and preserve fine details within a toolmark accurately. To study the stability of such details after exposure to heat, toolmark casts were heated at either 60 °C for 2 h, or 90 °C for 1 h. These casts were subsequently compared to casts that had not been exposed to heat, using traditional optical comparison microscopy, as well as virtual comparison microscopy. Digitised toolmark signatures were also extracted from the casts and compared pairwise to obtain quantitative similarity scores based on cross-correlation, consecutive matching striae and Mann-Whitney U-statistic. Our results show that the fine surface details captured on all four commercial toolmark casting materials tested herein remained stable after exposure to heat. This study shows that the above heating protocols are viable viral inactivation methods for toolmark casts that are potentially contaminated with human coronaviruses, such as SARS-CoV-2. Our findings also apply to other scenarios, such as for casts that were left in a vehicle parked under the sun.

Forensic examination of plastic drinking straws based on their physical characteristics and manufacturing marks.

This work highlights the evidential value of examining plastic drinking straws to establish linkages between multiple sources for forensic intelligence, investigative or prosecution purposes. Plastic drinking straws are commonly encountered in drug cases, either as inhalational paraphernalia or as packaging material. However, to the best of our knowledge, systematic studies on the evidential value of straws have not previously been carried out. In this study, over 80 packets of clear and colourless straws-most of which were visually similar-were purchased from various commercial outlets in Singapore. Some physical characteristics (viz., polarizing patterns, thickness, circumference and mass per unit length) and the manufacturing marks of these straws were examined to assess their potentials for discriminating straws from different packets. Comparison of polarizing patterns yielded a discrimination of approximately 69%, while thickness, circumference, and mass per unit length measurements resulted in lower discriminations. Comparison microscopy of manufacturing marks was found to be the most discriminating among all techniques employed herein, with a discrimination of about 95%, even among straws with similar polarizing patterns.

Use of Singapore's "Standard Details of Road Elements" for distance estimation in traffic crash reconstruction: A comparison with onsite measurements and Google Earth Pro.

We report the use of the geometric design standard for road markings published in the "Standard Details of Road Elements" ('SDRE') by the Land Transport Authority ('LTA') of Singapore as a convenient and sufficiently accurate means of estimating distances between features of the roadway, particularly useful for performing speed analysis based on videos. In this study, onsite measurements (by measuring tape, total station or 3D laser scanner) from various locations in Singapore, as well as the corresponding distances based on Google Earth Pro, were compared with those estimated using the SDRE. We demonstrate herein that the SDRE estimated 85.7% of all corresponding onsite measurements to within ±5%, and can thus be relied upon for crash reconstruction. This study also evaluated the distance accuracies associated with using the geometric design standard (the SDRE) and Google Earth Pro, and determined that both methods were robust and accurate, with overall average absolute percentage errors of less than 1% and would be beneficial for obtaining measurements for crash reconstruction, especially when the site of interest is not accessible.

Snap-lock bags with red band: A study of manufacturing characteristics, thermal and chemical properties.

Drug packaging is commonly submitted to the Forensic Chemistry and Physics Laboratory of the Health Sciences Authority, Singapore, for examination. The drugs seized are often packaged in plastic bags. These bags are examined for linkages to provide law enforcement with useful associations between the traffickers and drug abusers. The plastic bags submitted may include snap-lock bags, some with a red band located above the snap-lock closure and some without. Current techniques for examination involve looking at the physical characteristics (dimensions, thickness and polarising patterns) and manufacturing marks of these bags. In cases where manufacturing marks on the main body of the bags are poor or absent, the manufacturing characteristics present on the red band can be examined. A study involving approximately 1000 bags was conducted to better understand the variations in the manufacturing characteristics of the red band. This understanding is crucial in helping to determine associations/eliminations between bags. Two instrumental techniques, namely differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were explored to evaluate the effectiveness of examining the chemical composition to discriminate the bags.

Pro-oxidant properties of AZT and other thymidine analogues in macrophages: implication of the azido moiety in oxidative stress.

Zidovudine (azidothymidine, AZT) was the first drug approved for human immunodeficiency virus (HIV) treatment. Unfortunately, AZT is known to lead to severe side effects, many of which are generally thought to result from increased reactive oxygen species (ROS) production. In this work, the pro-oxidative properties of AZT and other thymidine analogues were investigated electrochemically at microelectrodes. Macrophages pre-incubated with AZT were found to release significant amounts of reactive species, including H(2)O(2), ONOO(-), NO(*) and NO(2) (-). Interestingly, the total amounts of released species were the greatest when cells were incubated with azido-containing analogues. The pro-oxidative effect of these compounds decreased significantly when the free azide terminal group was modified by reaction with a triosmium cluster. As expected, thymidine incubation did not lead to any increase in overall ROS levels. This work implicates the azido moiety in AZT-induced oxidative stress.

Simultaneous detection of reactive oxygen and nitrogen species released by a single macrophage by triple potential-step chronoamperometry.

Macrophages produce reactive oxygen and nitrogen species (ROS/RNS) in response to immunological challenges. We have previously reported the real-time detection and quantification of released ROS/RNS by immunostimulated macrophages using constant potential amperometry, at four different potentials, with platinized carbon microelectrodes. As a methodological extension to that work, we sought to develop an electroanalytical method that would allow for the simultaneous monitoring of several ROS/RNS. Triple potential-step chronoamperometry at platinized carbon microelectrodes was found to provide satisfactory sensitivity and signal/noise ratio for this purpose. The title method was applied to the detection of endogenously produced ROS/RNS by single IFN-gamma/LPS/PMA stimulated RAW 264.7 macrophages. Significantly higher fluxes of H(2)O(2), ONOO(-), and NO* responses were detected over stimulated macrophages as compared to unactivated macrophages, consistent with the endogenous production of primary NO* and O(2)(*-) by both the inducible isoform of nitric oxide synthase (iNOS) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzymatic systems in stimulated cells. Crucially, significant temporal variations in the release of each of the aforementioned species was evidenced using this method, which would not have been achievable with the use of either constant potential amperometry or classical biochemical methods such as the Griess assay.

Real-time amperometric analysis of reactive oxygen and nitrogen species released by single immunostimulated macrophages.

Macrophages are key cells of the immune system. Immunologically activated macrophages are known to release a cocktail of reactive oxygen and nitrogen species. In this work, RAW 264.7 macrophages were activated by interferon-gamma and lipopolysaccharide, and the reactive mixture released by single cells was analyzed, in real time, by amperometry at platinized carbon microelectrodes. In comparison with untreated macrophages, significant increases in amperometric responses were observed for activated macrophages. Nitric oxide (NO*), nitrite (NO2*-), and peroxynitrite (ONOO-) were the main reactive species detected. The amounts of these reactive species were quantified, and their average fluxes released by a single, activated macrophage were evaluated. The detection of ONOO- is of particular interest, as its role and implications in various physiological conditions have been widely debated. Herein, direct evidence for the formation of ONOO- in stimulated macrophages is presented. Finally, the presence of 1400W, a selective inducible nitric oxide synthase (iNOS) inhibitor, led to an almost complete attenuation of the amperometric response of activated RAW 264.7 cells. The majority of the reactive species released by a macrophage are thus likely to be derived from NO* and superoxide (O2*-) co-produced by iNOS.