Recovery of DNA and fingerprints from touched documents

Effects of chemical & biological warfare agent decontaminants on trace survival: Impact on DNA profiling from blood and saliva

Forensic investigations following incidents involving chemical or biological agents present considerable challenges. Understanding the possibilities and limitations can aid in determining the most suitable procedures and enhancing the recovery of useful traces in these complex situations. This work complements previously published results on the effects of decontaminants on fingermarks deposited on glass. Identifying the perpetrators can be crucial, and DNA analysis remains a cornerstone in this regard. In this study, we investigated the ability to obtain usable DNA profiles from blood and saliva (pure and diluted) exposed to 16 different decontamination methods. Both DNA quantitation and DNA profiling were considered to assess the outcomes. The results revealed considerable variability but indicated that biological agents' decontaminants hindered DNA profiling post-decontamination to a greater extent than decontaminants aimed for chemical agents. Chlorine-based decontaminants also globally had a deleterious impact on DNA profiling. Powder decontaminants such as Fast-Act, CHpowder, and the liquid decontaminants GDS2000 did not affect DNA profiling.

Precision touch DNA sampling on plastic bag knots for improved profiling of packer and holder contributions

In forensic DNA analysis, evidence sampling stands as a pivotal step setting the ground for the quality of the forensic profiling. The collection of touch DNA from objects, when guidelines are scarce or absent, is usually governed by ad hoc decisions based on the available case circumstances. In our laboratory, in the context of illicit drug-related crimes, similar objects are frequently encountered, offering an opportunity for the standardization of evidence treatment. This study aims to develop an effective method for sampling touch DNA from knots on plastic bags. We examine both the exposed and hidden areas of knots, considering the latter as "protected" zones less likely to accumulate biological material during subsequent handling. The study contrasts a single sample method (whole knot surface sampling, Method 1) with dual-sample methods that separate exterior (exposed) and interior (hidden) surfaces of the knot. Notably, our study consistently reveals higher DNA yields from exterior surfaces of the knots as opposed to interior samples. Importantly, our findings demonstrate that utilizing a single sample may produce DNA profiles that are not interpretable, while employing a dual-sample approach may allow for the differentiation between the genetic contributions of the person who tied the knot, the packer, from the person who held the package, the holder. We have refined the dual-sample method to reduce holder DNA in the interior sample while maintaining it on the exterior, also allowing the packer's DNA to be detected on both surfaces. We explore four dual-sample collection methods. Method 2 involves taking the first sample from the exterior and the second from the interior of an untied knot. Method 3 visually differentiates between the original exposed and hidden surfaces for precise sampling. Method 4 employs tools to open the knot for interior sampling. Method 5 uses Diamond dye to highlight cell-free DNA on both surfaces before sampling. In conclusion, this study not only clarifies the complex dynamics of touch DNA transfer and collection on plastic bag knots, but also offers insights into standardizing evidence collection in similar cases.

Effects of solvent-based adhesive removal on the subsequent dual analysis of fingerprint and DNA

The combined approach of classical fingerprinting and DNA profiling is a powerful tool in forensic investigations of latent "touch" traces. However, little attention has been paid to the organic solvents frequently used in dactyloscopic laboratories to facilitate the separation of adhesive evidence prior to fingerprint development and downstream effects on subsequent DNA profiling. In the present study, we tested a selection of adhesive removers (n = 9) and assessed their potential impact on DNA recovery and amplification by PCR. Thereby, we identified and characterized novel PCR inhibitors. All investigated chemicals contain volatile organic compounds that evaporate under normal indoor atmospheric conditions. Exposure to certain solvents resulted in increased DNA degradation, but only if evaporation was prevented. A series of adhesive-removal experiments were conducted with prepared mock evidence (self-adhesive postage stamps affixed to paper envelope) to investigate the impact of treatment time and the location of applied traces on DNA recovery and dactyloscopy, respectively. Due to the early onset of print decomposition, we found that only a short treatment time was compatible with the development of fingerprints on the adhesive side of a stamp. Solvents also removed DNA from the adhesive surface, thus resulting in a marked shift in the substrate distribution of recovered DNA from the stamp to the envelope, but not in the reverse direction. Furthermore, we observed that treatment with conventional fingerprint reagents lead to a significant reduction in the amounts of DNA recovered from stamps, while the additional use of adhesive removers did not significantly enhance this effect.

