Progress in sperm cell separation and analytical techniques for semen-epithelial mixed stains: a forensic perspective

The analysis of sperm-epithelial cell mixtures plays a pivotal role in sexual assault investigations, providing critical DNA evidence to detect and match genetic profiles associated with suspects and support legal proceedings. Traditional methods for separating and analyzing semen-epithelial mixed stains often encounter specific challenges, such as trace samples, degraded specimens, or low spermatozoa concentrations. These challenges highlight the need for effective and reliable techniques tailored to address the complexities of these mixtures. This review tackles this issue by comprehensively evaluating a range of innovative methods for isolating and analyzing spermatozoa and epithelial cell components, exploring their applications at both cellular and molecular levels. This review aims to serve as a detailed resource for forensic practitioners, summarizing the characteristics and practical significance of these methods to guide their selection in casework. Key results highlight diverse techniques, including differential extraction, pore size filtration, micro-capture methods, optical tweezers, microfluidic chips, flow cytometry, and immunomagnetic bead separation, each offering unique strengths, such as the precision of microfluidic chips or the cost-effectiveness of immunomagnetic beads, alongside specific limitations. The review concludes that no single method is universally optimal; instead, the choice depends on case-specific factors like sample quality and available resources, emphasizing the need for tailored approaches in particularly complex cases. The application of novel sperm cell separation and DNA analysis techniques promise to enhance the accuracy and efficiency of forensic analyses, potentially reducing lab backlogs, speeding up case resolutions, and improving support for sexual assault victims, thus advancing justice and societal well-being.