At Cellmark Forensic Services, innovation is at the heart of our mission to improve forensic outcomes. As part of our ongoing research and development commitment, we are proud to announce a validated enhanced recovery technique that significantly improves the extraction of sperm cells and DNA from exhibits containing superabsorbent polymers (SAPs), materials commonly found in disposable hygiene products such as sanitary pads and nappies.
Why SAPs matter in forensic investigations
Sanitary pads, nappies, and similar products worn during or shortly after a sexual assault can hold critical biological evidence. These items are designed with multiple layers to absorb and distribute fluids and often include SAPs. SAPs are water-absorbing molecules capable of retaining large volumes of liquid relative to their mass. This means that blood, urine, and other body fluids, including semen, are absorbed deep within the SAP-containing layer, making recovery challenging.
The forensic challenge
Traditional extraction techniques, including our established Sperm Elution process, have been highly effective for non-SAP layers. However, when SAPs are present, samples often form a gel-like substance that cannot be processed further. As such, only the upper layer(s) of such items can be examined for the presence of semen and DNA, limiting recovery and potentially impacting on evidential outcomes.
The Breakthrough
Our modified Sperm Elution technique now overcomes this barrier. By adapting the process for SAP containing layers, we can maximise the recovery of sperm cells and cellular DNA without affecting downstream presumptive tests or DNA profiling.
The Results
- Sanitary Pads: Incorporating SAP layers into extraction resulted in approximately double the sperm cell recovery compared to non-SAP layers.
- Nappies: On average, approximately four times more sperm cells were recovered using the enhanced process. However, the recovery from nappies of different brands was variable, with almost twenty times the amount of sperm cells recovered when incorporating the SAPs layer compared to extracting the top layer only for some of the tested nappies.
- Additional Findings: The technique also successfully recovered cellular DNA from SAP layers when saliva, rather than semen, was deposited. This would also likely assist in recovering DNA from the source of any azoospermic semen should this be deposited onto such items.
What This Means for Casework
Our Biology Reporting Scientists are fully briefed on this new method and can recommend its application for current or new submissions. For cases already examined and reported where exhibits remain available, re-examination may now be possible—potentially improving evidential outcomes.
If you would like further information, please email forensicsales@cellmark.co.uk or use the contact form below. Alternatively, to visit our page on our sexual offence service please click here.