Development of Improved DNA Collection and Extraction Methods for Handled Documents

Handwritten documents may contain probative DNA, but most crime laboratories do not process this evidence. DNA recovery should not impair other evidence processing such as latent prints or indented writing. In this study, single fingermarks on paper were sampled with flocked swabs, cutting, and dry vacuuming. In addition, two extraction methods were compared for the sample type. DNA yields were low across all methods; however, this work confirms the ability to recover DNA from paper and the usefulness of the vacuum sampling method combined with the Chelex-Tween method. Stability of touch DNA deposits were compared over an 11-month period to better understand degradation that may occur over time. No significant difference in DNA recovery was observed, suggesting DNA deposits on paper are stable over an 11-month span.

Recovery techniques for contact DNA traces

Donor DNA profiling can serve at least two purposes: 1) to enhance the evidential value of DNA deposited on garments/ items and 2) to provide valuable tactical information during crime scene investigation. In this review, different types of methods for the recovery of the contact DNA traces have been summarized. Additionally, with the available techniques, the unique characteristics and limitations thereof have been overviewed. The aim of this paper is to review the techniques of touch traces collection. Techniki odzyskiwania śladów kontaktowych DNA Profilowanie DNA dawcy może służyć co najmniej dwóm celom: 1) zwiększeniu wartości dowodowej DNA zdeponowanego na odzieży/przedmiotach oraz 2) dostarczeniu cennych informacji taktycznych podczas badania miejsca przestępstwa. W niniejszym przeglądzie podsumowano różne rodzaje metod odzyskiwania śladów kontaktowych DNA. Dodatkowo, w odniesieniu do dostępnych technik, dokonano przeglądu ich unikalnych cech i ograniczeń. Celem niniejszej pracy jest przegląd technik pozyskiwania śladów dotykowych.

Quantifying DNA loss in laboratory-created latent prints due to fingerprint processing

Fingerprints, which are associated with touch samples, typically contain a limited amount of DNA. The amount of available DNA can be further reduced when the same touch samples undergo fingerprint processing [1]. The fingerprint development process consists of high-powered lighting (inherent luminescence and UV light) and chemical compounds (ninhydrin, black powder, cyanoacrylate, and rhodamine 6 G) which could reduce DNA quality and quantity. Therefore, forensic scientists often must select one type of analysis over the other due to the destructive nature of processing. DNA and latent fingerprinting are both useful sources for identification, although both can produce partial results. A partial DNA profile may only contain a few alleles, limiting the ability to identify a potential suspect to perform comparisons. A partial fingerprint generally means that only a very small part of the fingerprint is present, which makes comparisons difficult. Because partial results are common, combining data from both fingerprinting and DNA analysis would increase the confidence of an identification of a person. Significant research has been performed to determine if a DNA profile can be obtained from latent processed fingerprints; however, there has yet to be research done in a standardized manner. In this study, we used standardized mock "fingerprints" in order to reduce fingerprint DNA variability and specifically focused on DNA quantitation after each step in the fingerprinting process. Results suggest that latent print processing techniques used on non-porous surfaces (plastic, duct-tape, metal, and rubber) do not affect DNA quantity or quality. In contrast, ninhydrin, a chemical used for processing fingerprints present on porous surfaces (wood and paper), significantly reduced DNA recovery. Together these results suggest that DNA can still be performed on latent print processed items, unless ninhydrin has been used.

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.

New Perspectives on the Importance of Cell-Free DNA Biology

Body fluids are constantly replenished with a population of genetically diverse cell-free DNA (cfDNA) fragments, representing a vast reservoir of information reflecting real-time changes in the host and metagenome. As many body fluids can be collected non-invasively in a one-off and serial fashion, this reservoir can be tapped to develop assays for the diagnosis, prognosis, and monitoring of wide-ranging pathologies, such as solid tumors, fetal genetic abnormalities, rejected organ transplants, infections, and potentially many others. The translation of cfDNA research into useful clinical tests is gaining momentum, with recent progress being driven by rapidly evolving preanalytical and analytical procedures, integrated bioinformatics, and machine learning algorithms. Yet, despite these spectacular advances, cfDNA remains a very challenging analyte due to its immense heterogeneity and fluctuation in vivo. It is increasingly recognized that high-fidelity reconstruction of the information stored in cfDNA, and in turn the development of tests that are fit for clinical roll-out, requires a much deeper understanding of both the physico-chemical features of cfDNA and the biological, physiological, lifestyle, and environmental factors that modulate it. This is a daunting task, but with significant upsides. In this review we showed how expanded knowledge on cfDNA biology and faithful reverse-engineering of cfDNA samples promises to (i) augment the sensitivity and specificity of existing cfDNA assays; (ii) expand the repertoire of disease-specific cfDNA markers, thereby leading to the development of increasingly powerful assays; (iii) reshape personal molecular medicine; and (iv) have an unprecedented impact on genetics research.

