A review on touch DNA collection, extraction, amplification, analysis and determination of phenotype

Development of a multiplex recombinase amplification assay for the rapid and concurrent detection of human DNA and sex identification

In forensic practice, it is essential to identify human DNA and determine the sex of individuals from biological samples collected at crime scenes. Currently, the common detection methods mainly focus on targeted DNA analysis based on PCR technology, which is time-consuming and relies on laboratory equipment. In recent years, recombinase polymerase amplification (RPA), as one of ubiquitous isothermal amplification technology, has gained popularity across various diagnostic fields due to its advantages of rapid processing and minimal temperature control requirements. This study has developed a multiplex RPA assay suitable for human and sex components identification. The assay has good sensitivity (as low as 25 pg) and strong tolerance to inhibitors (in the presence of 200 ng/μL humic acid, 400 ng/μL tannic acid, and 8000 ng/μL collagen). Furthermore, we combined the alkaline lysis and RPA detection to construct a rapid detection scheme, which can shorten detection time to half an hour. We also conducted a preliminary exploration of the visualization scheme for the constructed RPA assay. The above research demonstrates simultaneous and rapid detection of human and sex components, offering an accurate and sensitive detection scheme.

Enhancing trace DNA recovery from disposable face masks: insights from the COVID-19 era and beyond

Trace DNA plays a pivotal role in forensic investigations, serving as a critical tool for linking suspects to criminal activities. During the COVID-19 pandemic, disposable face masks emerged as key items of forensic interest, particularly in cases where suspects used them to conceal their identities. This study evaluates the efficiency of two trace DNA collection methodologies-cotton swabbing and tapelifting-for recovering DNA from face masks. Samples were collected from 50 masks worn by suspects in robbery cases, utilizing the Copan cotton swab (150 C) and the SceneSafe Fast™ minitape (K545). Statistical analysis revealed that minitapes (MT) significantly outperformed cotton swabs (CS), yielding higher DNA concentrations (mean MT: 0.41 ng/µL, CS: 0.17 ng/µL; p < 0.05) and recovering more complete DNA profiles, including full single (FS) and full mixed (FM) profiles (p < 0.05). These findings highlight the superior efficiency of MT, particularly for recovering trace DNA from small or fabric-like surfaces. The study underscores the importance of selecting optimal collection methods in forensic investigations, especially for modern evidence types such as face masks. Recommendations include the routine adoption of minitapes in casework involving face masks and further research into their efficacy on other mask types and under varied environmental conditions. This research offers valuable insights to refine trace DNA recovery strategies, enhancing the reliability of forensic evidence.

Thread-powered cell lysis and isotachophoresis: unlocking microbial DNA for diverse molecular applications

Central to the domain of molecular biology resides the foundational process of DNA extraction and purification, a cornerstone underpinning a myriad of pivotal applications. In this research, we introduce a DNA extraction and purification technique leveraging polypropylene (PP) threads. The process commences with robust cell lysis achieved through the vigorous agitation of interwoven PP threads. The friction between the threads facilitates cell lysis especially those microbes having tough cell wall. For purification of DNA, thread-based isotachophoresis was employed which makes the whole process swift and cost-effective. Lysed cell-laden threads were submerged in a trailing electrolyte which separated DNA from other cellular contents. The process was performed with a tailored ITP device. An electric field directs DNA, cell debris, trailing electrolyte, and leading electrolyte toward the anode. Distinct ion migration resulted in DNA concentrating on the PP thread's anode-proximal region. The SYBR green dye is used to visualize DNA as a prominent green zone under blue light. The purified DNA exhibits high purity levels of 1.82 ± 0.1 (A260/A280), making it suitable for various applications aiming at nucleic acid detection.

