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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.

The presence of background DNA (bgDNA) can hinder the evaluation of DNA evidence at the activity level, especially when the suspect is expected to be retrieved due to their habitual occupation of the investigated environment. Based on real-life casework circumstances, this study investigates the prevalence, composition, origin, and probable transfer routes of bgDNA found on personal items in situations where their owner and person of interest (POI) share the same workspace. Baseline values of bgDNA were evaluated on the participants’ personal items. Secondary and higher degree transfer scenarios of non-self DNA deposition were also investigated. The DNA from co-workers and co-inhabiting partners can be recovered from an individual’s personal belongings. Non-self DNA present on the hands and deposited on a sterile surface can generate uninformative profiles. The accumulation of foreign DNA on surfaces over time appears to be crucial for the recovery of comparable profiles, resulting in detectable further transfer onto other surfaces. For a thorough evaluation of touch DNA traces at the activity level, it is necessary to collect information not only about DNA transfer probabilities but also about the presence of the POI as part of the ‘baseline’ bgDNA of the substrates involved.

The persistence of touch DNA deposited after realistic handling of items typically encountered in forensic investigations has been the subject of few studies. Understanding the long-term persistence of touch DNA on different substrates in varying conditions can be central to the effective triage of samples for further processing. As the time between an alleged incident and collection of evidence may vary from a few days to years after an alleged event, this study assessed three different common substrates for the persistence of touch DNA over a time span up to 9 months. These substrates included fabric, steel, and rubber, each of which were handled in a way to imitate what may happen during a criminal act. The three substrates were exposed to two different environments for up to 9 months: inside a dark cupboard with no traffic to act as a control and an outside semi-exposed environment. Ten replicates from each of the 3 substrates were tested at 5 time points to create 300 samples. All samples were processed using a standard operating workflow to provide genotype data after exposure to different environments. It was found that the fabric samples produced informative STR profiles (defined here as 12 or more alleles) up to the 9 month timepoint for either environment. The rubber and steel substrates for the inside condition produced informative STR profiles up to the 9 month timepoint, but only generated informative STR profiles for the outside condition up to 3 and 6 months, respectively. These data add to our understanding of the external factors that affect DNA persistence. •All substrates generated highly informative STR profiles for the inside condition at 9 months.•Informative profiles were generated from the fabric substrate in the outside condition at 9 months.•DNA on steel and rubber substrates was affected by the environment in the outside condition.•Rubber was the poorest performing substrate in the outside condition.

Forensic identification through DNA analysis is an accurate diagnostic tool. Deoxyribonucleic Acid (DNA) analysis is via DNA repetitive regions with less than 1 kb base size is called ‘microsatellite’ or Short Tandem Repeat (STR). At the crime scene, the perpetrator’s skin may accidentally be in contact with surrounding objects, thereby transferring trace evidence to the objects. In this study DNA was obtained using “touch DNA” from two buccal smears and two smear from watches and cellphones from volunteers who had signed the consent form. Samples were isolated using DNAzol. The quantity of DNA obtained will be measured using a UV spectrophotometer. For DNA amplification using 3 STR CODIS loci namely TH01, CSF1PO, and TPOX. The last step is visualization using acrylamide gel and silver staining. Mean levels of DNA (UVVisible Spectrophotometer) were 167.89±85.71 μg/mL for the buccal swab, 59.19±5.58 μg/mL for the watch swab, and 38.09±2.12 μg/mL for the mobile swab; the purity of the buccal swab DNA was 1.79±0.71, of the watch swab 1.69±0.76, and of the mobile swab 1.53±0.56. Visualization of PCR products on Polyacrylamide Agarose Composite Gel Electrophoresis stained with Silver and amplified using the standard primers THOI, TPOX and CSF1PO for STR Combined DNA Index System (CODIS) showed a 100% detection of amplicons. Both the buccal swab, watch swab and handphone swabs had trace amount of DNA that was sufficient to be isolated and amplified by using Polymerase Chain Reaction on the STR CODIS loci THO1, CSF1PO and TPOX.

