The use of DNA stabilizing solution to enable room temperature storage and transportation of buccal and trace sample swabs

It is proposed that a DNA stabilizing solution (DNA Genotek Inc.) designed to preserve DNA in saliva samples at room temperature can be extrapolated to the storage of swab heads. The aim of this study was to evaluate the effectiveness of the solution for the preservation of reference swabs (buccal) and trace samples (facial swabs). To this end, the solution was used during a twin-site DNA transfer project assessing background levels of carer DNA present in children. Tubes containing 400 μl of solution were used to store and transport swab heads. At the laboratory, samples were extracted using the QIAamp DNA Mini Kit (Qiagen), quantified using the Quantifiler Duo Kit and profiled using the AmpF?STR^® SGM Plus^® PCR Amplification Kit (both Applied Biosystems). Twenty-eight PCR cycles were applied to all samples. Thirty-four cycles or a longer electrophoresis injection time was applied to trace samples where necessary. All Reference swabs produced high quantities of DNA and full DNA profiles after 28 cycles. Profile morphology indicated good quality DNA with no degradation. Of the trace samples, sufficient profiles were achieved to study the transfer of carer DNA making the solution fit for continued use in this project. DNA stabilizing solution enables the storage and transportation of swabs without freezing. This is convenient, reduces transportation costs and enables instant analysis of samples upon arrival at the laboratory. This is a useful alternative for a multi-site research project as well as a reliable storage tool for use in remote areas.     

A comparison of DNA collection and retrieval from two swab types (cotton and nylon flocked swab) when processed using three QIAGEN extraction methods

The Metropolitan Police Service currently uses cotton swabs to retrieve DNA for forensic profiling. Recently, a new nylon flocked swab type has become available from Copan (MicroRheologics, Brescia, Italy) that it is claimed, offers increased sample recovery and release yields. If true, the flocked swab may have important applications in DNA evidence retrieval. This study examines the DNA retrieval capability of cotton and nylon flocked swabs when extracted using three common extraction platforms (QIAcube, BioRobot EZ1 and manually processed QIAamp DNA investigator kit). Results indicate that both swab types are capable of recovering high percentages of DNA (>50%); however, the extraction platform selected was shown to have a significant effect upon DNA retrieval. Across all experiments, the cotton swab combined with the spin-column extractions was shown to be most effective, with the nylon swab and BioRobot EZ1 combination being the least effective. These findings illustrate the importance of extraction method selection.     

尼龙植绒拭子与棉拭子血痕DNA分型效果比较

目的探讨尼龙植绒拭子与棉拭子血痕DNA分型检验的效果。方法取抗凝全血用去离子水倍量稀释2、4、8、16、32、64、128倍,各取1μL分别滴加于尼龙植绒拭子与棉拭子头部,干燥制成血痕,应用Chelex-100提取每个浓度两种材质拭子的血痕样本DNA,采用Identifiler Plus试剂盒进行复合扩增,3500XL型遗传分析仪进行检测,对比各组DNA分型检验成功率。结果 1检验成功率:稀释16~64倍尼龙植绒拭子血痕均明显高于相同稀释倍数的棉拭子血痕(P0.001);其余浓度血痕两种材质拭子的检验成功率无明显差异;2分型图谱峰高和均衡性:不同浓度尼龙植绒拭子血痕峰高多为棉拭子血痕的2倍以上,16~64倍稀释血痕尼龙植绒拭子均衡性更好。结论尼龙植绒血痕拭子的检验效果优于棉拭子血痕,在微量血痕检验时优势更明显。     

Evaluation of the use of freezer mill to improve DNA retrieval from dried cotton swabs

This investigation evaluated the use of a freezer mill to improve retrieval of DNA from dried cotton swabs (using 100 μl saliva) compared to uncrushed swabs and whole saliva by measuring DNA yield and profile average peak height. Three treatments were tested; short, medium (as for a bone sample) and extended. The samples subjected to the freezer mill had the powder that remained on the freezer mill components collected (using a water and agitation method). All freezer mill samples returned a lower average DNA yield than either uncrushed swabs or whole saliva. The powder from the crushed swabs comprised an average of 35% of the total DNA yield, whereas the powder from the components comprised 65%. Allele drop-out was observed in samples exposed to extended treatments. Both short and medium treatments provided significantly higher peak heights than uncrushed cotton swabs with equal quantities of DNA (P < 0.05). Using a freezer mill on dried cotton swabs does not increase the DNA yield. This investigation suggests collecting powder from the freezer mill components will increase DNA yield, especially from trace samples.     

