| 1. |
- Hedman, Johannes, et al.
(författare)
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Enhanced forensic DNA recovery with appropriate swabs and optimized swabbing technique
- 2021
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Ingår i: Forensic Science International: Genetics. - : Elsevier BV. - 1872-4973 .- 1878-0326. ; 53
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Tidskriftsartikel (refereegranskat)abstract
- Efficient sampling with swabs is crucial for optimal forensic DNA analysis. The DNA recovery is determined by the skill of the practitioner and the compatibility between the applied swab and the surface. Here we investigate the impact of swabbing technique and swab type on the DNA yield. Thirteen different swabs from four categories (cotton, flocked nylon, small foam and large foam) provided equal DNA yields for smooth/non-absorbing surfaces. Large foam swabs gave higher DNA recovery for an absorbing wood surface. Factorial design of experiments and ANOVA was applied to study swabbing techniques for cotton swabs. Two key factors for efficient sampling were found to be 1) holding the swab with an approximate 60° angle against the surface and 2) to rotate the swab during sampling. For absorbing wood, it was beneficial to wet the swab heavily. The results of the factorial experiments were used to develop swabbing protocols for different surfaces. When ten experienced practitioners sampled according to these protocols, the DNA yield was increased for ridged plastic (around 1.25 times more DNA) and absorbing wood (2.2–6.2 times more DNA). For window glass, representing a smooth/non-absorbing surface, sampling according to the protocol gave DNA yields equivalent to applying individual sampling techniques. The protocol lowered person-to-person variation for ridged plastic. In conclusion, we have developed instructive protocols for cotton swab sampling on three types of surfaces: smooth/non-absorbing, ridged/non-absorbing and smooth/absorbing. We believe that such swabbing protocols will streamline and simplify the training of new practitioners and improve sampling efficiency for invisible DNA residues in casework.
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| 2. |
- Hedman, Johannes, et al.
(författare)
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The double-swab technique versus single swabs for human DNA recovery from various surfaces
- 2020
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Ingår i: Forensic Science International: Genetics. - : Elsevier BV. - 1872-4973 .- 1878-0326. ; 46
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Tidskriftsartikel (refereegranskat)abstract
- Most crime scene DNA evidence is retrieved using cotton swabs. Since the late 90’s, the double-swab technique has been favoured by many practitioners throughout the world. However, the superiority of double-swabbing over applying single wet swabs has not been broadly verified. Here we set out to evaluate the need for the second dry swab for various surfaces, aiming at mimicking the range of surfaces encountered at crime scenes: flat and ridged, absorbing and non-absorbing. For the tested non-absorbing surfaces, i.e., window glass, steel, brass, synthetic leather and ridged plastic, the first wet swabs gave at least 16 times higher DNA yields compared to the second dry swabs. In addition, second wet swabs gave more DNA than second dry ones, opposing the common notion that the purpose of the second swab is to absorb excess liquid. When ten experienced staff members sampled saliva stains on a window glass surface the variation between persons was considerable, with mean DNA yields for the first wet swabs ranging from 0.045 ± 0.022 to 0.13 ± 0.024 ng/μL. The first wet swabs gave 4–162 times more DNA than the second dry swabs, with higher DNA amounts on second swabs coinciding with lower amounts for first swabs. We show that for non-absorbing surfaces, the first wet swab takes up most of the cells in dried stains, making it less valuable to apply a second dry swab. The differences in DNA recovery between first and second swabs were notable also for absorbing surfaces. Double-swabbing may be preferable for some complex surfaces, but focusing on efficient sampling technique with single wet swabs is likely a better general approach.
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| 3. |
- Jansson, Linda, et al.
(författare)
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Factors affecting DNA recovery from cartridge cases
- 2020
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Ingår i: Forensic Science International: Genetics. - : Elsevier BV. - 1872-4973 .- 1878-0326. ; 48
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Tidskriftsartikel (refereegranskat)abstract
- Cartridge cases are often the sole items left behind after a shooting incident and DNA traces from these can identify persons connected to the shooting. However, the chance of retrieving usable DNA profiles from cartridge cases is limited, due to the low amounts of deposited DNA and subsequent DNA loss associated with the firing process. In the current study, we set out to increase the DNA recovery from cartridge cases and cartridges by evaluating different swab types and detergents used for trace collection. A protocol applying nylon-flocked swabs instead of cotton swabs was implemented in casework at the Swedish National Forensic Centre (NFC), increasing DNA yield. The number of samples providing a DNA concentration ≥ 0.001 ng/μL (the in-house cut-off for processing low-template samples) increased from 11.1 to 28.6 % for cartridge cases and from 16.0 to 43.3 % for cartridges. There was also a substantial increase in mixed STR profiles, too complex to use for comparisons. Thus, it was not possible to take the full advantage of the elevated DNA yield provided by nylon-flocked swabs. The number of usable STR profiles increased from 5.0 to 8.0 % for cartridge cases and remained unchanged for cartridges. Controlled studies were performed to assess the impact on the DNA recovery from different persons handling the ammunition, different material and size of the cartridge cases, and the type of firearm used. These studies reflected an ideal situation, where all cartridges were extensively handled and loaded without gloves, thus providing a higher expected DNA yield compared to most casework samples. The total peak height differed by up to a factor of ∼50 when 20 different persons handled cartridges prior to shooting. By evaluating eleven combinations of different firearms and ammunition, it was found that the casing material and type of firearm also have a substantial impact on DNA yield.
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| 4. |
- Jansson, Linda, et al.
(författare)
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Impact of swab material on microbial surface sampling
- 2020
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 0167-7012. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- Efficient microbial sampling from surfaces for subsequent detection and quantification is crucial in fields such as food safety and hygiene monitoring. Cotton swabs are traditionally used for sample collection, but today there are numerous swabs of alternative material and different sizes available. Recovery efficiencies of swabs for different applications have been compared in several studies. However, the results are often contradictory. We have compared 15 different swabs made of cotton (n = 5), flocked nylon (n = 3) and foam (n = 7), for sampling of Listeria monocytogenes and mengovirus on small (4 cm2) and large (100 cm2) areas of window glass, ridged plastic and absorbing wood. Molecular quantification methods (qPCR and RT-qPCR) were applied, and all sampling and sample processing were standardized. Specific swabs gave higher DNA/RNA yields than others, depending on both the surface characteristics and the collected target. The highest DNA yields were achieved by applying Selefa or Puritan cotton swabs for Listeria sampling on 4 cm2 areas of window glass and ridged plastic. Certain foam swabs (Critical swab with medium head and Macrofoam) gave the highest yields when sampling Listeria on 4 cm2 areas of wood and on 100 cm2 areas of ridged plastic and wood. Most foam swabs, and especially Sigma Virocult, were advantageous for virus sampling, regardless of surface. Nylon-flocked swabs showed poor recovery regardless of surface characteristics. The recovery varied substantially between swabs made of the same material, suggesting that a single swab may not be representative for a certain swab material.
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