Touch DNA recovery from vehicle surfaces using different swabs

Several methods of DNA collection are used in places or objects related to crimes, the most common being the use of swabs. However, it is known that the efficacy of touch DNA recovery can be affected by collection devices and surfaces. The aim of this work was to evaluate the efficiency of three different types of swab in recovering touch DNA collected from different parts of a vehicle. The following swabs were tested: PurFlock^® swab (Puritan, USA), 4N6FLOQSwabs™ (Copan S.p.A., Italy), and cotton swab (Labor Import). The experiments were carried out in the same vehicle, using the gearshift knob, the parking brake lever, and the steering wheel as support for the collection of touch DNA. Swabs showed significant differences in the amount of DNA recovered (Hc = 53.52; p < 0.05) and in the rate of allele amplification (Hc = 24.3; p < 0.05). The results indicated a greater DNA recovery efficiency by PurFlock^® swab, followed by cotton, and then 4N6FLOQSwabs™. However, there was no significant difference among the surfaces analyzed. PurFlock^® swab was more efficient for recovering donor alleles than the others (cotton and 4N6FLOQSwabs™), especially for small DNA amounts. This swab was, therefore, suitable for collections in vehicles involved in crime. Furthermore, this study highlights the need to assess different materials and methods of collection of biological samples, considering collection, extraction, and amplification.

Who touched the document?: A new overall strategy for collection and identification of DNA from the questioned documents as a supportive evidence

The questions on which judges/prosecutors apply for expertise are mostly about by whom a document was drafted/signed. In this study, a new collective strategy was constructed including a collection method, a modified-silica-based DNA isolation method, and a novel purification method on four contact traces formed on four different paper surface during writing, using PCR with AmpFlSTR®GlobalFiler™ STR kit (after experimental comparison between three different kits) and identification using CE. This collective analysis approach is more sensitive and superior to its equivalents on questioned documents in literature because quantifiable amounts of touch DNA and profiles with high loci percentages (100% on day 1, 72.72% after 1 week) were obtained up to 1 week even after the most challenging conditions of sample forming that a forensic scientist can meet; as washing hands just before drafting and using a very low pressure in a shorter time (simulating a simple contact real conditions while drafting), using no visualizing technique that damages the document. Using the strategy, four most commonly used paper types were compared, to see in which of them DNA could be recovered better. The success of this strategy was shown on the 1-day to 10-year-old real samples from a diary and some archive documents from a law office (including the mix-DNA and different ballpoint pens). Thus, it became possible to show if a person had touched the document, in high success rates up to 1 week as a secondary evidence, when primary evidences are insufficient for the detection of document fraud offenses.

High-throughput DNA sequencing of environmentally insulted latent fingerprints after visualization with nanoscale columnar-thin-film technique

The goals of this study were to (a) ascertain human identity capabilities of DNA obtained from latent fingerprints that have been first environmentally insulted and then developed by the deposition of a columnar thin film (CTF), and (b) to determine if the CTF process and material are detrimental to single nucleotide polymorphism (SNP) analysis. Fingerprints were deposited on five different types of substrates and aged for one day, 7 days or 30 days while being environmentally insulted under one of the four conditions: 16.6 °C and 60% relative humidity (RH) (Condition A), 24.5 °C and 60% RH (Condition B), 35 °C and 67% RH (Condition C) and a cold condition (Condition D). Then CTF technique was then on 59% of these fingerprints. DNA samples from 805 fingerprints were extracted, quantified, subjected to manual library preparation using the Precision ID Identity Panel, and underwent high-throughput sequencing. The Ion S5™ platform was employed to sequence 124 SNP amplicons. SNPs were successfully sequenced from 802/805 samples. Total read depth was consistent across environmental conditions, and majority of samples had 100% profile completeness and 100% concordance. Anecdotally, libraries that were amplified with a higher cycle number had more 'Major Allele Frequency' flags compared to samples amplified with 23 cycle numbers, possibly due to stochastic effects. Neither the substrates nor the CTF process and materials inhibit downstream DNA analysis. DNA of low quality and quantity from the chosen samples can be sequenced using the Precision ID Identity Panel on the Ion S5™ platform which performed well, however, a different approach may be needed if spurious alleles are suspected.

