Persistence of touch DNA on commonly encountered substrates in different storage conditions

Saliva-derived secondary DNA transfer on fabric: The impact of varying conditions

This study explored secondary DNA transfer involving saliva, a body fluid often encountered in forensic investigations. Various factors were examined to investigate their potential impact on the transfer of DNA from saliva stains deposited onto common types of fabric (cotton, nylon, and towel). We examined varying types of saliva moisture (wet, dry, and rehydrated) and different types of contact (controlled pressure and active/friction pressure) to quantitatively evaluate how such variables could impact transfer and possible conclusions surrounding saliva-derived DNA deposits. The transfer of DNA was generally least pronounced with more absorbent primary fabrics (cotton and towel materials) while a less absorbent primary fabric (nylon) exhibited a greater propensity for DNA transfer. There were significantly higher amounts of transferred DNA (p < 0.05) observed in wet saliva samples compared to dry and rehydrated saliva samples. Further, the use of active pressure (friction) appeared to result in more DNA transfer overall as compared to controlled pressure contact. Experiments conducted with wet saliva and active pressure (friction) demonstrated the highest likelihood of transfer, with the primary nylon and secondary towel fabric combination demonstrating the greatest average transfer percentage of 94.74 %. The variables explored in this study presented multiple combinations wherein a sufficient amount of DNA (≥ 240 pg total) was transferred to the secondary fabric, making it potentially suitable for STR-PCR amplification in our laboratory. The findings from this study indicate that the type of primary fabric receiving the saliva deposit, the type of saliva moisture, the type of secondary fabric and its moisture type, and the type of contact all have the potential to affect the quantity of DNA transferred and recovered. This study provides empirical data on the ease, and to what extent, DNA from saliva transfers between fabrics and aids DNA activity level evaluations. The significance of this research lies in its contribution to expanding our current understanding of DNA transfer involving saliva within forensic science and criminal investigations.

A systematic approach to the analysis of illicit drugs for DNA with an overview of the problems encountered

Due to the restricted nature of illicit drugs, it is difficult to conduct research surrounding the analysis of this drug material for any potential DNA in sufficient quantities acceptable for high numbers of replicates. Therefore, the current research available in peer reviewed journals thus far regarding analysing illicit drugs for DNA has been performed under varying experimental conditions, often using surrogate chemicals in place of illicit drugs. The data presented within this study originated from the analysis of genuine illicit drugs prepared both in controlled environments and those seized at the Australian border (and therefore from an uncontrolled environment) to determine if DNA can be obtained from this type of material. This study has been separated into three main parts (total n=114 samples): firstly, methamphetamine synthesised within a controlled environment was spiked with both saliva and trace DNA to determine the yield following DNA extraction; secondly, methamphetamine also synthesised in a controlled environment but on a larger scale was tested for the amount of DNA added incidentally throughout the synthesis, including the additional steps of recrystallising, homogenising and "cutting" the drug material to simulate preparation for distribution; and thirdly, the detection of human DNA within samples of cocaine and heroin seized at the Australian border. The DNA Fast Flow Microcon Device was utilised to concentrate all replicates from the same source into one combined extract to improve the DNA profiles for the samples where no DNA spiking occurred. Full STR profiles were successfully obtained from drug samples spiked with both saliva and trace DNA. Methamphetamine was present in the final DNA extracts and caused incompatibilities with the quantification of DNA using Qubit. The yields of DNA from drugs not spiked with DNA sources were much lower, resulting in 36 % of samples yielding alleles where all others did not. These results were not unexpected given these were realistic drug samples where the history of the drug material was unknown. This is the first study to obtain DNA profiles from genuine illicit drug material in both controlled and uncontrolled environments and indicates that the analysis of illicit drugs for DNA is an avenue worth pursuing to provide information which can in turn assist with disrupting the supply of these drugs. Given that DNA profiling is carried out worldwide using essentially the same systems as described within this study, the potential for impact is on a national and international scale.

DNA typing of cyanoacrylate fumed latent fingerprints using GlobalFiler™ and ForenSeq™ Signature Prep kits

