The author reports on a research project that was developed to address the backlogs of sexual assault casework throughout the US by developing a new differential extraction (DE) protocol to expedite, without compromising quality, the processing of sexual assault samples.
The author reports on a project that was designed to adapt, optimize, validate, and integrate a DNase I differential extraction protocol (DNase DE) into the current sexual assault casework workflow on the Beckman Coulter Biomek® NXP (NXP) automation workstations at the Virginia Department of Forensic Science (VADFS). The project focused on integrating three published manual DNase I-based protocols with current VADFS manual sexual assault DE protocol to generate a semi-automated method of performing sperm pellet clean-up, without the need for numerous pellet washes, thereby developing sperm fraction (SF) and non-sperm fraction (NSF) fractions in a more automated manner. The author addresses the question of how to optimally combine the published DNase DE protocols with the VADFS DE protocol to reduce manual steps and, as a result, the overall time, and to increase throughput. Key outcomes of the optimized semi-automated DNase DE method included: it produced Y-DNA yields and A/Y ratios comparable to the manual VADFS DE method with reduced manual steps involved; the two methods had comparable sensitivities for the SF; it demonstrated reproducibility comparable to the current manual VADFS DE method; it produced STR profiles comparable to the manual VADFS DE method, including being able to generate sole-source male profiles from SF samples; it was impacted by the presence of contaminants comparably to the VADFS DE method; and it had a low cross-contamination frequency similar to the VADFS DE method. The author suggests that the DNase DE meets the criteria for replacing the current VDFS DE method for sexual assault casework.
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