Non-destructive DNA recovery from handwritten documents using a dry vacuum technique

Investigations of many crimes such as robberies, kidnappings, and terrorism are often associated with the recovery of a paper document which has been written by the perpetrator. Paper can provide a variety of forensic evidence such as DNA, latent fingermarks, and indented writing. The focus of this study was DNA recovery from handwritten notes through a vacuum suction device while preserving the other evidence types and the integrity of the document. Copy paper was used to create handwritten documents and sheets with deliberate fingerprints, and indentations. The homemade vacuum device consists of a glass pipette blocked with a moistened swab and attached to a vacuum source. The method collected sufficient DNA amounts for DNA typing analysis with 80% of the 11 copy paper samples tested giving probative DNA profiles with five being eligible for DNA database entry. DNA recovery was also tested on other commonly encountered paper types. DNA quantities would have been sufficient for STR typing for approximately 50% of manila envelopes and notebook paper samples, but not for magazine pages and bank deposit slips. Deliberate sebaceous and eccrine latent fingermarks placed onto copy paper and developed with magnetic fingerprint developer or 1,2 indanedione were not affected by the vacuum swabbing technique. Simulated robbery notes with indented writing and processed using an Electrostatic Detection Apparatus (ESDA) demonstrated no interference through the DNA collection. This vacuum-based collection method enables laboratories to reverse the current questioned document workflow and start with DNA collection.

The compatibility of immunolabeling with STR profiling

Immunolabeling is a technique, which has recently been introduced to enhance the quality of developed fingermarks and subsequently strengthen the evidential value. The effect of this method on subsequent DNA analysis, however, has not been explored yet. Therefore, the current pilot study aimed to determine whether STR profiling is possible after immunolabeling. Since immunolabeling involves washing steps which could reduce DNA quantities, the use of different fixatives including methanol, formaldehyde and universal molecular fixative (UMFIX) were investigated. STR profiles from the (immunolabeled) fingermarks were generated after four days and four weeks by a direct PCR method to enable comparison of relatively fresh and old fingermarks. The fingermarks were deposited on diverse forensically relevant substrates, including glass, metal and tile. STR profiles could be recovered for all tested fixatives with no significant difference in performance. However, the mean number of detected alleles was the highest when methanol was used for fixation. Furthermore, immunolabeling on aged fingermarks (4 weeks) was also possible, but the number of detected alleles showed a non-significant decrease. DNA could be recovered from deposits on all substrates, of which glass showed the highest mean number of detected alleles followed by metal and tile.

DNA profiling of saliva traces habitually deposited on various documents: a pilot study

Background

A study was conducted to determine whether the habitualness among individuals to apply saliva to their fingertips (for moistening) while shuffling through pages of a document can provide evidence in cases pertaining to handling of documents in forensic investigations. It involved 200 volunteers, 50% of which were male and 50% were female. The volunteers shuffled the pages of the three substrates (registers, books and magazines). An attempt was made to detect the transfer of saliva onto the substrate while shuffling and generation of DNA profiles from the transferred saliva. The presence of salivary stains was confirmed using iodine fuming test and starch iodine test. Afterwards, the DNA was recovered with substrate cutting method, extracted using QIAGEN® QIAmp DNA mini kit and amplified using the Power Plex® 21 System Kit.

Results

The results revealed that 83% of individuals applied saliva onto the documents and majority of females applied saliva. DNA could be successfully recovered from the stains detected on the three substrates, and complete STR profiles could be generated.

Main finding

A conclusion can be drawn out that majority of subjects under study were in habit of using saliva to turn pages, and this can be an important evidence to help criminal justice system as DNA profiles could be developed successfully from the substrates. This can be a very good evidence in respect of identifying the individual(s) who handled the document.

