Toward Analysis at the Point of Need: A Digital Microfluidic Approach to Processing Multi-Source Sexual Assault Samples

Forensic case samples collected in sexual assaults typically contain DNA from multiple sources, which complicates short-tandem repeat (STR) profiling. These samples are typically sent to a laboratory to separate the DNA from sperm and non-sperm sources prior to analysis. Here, the automation and miniaturization of these steps using digital microfluidics (DMF) is reported, which may eventually enable processing sexual assault samples outside of the laboratory, at the point of need. When applied to vaginal swab samples collected up to 12 h post-coitus (PC), the new method identifies single-source (male) STR profiles. When applied to samples collected 24-72 h PC, the method identifies mixed STR profiles, suggesting room for improvement and/or potential for data deconvolution. In sum, an automated, miniaturized sample pre-processing method for separating the DNA contained in sexual assault samples is demonstrated. This type of automated processing using DMF, especially when combined with Rapid DNA Analysis, has the potential to be used for processing of sexual assault samples in hospitals, police offices, and other locations outside of the laboratory.

Review of direct PCR and Rapid DNA approaches to streamline sexual assault kit testing

Crime laboratories have been faced with large casework backlogs due to lengthy processing times, limited resources and scientists, and rising crime rates. Evidence related to sexual assault crimes, specifically sexual assault kits (SAKs), heavily contribute to the reported backlogs. Although more sensitive, faster chemistries and automated techniques have been implemented over the years, the traditional STR workflow remains relatively unchanged. Enhanced workflows such as direct PCR and Rapid DNA have the potential to streamline the processing of forensic evidence items including those commonly submitted in SAKs, but the FBI QAS guidelines restrict CODIS-approved labs from implementing these methods for forensic samples. Recent studies have shown decreased turnaround times and improved or comparable profiling success with both approaches. However, review of the literature shows a lack of in-depth research comparing traditional DNA workflows to faster and more sensitive direct PCR and/or Rapid DNA approaches for evidentiary samples, especially for SAKs. By providing the forensic science and criminal justice communities with the strengths and limitations of direct PCR and Rapid DNA methods, stakeholders and policy makers may be better informed.

Development and validation of a novel method "SpermX™" for high throughput differential extraction processing of sexual assault kits (SAKs) for DNA analysis

The Sperm X method uses a nanotechnology derived polymer membrane that functions as a separation medium to effectively trap sperm cells while enabling efficient flow through of the digested epithelial cell DNA. This specialized membrane enabled development of a method that could significantly increase a forensic laboratory's ability to obtain male sperm fraction DNA profiles. The SpermX device provides a rapid, reproducible procedure that is easy to implement in a single-tube format as well as high-throughput truly automated hands-free workflows. Validation studies, performed using the manual SpermX method, include sensitivity, stability, precision (reproducibility and repeatability), mixtures, and a method comparison to the traditional differential extraction. Sensitivity and method comparison studies demonstrated a wide range of sperm cells, from a high of over 2.78 million cells (9158 ng) to a low of 25 cells (83 pg), can be trapped by the SpermX membrane. Stability studies on various substrates (i.e., carpet, cotton, denim, polyester, and silk) and degraded semen gave the expected male DNA profiles. Data from the same operator and a different operator were consistent with low variance. Mixtures, with ratios ranging from approximately 10:1-18182:1, created to simulate real casework type samples including buccal/semen, vaginal epithelial/semen, and post coital swabs at different time intervals, were tested. A comparison of the SpermX method to the conventional differential extraction method resulted in comparable probative male profile allelic data and associated statistical probabilities. For low level sperm samples, down to 25 sperm cells (83 pg), the SpermX method outperformed the conventional differential extraction with more genotypic information and associated probabilities.

A portable sperm cell purification instrument based on continuous flow acoustophoretic separation of sperm cells for on-site forensic sample pretreatment

Obtaining a purified male sperm specimen from the original forensic sample mixtures is a critical procedure in identifying the criminal suspect in the forensic analysis of sexual assault crimes. Differential extraction (DE) has been used as the gold standard for extracting DNA preferentially from sexual assault samples, however it is laborious, time-consuming and inefficient. In this report a continuous flow two-step acoustic cell separation scheme is proposed for the removal of cell debris and cell-free genomic contaminants, followed by separation of sperm cells from epithelial cells. Based on the above method, a portable forensic sperm cell purification instrument has been constructed for on-site pretreatment of forensic samples in sexual assault crimes, where removal of contaminants and isolation of sperm cells could be automatically performed without the use of cell lysis buffer.

Interpol review of forensic science management literature 2016-2019

This paper reviews and summarizes the forensic management literature from late 2016 to late 2019, covering laboratory decision making, business strategy, and industry identity and transparency. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Analytical approaches to differential extraction for sexual assault evidence

Many forensic laboratories face growing demands for the processing of DNA evidence from sexual assault investigations. In these cases, evidence collected from the crime scene or from the victim in the form of a Sexual Assault and Evidence Collection Kit (SAECK) typically contains a mixture of cells from at least two donors. Isolation of DNA contributions to link a sample to an alleged offender requires precise chemical treatment of each sample with the goal of separating epithelial cells from non-sperm cells. Currently, the vast majority of laboratories employ differential chemical lysis methods that require lengthy incubations and several manual steps, preventing complete automation. Numerous alternative methods for the differential extraction (DE) of sexual assault evidence have been developed to provide a solution to the growing backlog of samples observed in the US and other countries. Here, we will discuss the predominant methodology for the DE of DNA from sexual assault samples and review alternative approaches from literature. We illustrate three criteria that provide a measure of success in performing these types of chemical separations and examine all methods based upon these expectations. We conclude by providing some general insight into the application of DE techniques in forensic laboratories and discuss the potential future directions of alternative technologies.