This study evaluated the effectiveness of the amplicon RX post-PCR clean-up kit in enhancing trace DNA profile recovery from forensic casework samples amplified using the GlobalFiler PCR amplification kit. The impact of post-PCR clean-up on allele recovery and signal intensity was assessed in both trace casework samples and control samples across a range of DNA concentrations. The results showed that the amplicon RX method significantly improved allele recovery compared to the 29-cycle protocol ( p  = 8.30 × 10 −12 ) and achieved slightly better results than the 30-cycle protocol ( p  = 0.019). Additionally, the Amplicon RX method demonstrated a significant increase in signal intensity ( p  = 2.70 × 10 −4 ), reflecting improved sensitivity in detecting trace DNA profiles compared to the 30-cycle protocol. In the evaluation of control samples, the amplicon RX method consistently outperformed both the 29- and 30-cycle protocols, especially at lower DNA concentrations (D3: 0.001 ng/µL). While the performance of all methods declined at the lowest concentration (D4: 0.0001 ng/µL), the Amplicon RX method still demonstrated superior allele recovery ( p  = 0.014 compared to 29 cycles; p  = 0.011 compared to 30 cycles). Therefore, the Amplicon RX method should be widely adopted in forensic laboratories to enhance the analysis of extremely low-template and compromised samples. These findings highlight the potential of the amplicon RX post-PCR clean-up kit to improve trace DNA analysis in forensic casework. Further research is recommended to validate these results and explore its broader application in forensic DNA analysis, particularly in complex DNA mixtures and extremely low-template samples.

The trade in white rhinoceros (Ceratotherium simum) horns poses a significant threat to the survival of this species and additional investigative tools for rhino poaching cases are essentially required to address this challenge. This study explored additional techniques and challenges for recovering human touch DNA from rhino. Experiments depositing touch DNA on rhino during dehorning projects were carried out. Fifty-five human touch DNA samples were gathered from target regions on 15 rhinos (ears, head, legs, horn and back). Recovery of touch DNA using swabs with different tips and compositions as well as a tape lifting method were tested. DNA profiling was performed using the PowerPlexR ESI 16 kit (Promega). From the readable profiles (n = 35), 34 % partial and 3 % full profiles were reportable and thus it would have been possible to use these DNA profiles to link suspects to criminal activities. The study demonstrated that it is possible to obtain reportable human DNA profiles from rhinos and that the technique should be considered as an additional forensic investigative tool to be used in wildlife crimes. •Exploring the techniques for recovering human touch DNA from white rhinos to combat poaching.•Demonstrating integration of human forensic techniques into wildlife forensics.•Highlighting the role of human touch DNA in umproving wildlife crime investigations and increase convtion rates.•Obtained 34 % partial and 3 % full reportable DNA profile, potentially linking suspects to rhino poaching crimes.•Calls for enhanced sampling protocols and research on touch DNA in outdoor environments.

•Hair keratinocyte lysis protocol results in an improved DNA yield across touch deposits compared to swab lysis methods.•DNA yield increased when using a purification protocol designed for plasma cfDNA fragment.•The additional touch DNA recovered by these methods is highly degraded and thus is not effectively detected by qPCR.•Additional alleles were recovered with these methods, indicating their value even with current STR typing methods. [Display omitted] Touch deposits are a routine yet challenging sample type in forensic casework and research. Recent work investigating their contents has indicated corneocytes to be the major cellular constituent while cell-free DNA is present at significant levels. Prolonged incubation including a reducing agent such as DTT has been shown to lyse corneocytes; a plasma cfDNA recovery kit which targets shorter DNA fragments has been demonstrated to improve cfDNA recovery from hand rinses. Herein these methods are combined and tested on mock casework touch deposit swabs from communal surface areas. Both fluorescence- and qPCR-based quantification methods are used and their results compared to query DNA degradation levels. Both proposed lysis and purification methods demonstrate increased recovery of DNA detectable with fluorescence quantification and some additional alleles at short loci, indicating high levels of fragmented DNA in these samples

