Frequently Asked Questions
Can I make mock samples for a sensitivity study using diluted semen?
Yes, but the semen must be fresh. Serial dilutions can be created using freshly collected semen (not frozen or stored). For best results, dilute the semen in 1X PBS and vortex for 20 seconds to mix. All pipetting steps should be performed immediately after vortexing. The mock samples may be made from each dilution and should be spotted onto the substrate as soon as possible after dilution. As soon as the sperm cells are dry, they are stable and will closely represent normal forensic casework.
Diluted semen should not be stored for later use with Erase. Stored neat semen and stored semen dilutions do not create mock samples that behave the same way as casework samples when using the Erase Sperm Isolation Kit.
Should I purchase frozen semen for use in testing?
No, purchasing semen is problematic because often samples have been subjected to multiple freeze-thaw events and also contain preservatives.
Are there any casework samples that I should not use Erase on?
Although Erase routinely outperforms standard differential extractions with most sexual assault evidence and post coital samples, using Erase as the first method of testing on any case where the evidence sample was recovered from a body and/or article in water (lake, river, etc.) or from severely decomposed remains is not currently recommended.
Is there a source for mock swabs so that I don’t have to make them?
PTC works with an infertility clinic (in conjunction with their patients) that provides a source of post-coital swabs. Those swabs are available for validation purposes if you think they might be helpful in your studies.
If your laboratory does not have a readily available means for producing mock swabs for a sensitivity study or substrate study, please contact PTC and we will try to accommodate your needs.
Are there any substrates that Erase has been found not to work with?
Substrate studies have been completed and Erase has been show to successfully work with the following items: condoms, tampons, sanitary napkins, denim, black/blue cotton, white nylon and blood. There are no known substrates that present a problem when used with Erase.
How long does it take to complete a differential extraction with Erase?
Completing an Erase extraction takes about 2 hours of actual time and about 10 minutes of hands on time. The sample is then ready for DNA purification.
Does my sample have to be DNA purified after Erase?
Yes. Currently Erase has been shown to be compatible with the EZ1/Symphony, Maxwell and PCIA purification methods. Although, we expect that other purification methods will work but they have not been tested.
Can Erase be automated on my liquid handler?
Erase can be automated on any liquid handler. Please contact PTC for programming assistance.
Has Erase been tested with old samples?
Yes. Erase has been successfully tested on 15 year old post coital samples that have been stored at room temperature.
Does Erase work when the vaginal swabs are not collected for many hours or days after the sexual assault?
Yes. Erase is very helpful in these situations. Even when there are very few sperm cells as compared to epithelial cells, it is usually possible to obtain a sperm DNA profile from the sperm fraction of an Erase differential extraction.
Please contact us if you have any further questions.