Detection of latent fingermarks and cells on paper

Fingermarks and DNA are valuable traces in forensic investigations potentially allowing for the identification of the source of the trace or highlighting a link between a touched object and an individual. These traces are often latent and need to be detected before recovery. While a number of validated methods exist for fingermark detection, no routine method is in place for the detection of DNA. This study investigates the use of pdimethylaminobenzaldehyde (DMAB) in conjunction with indanedione zinc (IND-Zn) for the detection of latent cellular material and fingermarks on paper. The aim of this proof-of-concept study is to determine the successfulness of this reagent (DMAB-IND) in the detection of the respective traces and observe the impact it has on the resulting DNA profile. It was found that latent fingermarks and the associated cells could be visualised following treatment with the reagent. Samples treated with DMAB-IND showed a significantly higher percentage of alleles called compared to IND-Zn-treated and untreated samples due to the targeted recovery of cells. However, the reagent appears to degrade DNA at a rapid rate, requiring the treated samples to be processed for DNA on the day of treatment.

On DNA transfer: The lack and difficulty of systematic research and how to do it better

Since DNA from touched items and surfaces ("touch DNA") can successfully and reliably be analyzed, the question as to how a particular DNA containing sample came to be from where it was recovered is of increasing forensic interest and expert witnesses in court are increasingly challenged to assess for instance whether an incriminatory DNA sample matching to a suspect could have been transferred to the crime scene in an innocent manner and to guess at the probability of such an occurrence. The latter however will frequently entail expressing a subjective probability i.e. simply making a best guess from experience. There is, to the present date, an extensive and complex body of literature on primary, secondary, tertiary and even higher order DNA transfer, its possibility, plausibility, dependency on an array of variables and factors and vast numbers of permutations thereof. However, from our point of view there is a lack of systematic data on DNA transfer with existing research widely varying in quality and relevance. Our aim was, starting from a comprehensive survey of the status quo and appreciating its increasing importance, to in the first part of our review raise consciousness towards the underestimated and insufficiently accounted for complexity of DNA transfer and thus appendant research of forensic scientists serving as expert witnesses in court but also acting in the role of a journal referee to point them to areas of criticism when reviewing a manuscript on DNA transfer. In the second part, we present propositions how to systematize and integrate future research efforts concerning DNA transfer. Also, we present a searchable database providing an extensive overview of the current state of knowledge on DNA transfer, intended to facilitate the identification of relevant studies adding knowledge to a specific question and thus help forensic experts to base their opinion on a broader, more complete and more reproducible selection of studies.

Impact of one-step luminescent cyanoacrylate treatment on subsequent DNA analysis

Fingermarks can be exploited for both their ridge detail and touch DNA. One-step luminescent cyanoacrylate (CA) fuming techniques used for fingermark enhancement, such as PolyCyano UV (Foster+Freeman Ltd) and Lumicyano™ (Crime Science Technology), claim to be compatible with DNA analysis as they reduce the need for post-staining to increase contrast of the developed fingermark. The aim of this study was to determine the impact that these one-step luminescent cyanoacrylates have on DNA analysis and how they compare to conventional CA techniques. Four donors each deposited five sets of natural fingermarks, to which a known amount of washed saliva cells was dispensed onto half of each set of fingermarks. Each set was treated with either a conventional CA technique or a one-step luminescent CA technique prior to collection and processing of DNA, with one set left as a non-fumed control. It was found that DNA was still recoverable and detectable following each of the treatments. Lumicyano™ had a similar impact on DNA profiles as conventional CA fuming and with post-stain, however, the degradation effect of PolyCyano UV on DNA was greater than the conventional treatments. For quantities of DNA such as that from touch DNA, the use of PolyCyano UV to enhance fingermarks may impact subsequent DNA analysis by causing allele drop out at larger fragment sizes.

Acetone facilitated DNA sampling from electrical tapes improves DNA recovery and enables latent fingerprints development

Electrical tapes (ETs) are a common component of improvised explosive devices (IEDs) used by terrorists or criminal organizations and represent a valuable forensic resource for DNA and latent fingerprints recovery. However, DNA recovery rates are typically low and usually below the minimal amount required for amplification. In addition, most DNA extraction methods are destructive and do not allow further latent fingerprints development. In the present study a cell culture based touch DNA model was used to demonstrate a two-step acetone-water DNA recovery protocol from ETs. This protocol involves only the adhesive side of the ET and increases DNA recovery rates by up to 70%. In addition, we demonstrated partially successful latent fingerprints development from the non-sticky side of the ETs. Taken together, this protocol maximizes the forensic examination of ETs and is recommended for routine casework processing.