Trace DNA is a significant type of evidence for its ability to be collected from touched items or surfaces at crime scenes to link suspects to their crimes. In cases of violent crimes like assault, sexual offences, or even homicide, often touch DNA is collected from the victim’s skin. However, the collection of touch DNA from the victim’s skin can be complex because of the mixture of DNA present, as there is likely to be a small quantity of the offender’s DNA compared to the victim’s DNA. Validating different collection methods or techniques can improve touch DNA sampling; therefore, this study investigated three collection techniques involving cotton and nylon swabs to test their efficiency for the collection of touch DNA from the human neck. There was a significant difference between the three recovery techniques used to recover touch DNA with a cotton swab (CS) (p < 0.05) and nylon swab (NS) (p < 0.05), with more alleles observed when the neck skin was moistened with 100 μL of distilled water using a spray bottle before collection with both swabs.

Illicit drugs are often made in less-than-sterile environments and can be stored in ways which can be detrimental to any DNA present, such as whether they are exposed to UV radiation. Previously, analysis of how exposure to UV impacted DNA for forensic applications has been in controlled laboratory conditions isolating a single component of UV radiation and often on DNA-rich samples such as bloodstains or saliva. To evaluate DNA persistence in more realistic conditions, capsules, such as those used to distribute controlled substances, were manually made and then packed into ziplock bags. The persistence of DNA deposited on capsules was examined when left indoors in either, complete darkness, direct sunlight in high UV conditions (summer) or in low UV conditions (winter) for three weeks in ambient room temperature. The DNA yield, STR DNA profile quality and degradation index were all analysed to determine the impact of varied UV exposure on DNA in a semi-temperature-controlled environment. Capsule samples exposed to high UV conditions had significantly reduced DNA yields, a lower number of alleles from the capsule handler and, thus, reduced likelihood ratios compared to capsules exposed to darkness and low UV conditions. Samples exposed to either darkness or low UV had little-to-no differences in all DNA quality measures tested. Despite a decreased DNA yield and poorer quality DNA profiles, capsules left in high UV conditions for three weeks have sufficient DNA for DNA profiles with over half the genetic information present. The storage conditions of drug capsules, either before or after seizure by law enforcement, can impact the DNA persistence in as little as three weeks, which is problematic for often already low concentrations of DNA in trace samples. •Increased UV exposure reduces DNA yield and DNA profile quality.•No difference in detected DNA between low and no UV conditions after three weeks.•After three weeks exposure to high UV, sufficient DNA for partial profiles remained.

DNA is used as confirmatory evidence in criminal investigations for a long time. With advancements in DNA collection and analysis, investigators can analyse samples collected at nanogram levels. For decades now, touch DNA has been used for comparison and individualization as it has a greater probability of being present at a crime scene. With the advancements in sciences, today there are methods available for the determination of phenotype for DNA sequences through analysis of Single Nucleotide Polymorphisms (SNPs). A freely available and forensically validated web software is HIrisPlex-S developed by the Erasmus Medical Centre, Netherlands in collaboration with the Walsh Laboratory of Indiana-University-Purdue-University-Indianapolis (IUPUI), USA. It can expand the horizons in forensic science enabling investigators to get an idea of the phenotype of a suspected perpetrator and thereby reduce the suspect list to a great extent. There are numerous methods enlisted for the collection and processing of touch DNA. The review paper attempts to compile the various methods adopted in touch DNA collection and analysis as well as the related literature on phenotyping using the HIrisPlex-S Software. •Touch DNA in Forensic Investigations.•Methods of Touch DNA collection and Analysis•Determination of Phenotype.•Forensically Validated Web Software - HIrisPlex-S.