Touch DNA collection - Performance of four different swabs.

A collaborative study conducted by three police forensic units, a DNA laboratory, and a forensic academic institute was undertaken in order to compare the performance of four different swabs in controlled and quasi-operational conditions. For this purpose, a reference swab (Prionics cardboard evidence collection kit) currently used within the police forensic units and 3 challenger swabs (COPAN 4N6FLOQSwabs™ (Genetics variety), Puritan FAB-MINI-AP and Sarstedt Forensic Swab) were used for collecting DNA traces from previously used items (referred as "touch DNA" in this article) including on 60 collars, 60 screwdrivers and 60 steering wheels obtained from volunteers. For each comparison, the surface considered was divided into two equal components; one was sampled with the reference swab and the other with one of the three challenger swabs. This lead to a total of 360 samples. Conclusions were consistent within the four operational partners. From a practical point of view, the COPAN 4N6FLOQSwabs™ (Genetics variety) was judged the most convenient to use. Furthermore, it allowed the recovery of significantly more DNA from collars (0.65 vs 0.13 ng/μL) and steering wheels (2.82 vs 1.77 ng/μL), and a similar amount of DNA from screwdrivers (0.032 vs 0.026 ng/μL) compared with the Prionics reference swab. The two other challenger swabs provided results that were not significantly different from the reference swab, except for the Puritan swab, whose performance was significantly lower for steering wheels (0.37 vs 0.58 ng/μL). As part of a conservation study, 50 μL of a blood dilution (1/4 with PBS) was deposited on a total of 105 COPAN (Genetics and Crime Scene varieties), Prionics and Sarstedt swabs. They were stored within a cupboard at room temperature. The integrity of the recovered DNA was evaluated with NGM SElect™ DNA profiles after different time-spans ranging from 1 day to 12 months by comparing the height difference of the peaks occurring at the shortest and longest loci, respectively. DNA seemed to remain stable, except when using the COPAN 4N6FLOQSwabs™ treated with an antimicrobial agent (Crime scene variety), which resulted in significant DNA degradation. Following these tests, the COPAN 4N6FLOQSwabs™ (Genetics variety), a model with a desiccant, was selected for further testing in fully operational conditions

Plant sterols: a neutron diffraction study of sitosterol and stigmasterol in soybean phosphatidylcholine membranes

International audienceNeutron scattering experiments have been performed on oriented Soybean phosphatidylcholine (SPC) bilayers, containing sitosterol or stigmasterol, two major sterols of plant plasma membranes. Sitosterol and stigmasterol were either protonated or deuterated on position C25 of the lateral chain. Incorporation of sitosterol leads to an increase of the hydrophobic thickness of SPC bilayers of 1.2 and 2 A when present, at 16 and 30 mol%, respectively. On the other hand, no change was observed when stigmasterol is present in the bilayer at its maximal solubility of 16 mol%. These results are in agreement with the fact that sitosterol is more efficient than stigmasterol to order acyl chains of SPC, as already shown with other biophysical techniques. In order to get more insight into the behavior of the lateral chains of the two sterols, the proton-deuterium contrast method was used in order to locate the (2)H25 atoms of the two sterols. For sitosterol, this atom was found close to the center of the bilayer at +/-(1.6+/-0.2 A), with a width, nu=2.5+/-0.5 A. For stigmasterol, the difference profile could be fitted in two different ways: either two possible locations are found at +/-(2.3+/-0.2 A) and +/-(10+/-0.2 A) with the same width, nu=2.5+/-0.5 A or only one broad distribution at +/-(6.1+/-0.3 A), nu=8.5+/-0.7 A. The results are discussed in terms of difference of dynamics for the lateral chain of the two sterols