DNA recovery after sequential processing of latent fingerprints on black polyethylene plastic.

Latent fingerprints on plastic substrates can be visualized by using sequential treatments to enhance the contrast between the fingerprint residues and underlying substrate; however, the extent to which these processes affect subsequent DNA analysis is mostly unknown. Latent fingerprints deposited on black plastic by one donor were visualized with single-process fingerprint powders (i.e., white powder, bichromatic powder, or bichromatic magnetic powder) or sequential treatments (i.e., laser → reflected ultraviolet imaging system (RUVIS) → CA fuming → RUVIS → Rhodamine 6G, Ardrox, and MBD (RAM) or CA fuming → RAM/laser → bichromatic magnetic powder). Samples were examined after the addition of each treatment. DNA was collected using cotton swabs, extracted, quantified, and amplified. DNA yields, peak heights, number of alleles obtained, and percentage of DNA profiles eligible for CODIS upload were examined. Latent fingerprints processed with the laser and up to three sequential treatments generated DNA profiles with significantly higher peaks heights than those of the untreated samples. Fingerprints processed with the laser and up to two sequential treatments generated DNA profiles with significantly more alleles. All methods beginning with laser enhancement generated more CODIS-eligible profiles. Additional research is needed to determine the extent to which initial laser enhancement impacts the success of downstream DNA profiling results. Although DNA profile development is not guaranteed due to the variable quantities of DNA contained within latent fingerprints, the selection of an appropriate latent fingerprint visualization method could maximize both fingerprint detection and the generation of CODIS-eligible DNA profiles.

DNA recovery after sequential processing of latent fingerprints on copy paper.

Forensic examiners must determine whether both latent fingerprint development and DNA profiling can be performed on the same area of an evidence item and, if only one is possible, which examination offers the best chance for identification. Latent fingerprints can be enhanced by targeting different components of fingerprint residues with sequential chemical treatments. This study investigated the effects of single-reagent and sequential latent fingerprint development processes on downstream DNA analysis to determine the point at which latent fingerprint development should be stopped to allow for DNA recovery. Latent fingerprints deposited on copy paper by one donor were developed using three sequential processes: 1,8-diazafluoren-9-one (DFO) â†’ ninhydrin â†’ physical developer (PD); 1,2-indanedione-zinc (IND-Zn) â†’ ninhydrin â†’ PD; and IND-Zn â†’ ninhydrin â†’ Oil Red O (ORO) â†’ PD. Samples were examined after the addition of each chemical treatment. DNA was collected with cotton swabs, extracted, quantified, and amplified. DNA yields, peak heights, number of alleles obtained, and percentage of DNA profiles eligible for CODIS upload were examined. DNA profiles were obtained with varying degrees of success, depending on the number and type of treatments used for latent fingerprint development. The treatments that were found to be the least harmful to downstream DNA analysis were IND-Zn and IND-Zn/laser, and the most detrimental treatments were DFO, DFO/laser, and PD. In general, as the number of treatments increase, the opportunities for DNA loss or damage also increase, and it is preferable to use fewer treatments when developing latent fingerprints prior to downstream DNA processing.

Determining the number of contributors to DNA mixtures in the low-template regime: Exploring the impacts of sampling and detection effects.

The interpretation of DNA evidence may rely upon the assumption that the forensic short tandem repeat (STR) profile is composed of multiple genotypes, or partial genotypes, originating from n contributors. In cases where the number of contributors (NOC) is in dispute, it may be justifiable to compute likelihood ratios that utilize different NOC parameters in the numerator and denominator, or present different likelihoods separately. Therefore, in this work, we evaluate the impact of allele dropout on estimating the NOC for simulated mixtures with up to six contributors in the presence or absence of a major contributor. These simulations demonstrate that in the presence of dropout, or with the application of an analytical threshold (AT), estimating the NOC using counting methods was unreliable for mixtures containing one or more minor contributors present at low levels. The number of misidentifications was only slightly reduced when we expand the number of STR loci from 16 to 21. In many of the simulations tested herein, the minimum and actual NOC differed by more than two, suggesting that low-template, high-order mixtures with allele counts fewer than six may be originating from as many as four-, five-, or six-persons. Thus, there is justification for the use of differing or multiple assumptions on the NOC when computing the weight of DNA evidence for low-template mixtures, particularly when the peak heights are in the vicinity of the signal threshold or allele counting methods are the mechanism by which the NOC is assessed.

Assessment of the stability of DNA in specimens collected under conditions for drug testing-A pilot study.

For forensic biological sample collections, the specimen donor is linked solidly to his or her specimen through a chain of custody (CoC) sometimes referenced as a chain of evidence. Rarely, a donor may deny that a urine or oral fluid (OF) specimen is his or her specimen even with a patent CoC. The goal of this pilot study was to determine the potential effects of short-term storage on the quality and quantity of DNA in both types of specimen under conditions that may be encountered with employment-related drug testing specimens. Fresh urine and freshly collected oral fluid all produced complete STR profiles. For the "pad" type OF collectors, acceptable DNA was extractable both from the buffer/preservative and the pad. Although fresh urine and OF produced complete STR profiles, partial profiles were obtained after storage for most samples. An exception was the DNA in the Quantisal OF collector, from which a complete profile was obtained for both freshly collected OF and stored OF.

Rapid detection and strain typing of Chlamydia trachomatis using a highly multiplexed microfluidic PCR assay.

Nucleic acid amplification tests (NAATs) are recommended by the CDC for detection of Chlamydia trachomatis (Ct) urogenital infections. Current commercial NAATs require technical expertise and sophisticated laboratory infrastructure, are time-consuming and expensive, and do not differentiate the lymphogranuloma venereum (LGV) strains that require a longer duration of treatment than non-LGV strains. The multiplexed microfluidic PCR-based assay presented in this work simultaneously interrogates 13 loci to detect Ct and identify LGV and non-LGV strain-types. Based on amplified fragment length polymorphisms, the assay differentiates LGV, ocular, urogenital, and proctocolitis clades, and also serovars L1, L2, and L3 within the LGV group. The assay was evaluated in a blinded fashion using 95 clinical swabs, with 76 previously reported as urogenital Ct-positive samples and typed by ompA genotyping and/or Multi-Locus Sequence Typing. Results of the 13-plex assay showed that 51 samples fell within urogenital clade 2 or 4, 24 samples showed both clade 2 and 4 signatures, indicating possible mixed infection, gene rearrangement, or inter-clade recombination, and one sample was a noninvasive trachoma biovar (either a clade 3 or 4). The remaining 19 blinded samples were correctly identified as LGV clade 1 (3), ocular clade 3 (4), or as negatives (12). To date, no NAAT assay can provide a point-of-care applicable turnaround time for Ct detection while identifying clinically significant Ct strain types to inform appropriate treatment. Coupled with rapid DNA processing of clinical swabs (approximately 60 minutes from swab-in to result-out), the assay has significant potential as a rapid POC diagnostic for Ct infections.