Recovery of spermatozoa from superabsorbent polymers to assist in the forensic interpretation of sexual offences
Student thesis: Doctoral Thesis
Forensic investigation of cases of rape and some sexual assault relies on the successful location and identification of semen from recovered exhibits, typically intimate swabs and clothing. Recovery of semen from most substrates is achieved by simple water extraction methods and microscopic observation of the presence of spermatozoa. However, the superabsorbent polymers (SAPs) used in the manufacture of sanitary protection products, such as nappies and sanitary towels, are specifically designed to retain liquid materials. This property prohibits water extraction, which renders them problematic when seized as exhibits to be examined for evidence in cases of sexually motivated crime. This work sought to identify and develop a method to release semen from the absorbent polymers to allow for DNA analysis to assist with any subsequent investigation. The use of salts both in powder and solution forms were investigated along with the application of pressure. It was established that a 0.5 Molar solution of calcium chloride provided the optimum conditions to release semen from a selected SAP containing product and that a final water washing step facilitated quantitative analysis by microscopy. Full DNA profiles using ESI17 were obtained from semen recovered from samples of SAP containing, ultra sanitary towels which had been stored frozen and also some which had been allowed to air dry overnight after semen deposition to replicate forensic casework samples. Some method optimisation may be required by forensic service providers to adapt it for use in routine casework however, this study has provided a simple, efficient and cost effective method to release spermatozoa from sanitary protection products in order to assist with forensic investigations. The successful completion and implementation of this work could have major implications across the world in providing significant improvements to the investigation of sexual offences.
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