DNA typing of latent fingerprints is highly desirable to increase chances of individualization. We recovered DNA from Cyanoacrylate (CA) fumed fingerprints and used both GlobalFiler™ and ForenSeq™ DNA Signature Prep kits for DNA typing. For GlobalFiler™, samples were processed using a protocol modified for Low Template (LT)-DNA samples (half-volume reactions, 30 cycles) while for ForenSeq™ DNA Signature Prep, samples were processed using a standard protocol and fluorometer-based library quantitation. We evaluated genotyping success and quality of profiles in terms of completeness, Peak Height Ratio/Allele Coverage Ratio, presence of PCR artifacts and drop-in alleles. With GlobalFiler™, average autosomal STR (aSTR) profile completeness was 44.4% with 2-20 pg, 54.3% with 22-60 pg, and 95% with 64-250 pg DNA input. CODIS uploadable profiles were obtained in 2/10, 3/11, and 11/12 samples in these ranges. With ForenSeq™ DNA Signature Prep, average aSTR profile completeness was 19.7% with 1-20 pg and 45.2% with 22-47 pg but increased to 78.3% with 68-122 pg and 86.7% with 618-1000 pg DNA input. Uploadable profiles were obtained in 0/12, 4/11, 4/7, and 3/3 samples for these ranges. Results show very high sensitivity using both kits. Half-volume reactions and 30 cycles had minimal negative effect on Globalfiler™ profile quality, providing support for wider use after validation experiments to routinely improve results from LT samples. A standard protocol for the ForenSeq™ DNA Signature Prep kit was also highly successful with LT DNA obtained from CA-fumed fingerprints with additional information from isometric STR alleles and other markers.

Detection of invisible biological traces in relation to the physicochemical properties of substrates surfaces in forensic casework

Touch DNA, which can be found at crime scenes, consists of invisible biological traces deposited through a person's skin's contact with an object or another person. Many factors influence touch DNA transfer, including the "destination" substrate's surface. The latter's physicochemical characteristics (wettability, roughness, surface energy, etc.) will impact touch DNA deposition and persistence on a substrate. We selected a representative panel of substrates from objects found at crime scenes (glass, polystyrene, tiles, raw wood, etc.) to investigate the impact of these characteristics on touch DNA deposition and detection. These were shown to impact cell deposition, morphology, retention, and subsequent touch DNA genetic analysis. Interestingly, cell-derived fragments found within keratinocyte cells and fingermarks using in vitro touch DNA models could be successfully detected whichever the substrates' physicochemistry by targeting cellular proteins and carbohydrates for two months, indoors and outdoors. However, swabbing and genetic analyses of such mock traces from different substrates produced informative profiles mainly for substrates with the highest surface free energy and therefore the most hydrophilic. The substrates' intrinsic characteristics need to be considered to better understand both the transfer and persistence of biological traces, as well as their detection and collection, which require an appropriate methodology and sampling device to get informative genetic profiles.

Trace DNA and its persistence on various surfaces: A long term study investigating the influence of surface type and environmental conditions - Part one, metals

It is imperative for proper evidence triage that forensic biologists understand what kind of results to expect from certain evidence types submitted for DNA analysis. The persistence of trace DNA has been insufficiently investigated and there is little data available pertaining to the persistence of DNA in different environmental conditions and on different materials. The goal of this study is to increase the available data on this topic which would, in turn, help forensic biologists manage expectations when submitting specific evidence types for DNA testing. The work presented herein is a large-scale persistence project aimed to identify trends in the persistence of trace DNA and indicate how different environmental storage conditions and target surface characteristics influence the persistence of cellular and cell free DNA (cfDNA) over time. To eliminate variation within the experiment we used a proxy DNA deposit consisting of a synthetic fingerprint solution, cellular DNA, and/or cfDNA. Samples were collected and analysed from 7 metals over the course of 1 year (27 time points) under 3 different environmental storage conditions. The results of this experiment show that metal type greatly influences DNA persistence. For instance, copper exhibited an expected poor DNA persistence (up to 4 h) which a purification step did not help increase the DNA yield. Alternatively, DNA can persist for up to a year on lead at levels potentially high enough to allow for forensic DNA testing. Additionally, this study showed that the sample storage environment had no impact on DNA persistence in most cases. When considering DNA type, cfDNA was shown to persist for longer than cellular DNA and persistence as a whole appears to be better when DNA is deposited as mixtures over when deposited alone. Unsurprisingly, it can be expected that DNA recovery rates from trace deposits will decrease over time. However, DNA decay is highly dependent on the metal surface and extremely variable at short time points but slightly less variable as time since deposition increases. This data is intended to add to our understanding of DNA persistence and the factors which affect it.

Nucleic Acids Persistence-Benefits and Limitations in Forensic Genetics

The analysis of genetic material may be the only way to identify an unknown person or solve a criminal case. Often, the conditions in which the genetic material was found determine the choice of the analytical method. Hence, it is extremely important to understand the influence of various factors, both external and internal, on genetic material. The review presents information on DNA and RNA persistence, depending on the chemical and physical factors affecting the genetic material integrity. One of the factors taken into account is the time elapsing to genetic material recovery. Temperature can both preserve the genetic material or lead to its rapid degradation. Radiation, aquatic environments, and various types of chemical and physical factors also affect the genetic material quality. The substances used during the forensic process, i.e., for biological trace visualization or maceration, are also discussed. Proper analysis of genetic material degradation can help determine the post-mortem interval (PMI) or time since deposition (TsD), which may play a key role in criminal cases.