Evaluating novel and conventional cell-separation techniques for sexual assault investigations

Abstract

Biological evidence from sexual assaults frequently includes few male cells (i.e., spermatozoa) and numerous female cells (i.e., epithelial cells). In practice, their genetic analysis typically involves separating the victim's cells from the perpetrator's sperm using conventional differential extraction or advanced cell enrichment/capturing techniques. A descriptive study on simulated sexual assault samples was carried out by the recruitment of 10 heterosexual, monogamous couples. Post-coital swabs were collected before and after consensual sexual intercourse, with a sampling period of up to 96 h, and subjected to analysis to detect, quantify, and genotype adhering sperm by three distinct cell-separation techniques: differential extraction, laser capture microdissection, and DEPArray™. Methods differed in sperm detection and genotyping efficacy, while foreign DNA was identifiable up to 96 h. Time since intercourse and individuals were statistically significant factors (p ≤ 0.05) on male DNA yields, while hygienic behavior was not. Prior sperm enrichment was pivotal for cell capture technologies to counteract the abundance of epithelial cells, achieved by a prior mild digestion step for laser microdissection. Evaluating the advantages and disadvantages of standard and advanced methods provided a novel, comprehensive understanding of their merits, postulating that modern applications can assist conventional ones in challenging crime samples.