Swabs as DNA Collection Devices for Sampling Different Biological Materials from Different Substrates

Currently, there is a variety of swabs for collection of biological evidence from crime scenes, but their comparative efficiency is unknown. Here, we report the results of an investigation into the efficiency of different swab types to collect blood, saliva and touch DNA from a range of substrates. The efficiency of extracting blood and saliva from each swab type was also tested. Some swabs were significantly more effective than others for sampling biological materials from different substrates. Swabs with the highest sampling efficiency, however, often did not have the highest extraction efficiency. Observations were recorded regarding practicality of each swab in a variety of situations. Our study demonstrates that selection of sampling device impacts greatly upon successful collection and extraction of DNA. We present guidelines to assist in evaluation of swab choice.     

Contribution to the Development of Guidelines in the Analysis of Biological Evidence in Sexual Assault Investigations

This investigation intends to study materials and techniques used for biological evidence collection in sexual assault cases and is divided into two stages: in stage one, methods for biological evidence collection (the single swab (including three variants) and the “double swab technique”) were compared; in stage two, swabs’ component material was compared. The sampling was composed of 42 heterosexual couples who provided mock samples. The collection methods in which the whole swab is covered by evidence presented significantly better outcomes (p < 0.001), such as the “double swab technique.” Additionally, nylon swabs proved to present significantly better features regarding the capacity of sample elution, providing significantly higher amounts of DNA (p ≤ 0.034). This study provides guidelines for better collection of biological evidence regarding the collection method using a swab and the proper swab material to utilize.     

盗窃案件现场检材提取与DNA检测结果的统计分析

目的统计分析1574例盗窃案件中提取的2496个现场生物检材,为提高DNA在盗窃案件侦破中的应用成效提供参考。方法根据2496个生物检材的类型、现场提取方法、重点提取部位、DNA检测结果等进行统计和分析比较,总结常见类型盗窃案件现场生物检材的主要发现提取部位以及不同方法提取的现场生物检材DNA检出率。结果接触类检材已成为盗窃案件最多见的生物检材类型,但检出率仍然较低,对混合分型应进一步分析筛选以提高DNA的认定率;不同方法提取的现场生物检材在DNA检出率方面存在统计学差异,接触类生物检材以植绒拭子和原物提取的方式为首选;现场生物检材的主要发现提取部位根据盗窃案件的类型不同有所侧重。结论现场勘查人员在盗窃案件中发现和提取到有价值的生物检材是提高DNA检出认定能力的关键因素,应着力培养现场勘查人员的微量生物物证意识,提高现场勘查人员提取和处理微量生物检材的能力。     

Nitrate and Nitrite Determination in Gunshot Residue Samples by Capillary Electrophoresis in Acidic Run Buffer,

Simultaneous determination of nitrate and nitrite in gunshot residue has been conducted by capillary electrophoresis using an acidic run buffer (pH 3.5). In previously developed capillary electrophoretic methods, alkaline pH separation buffers were used where nitrite and nitrate possess similar electrophoretic mobility. In this study, the electroosmotic flow has been reversed by using low pH running buffer without any additives. As a result of reversing the electroosmotic flow, very fast analysis has been actualized, well‐defined and separated ion peaks emerge in less than 4 min. Besides, the limit of detection was improved by employing large volume sample stacking. Limit of detection values were 6.7 and 4.3 μM for nitrate and nitrite, respectively. In traditional procedure, mechanical agitation is employed for extraction, while in this work the extraction efficiency of ultrasound mixing for 30 min was found sufficient. The proposed method was successfully applied to authentic gunshot residue samples.     

Implementation of Prep-n-Go™ Buffer for DNA extraction from buccal swabs

The efficacy of two extraction methods; room temperature and heat protocols was assessed for buccal swabs using the Prep-n-Go™ Buffer. DNA was extracted from buccal swabs using both extraction methods and their effectiveness to produce good quality DNA profiles was evaluated. Heat protocol was found to yield more DNA, however room temperature protocol produced better quality DNA profiles with fewer artefacts when the samples from both extraction methods were amplified directly without any normalisation with the VeriFiler™ Express PCR Amplification Kit.