Screening of sexual assault evidence for semen can be a bottleneck in the forensic lab due to difficulties spotting sperm cells under a microscope. The dyes typically used to stain a potential semen sample are not always sensitive and specific enough to make sperm cells stand out, especially when a sample may be old or degraded. Researchers from King’s College London and the University of Warwick sought to greatly speed up this screening process through the development of aptamers that selectively binds to human sperm.
The aptamers, single-stranded DNA molecules that bind to a specific target molecule, were demonstrated to selectively bind to sperm cells over other cell types; combined with a fluorescent tag, the aptamers help make sperm cells much more visible under a microscope. The research team used the Cell-SELEX (systematic evolution of ligands by exponential enrichment) protocol along with massively parallel sequencing to identify the most promising aptamer candidates and used microscale thermophoresis and enzyme-linked oligonucleotide assays to demonstrate their selective binding capabilities. The study was published in Analytical and Bioanalytical Chemistry.
“Such a technique would likely result in a drastic reduction in the cost and amount of time needed to screen items of evidence for semen in cases of sexual assault, as well as prevent the possibility of missed evidence—and therefore potential miscarriages of justice,” said lead author James Gooch from the School of Cancer & Pharmaceutical Sciences at King’s College.
The researchers are working to further optimize the aptamer candidates to make them even more specific. The optimized sequences will then undergo validation procedures, allowing forensic laboratories to take advantage of this new resource for sexual assault kit screening.
Photo: Microscopic examination of haemotoxylin and eosin-stained sperm cells (cropped and resized from original image). Credit: James Gooch et al., Analytical and Bioanalytical Chemistry, CC-BY-4.0, https://creativecommons.org/licenses/by/4.0/legalcode