Compatibility of DNA IQ™, QIAamp® DNA Investigator, and QIAsymphony® DNA Investigator® with various fingerprint treatments

Latent fingerprint and touch DNA are the two most important contact evidence for individualization in forensic science which provide complementary information that can lead to direct and unequivocal identification of the culprit. In order to retrieve useful information from both fingerprints and DNA, which are usually mingled together, one strategy is to perform fingerprint examination prior to DNA analysis since common DNA sampling technique such as swabbing could disturb or even destroy fingerprint details. Here, we describe the compatibility of three automatic DNA extraction systems, namely, DNA IQ™, QIAamp^® DNA Investigator, and QIAsymphony^® DNA Investigator^®, with respective to the effects of various fingerprint detection techniques. Our results demonstrate that Super Glue fingerprint treatment followed by DNA IQ™ extraction shows better effectiveness in DNA profiling. Aluminum powder dusting offers the least interference to the three DNA extraction systems above. Magnetic powder dusting, on the other hand, strongly impedes DNA recovery. Physical Developer is the most intrusive, which yields profiles with poor quality, including lower peak heights, poor peak height ratios, and poor intra-color balance. In terms of the choice of extraction method, DNA IQ™ system is recommended for sampling after fingerprint treatments, but not the two DNA Investigator systems.

A molecular exploration of human DNA/RNA co-extracted from the palmar surface of the hands and fingers

"Touch DNA" refers to the DNA that is left behind when a person touches or comes into contact with an item. However, the source of touch DNA is still debated and the large variability in DNA yield from casework samples suggests that, besides skin, various body fluids can be transferred through contact. Another important issue concerning touch DNA is the possible occurrence of secondary transfer, but the data published in the literature in relation to the background levels of foreign DNA present on the hand surfaces of the general population are very limited. As the present study aimed at better understanding the nature and characteristics of touch DNA, samples were collected from the palmar surface of the hands and fingers ("PHF" samples) of 30 male and 30 female donors by tape-lifting/swabbing and subjected to DNA/RNA co-extraction. Multiplex mRNA profiling showed that cellular material different from skin could be observed in 15% of the PHF samples. The total amount of DNA recovered from these samples (median 5.1 ng) was significantly higher than that obtained from samples containing skin cells only (median 1.6 ng). The integrity of the DNA isolated from the donors' hands and fingers as well as the prevalence of DNA mixtures were evaluated by STR typing and compared with reference STR profiles from buccal swabs. DNA integrity appeared significantly higher in the male rather than in the female subsample, as the average percentage of the donors' alleles effectively detected in PHF profiles was 75.1% and 60.1%, respectively. The prevalence of mixtures with a foreign DNA contribution ≥20% was 19.2% (30.0% in the female PHF samples and 8.3% in the male PHF samples). The obtained results support the hypothesis that transfer of cellular material different from skin may underlie the occasional recovery of quality STR profiles from handled items. These results also suggest that gender may represent an important factor influencing the propensity of individuals to carry and transfer DNA through hand contact, possibly because of the differences in personal and hygiene habits between males and females.

The Influence of Selected Fingerprint Enhancement Techniques on Forensic DNA Typing of Epithelial Cells Deposited on Porous Surfaces

Fingerprints deposited at crime scene can be a source of DNA. Previous reports on the effects of fingerprint enhancement methods have focused mainly on fingermarks deposited in blood or saliva. Here, we evaluate the effects of fingerprint enhancement methods on fingerprints deposited on porous surfaces. We performed real-time quantification and STR typing, the results of which indicated that two methods (iodine fuming and 1,2-indanedione in ethyl acetate enhancement) had no effect on the quantity of DNA isolated and resultant STR alleles when compared to control samples. DNA quantities and allele numbers were lower for samples enhanced with silver nitrate and 1,2-indanedione in acetic acid when compared to control samples. Based on DNA quantity, quality, and observable stochastic effects, our data indicated that iodine fuming and 1,2-indanedione in ethyl acetate were the preferred options for the enhancement of fingerprints on porous surfaces.