Application of a Modified 3D-PCSI-MS Ion Source to On-Site, Trace Evidence Processing via Integrated Vacuum Collection

Trace evidence, including hair, fibers, soil/dust, and gunshot residue (GSR), can be recovered from a crime scene to help identify or associate a suspect with illegal activities via physical, chemical, and biological testing. Vacuum collection is one technique that is employed in recovering such trace evidence but is often done so in a targeted manner, leaving other complementary, chemical-specific information unexamined. Here, we describe a modified 3D-printed cone spray ionization (3D-PCSI) source with integrated vacuum collection for on-site, forensic evidence screening, allowing the processing of targeted physical traces and nontargeted chemical species alike. The reported form factor allows sample collection, onboard extraction, filtration, and spray-based ionization in a singular vessel with minimal handling of evidence by the operator. Utilizing authentic forensic evidence types and portable MS instrumentation, this new method was characterized through systematic studies that replicate CSI applications. Reliability in the form of false positive/negative response rates was determined from a modest, user-blinded data set, and other attributes, such as collection efficacy and detection limit, were examined.

Preliminary Study: DNA Transfer and Persistence on Non-Porous Surfaces Submerged in Spring Water

Submerged items are often thought to lack evidentiary value. However, previous studies have shown the ability to recover DNA from submerged porous items for upwards of six weeks. The crevices or interweaving fibers in porous items are thought to protect DNA from being washed away. It is hypothesized that, because non-porous surfaces do not have the same traits that might aid in DNA retention, then DNA quantities and the number of donor alleles recovered would decrease over longer submersion periods. Additionally, it is hypothesized that DNA quantity and the number of alleles would be negatively affected by flow conditions. Neat saliva of known DNA quantity was applied to glass slides and exposed to stagnant and flowing spring water to observe the effects on both DNA quantity and STR detection. Results supported that DNA deposited onto glass and subsequently submerged in water experienced a decrease in DNA quantity over time, yet submersion did not have as strong of a negative effect on the detected amplification product. Additionally, an increase in DNA quantity and detected amplification product from designated blank slides (no initial DNA added) could indicate the possibility of DNA transfer.

Application of Forensic DNA Phenotyping for Prediction of Eye, Hair and Skin Colour in Highly Decomposed Bodies

In the last few years, predicting externally visible characteristics (EVCs) by adopting informative DNA molecular markers has become a method in forensic genetics that has increased its value, giving rise to an interesting field called "Forensic DNA Phenotyping" (FDP). The most meaningful forensic applications of EVCs prediction are those in which, having only a DNA sample isolated from highly decomposed remains, it is essential to reconstruct the physical appearance of a person. Through this approach, we set out to evaluate 20 skeletal remains of Italian provenance in order to associate them with as many cases of missing persons as possible. To achieve the intended goal, in this work we applied the HIrisPlex-S multiplex system through the conventional short tandem repeats (STR) method to confirm the expected identity of subjects by evaluating phenotypic features. To investigate the reliability and accuracy of the DNA-based EVCs prediction, pictures of the cases were compared as they were available to researchers. Results showed an overall prediction accuracy greater than 90% for all three phenotypic features-iris, hair, and skin colour-at a probability threshold of 0.7. The experimental analysis showed inconclusive results in only two cases; this is probably due to the characteristics of subjects who had an intermediate eye and hair colour, for which the DNA-based system needs to improve the prediction accuracy.

Touch DNA Sampling Methods: Efficacy Evaluation and Systematic Review

Collection and interpretation of "touch DNA" from crime scenes represent crucial steps during criminal investigations, with clear consequences in courtrooms. Although the main aspects of this type of evidence have been extensively studied, some controversial issues remain. For instance, there is no conclusive evidence indicating which sampling method results in the highest rate of biological material recovery. Thus, this study aimed to describe the actual considerations on touch DNA and to compare three different sampling procedures, which were "single-swab", "double-swab", and "other methods" (i.e., cutting out, adhesive tape, FTA® paper scraping), based on the experimental results published in the recent literature. The data analysis performed shows the higher efficiency of the single-swab method in DNA recovery in a wide variety of experimental settings. On the contrary, the double-swab technique and other methods do not seem to improve recovery rates. Despite the apparent discrepancy with previous research, these results underline certain limitations inherent to the sampling procedures investigated. The application of this information to forensic investigations and laboratories could improve operative standard procedures and enhance this almost fundamental investigative tool's probative value.