Enhanced genetic analysis of single human bioparticles recovered by simplified micromanipulation from forensic 'touch DNA' evidence

DNA profiles can be obtained from 'touch DNA' evidence, which comprises microscopic traces of human biological material. Current methods for the recovery of trace DNA employ cotton swabs or adhesive tape to sample an area of interest. However, such a 'blind-swabbing' approach will co-sample cellular material from the different individuals, even if the individuals' cells are located in geographically distinct locations on the item. Thus, some of the DNA mixtures encountered in touch DNA samples are artificially created by the swabbing itself. In some instances, a victim's DNA may be found in significant excess thus masking any potential perpetrator's DNA. In order to circumvent the challenges with standard recovery and analysis methods, we have developed a lower cost, 'smart analysis' method that results in enhanced genetic analysis of touch DNA evidence. We describe an optimized and efficient micromanipulation recovery strategy for the collection of bio-particles present in touch DNA samples, as well as an enhanced amplification strategy involving a one-step 5 µl microvolume lysis/STR amplification to permit the recovery of STR profiles from the bio-particle donor(s). The use of individual or few (i.e., "clumps") bioparticles results in the ability to obtain single source profiles. These procedures represent alternative enhanced techniques for the isolation and analysis of single bioparticles from forensic touch DNA evidence. While not necessary in every forensic investigation, the method could be highly beneficial for the recovery of a single source perpetrator DNA profile in cases involving physical assault (e.g., strangulation) that may not be possible using standard analysis techniques. Additionally, the strategies developed here offer an opportunity to obtain genetic information at the single cell level from a variety of other non-forensic trace biological material.

An evaluation of the transfer of saliva-derived DNA

Studies of DNA transfer have focused largely on the transfer of sloughed off epithelial cells from individuals' hands. This research examines primary, secondary, and tertiary transfer events involving DNA originating from saliva, a commonly encountered body fluid. More routine human behaviors were simulated to evaluate transfer, and the effects of drying time, moisture, and surface composition were investigated. The results agree with previous findings which indicate that the presence of moisture, as well as a smooth nonporous surface as the primary substrate, increases the efficiency of transfer. Previous transfer studies have found that the last individual to come into contact with an item is usually the major contributor to the resulting DNA mixture, unless conditions are simulated in which a "good shedder" serves as the primary depositor and a poor shedder serves as the secondary depositor. The results of this study indicate that when saliva is the source of the transferred DNA, the primary depositor is often the major contributor. These findings suggest that shedder status is less relevant with regard to touch DNA samples in a forensic setting and emphasize the need for caution when analyzing such samples.

Forensic trace DNA: a review

DNA analysis is frequently used to acquire information from biological material to aid enquiries associated with criminal offences, disaster victim identification and missing persons investigations. As the relevance and value of DNA profiling to forensic investigations has increased, so too has the desire to generate this information from smaller amounts of DNA. Trace DNA samples may be defined as any sample which falls below recommended thresholds at any stage of the analysis, from sample detection through to profile interpretation, and can not be defined by a precise picogram amount. Here we review aspects associated with the collection, DNA extraction, amplification, profiling and interpretation of trace DNA samples. Contamination and transfer issues are also briefly discussed within the context of trace DNA analysis. Whilst several methodological changes have facilitated profiling from trace samples in recent years it is also clear that many opportunities exist for further improvements.

Validation of testing and interpretation protocols for low template DNA samples using AmpFlSTR Identifiler

AIM

To test the reliability, robustness, and reproducibility of short tandem repeat (STR) profiling of low template DNA (LT-DNA) when employing a defined set of testing and interpretation parameters.

METHODS

DNA from known donors was measured with a quantitative real time polymerase chain reaction (PCR) assay that consistently detects less than 1 pg/microL of DNA within a factor of 0.3. Extracts were amplified in triplicate with AmpFlSTR Identifiler reagents under enhanced PCR conditions. Replicates were examined independently and alleles confirmed using a consensus approach. Considering observed stochastic effects inherent to LT-DNA samples, interpretation protocols were developed and their accuracy verified through examination of over 800 samples.

RESULTS

Amplification of 100 pg or less of DNA generated reproducible results with anticipated stochastic effects. Down to 25 pg of DNA, 92% or more of the expected alleles were consistently detected while lower amounts yielded concordant partial profiles. Although spurious alleles were sometimes observed within sample replicates, they did not repeat. To account for allelic dropout, interpretation guidelines were made especially stringent for determining homozygous alleles. Due to increased heterozygote imbalance, stutter filters were set conservatively and minor components of mixtures could not be resolved. Applying the resultant interpretation protocols, 100% accurate allelic assignments for over 107 non-probative casework samples, and subsequently 319 forensic casework samples, were generated.

CONCLUSION

Using the protocols and interpretation guidelines described here, LT-DNA testing is reliable and robust. Implementation of this method, or one that is suitably verified, in conjunction with an appropriate quality control program ensures that LT-DNA testing is suitable for forensic purposes.