https://www.floridaforensicscience.com/wp-content/uploads/2017/02/DNA-Transfer-During-Laundering-May-Yield-Complete-Genetic-Profiles.pdf
Noel S et al., Forensic Science International: Genetics 23 (2016) 240–247
"For each of the seven bed sheet experiments, a 1 cm
2 cutting from the front of one randomly selected pair of underwear was tested for the presence of seminal fluid using the Brentamine Fast Blue B salt test (AP, Sigma-Aldrich) and the ABAcard1 p30 (PSA, Abacus)."
"AP and PSA testing in underwear washed with two, six or ten ejaculates were all negative. These serological tests were also negative in control children’s underwear, even when a cutting produced a partial genetic profile within the sperm fraction. Positive presumptive testing with an associated male profile in the sperm fraction can thus generally be interpreted as an indication that semen was deposited directly onto the fabric rather than transferred during the wash."
The fast blue B salt test works as follows: Semen contains an enzyme called acid phosphatase (AP). When it hydrolyzes an artificial substrate a nucleophilic compound is released that attacks the diazonium group (the electrophile) of fast blue B. This creates a compound (a type of azo dye) that is purple colored, a positive result. The ABAcard p30 test uses antibodies to bind to a protein of 30,000 in molecular weight. It is a type of lateral diffusion immunoassay:
https://projects.nfstc.org/workshops/resources/msds/linked%20documents/ABAcard%20p30%20Test%20for%20the%20Forensic%20Identification%20of%20Semen.pdfSuzanna Ryan
wrote, "The possibility of transfer of sperm cells should be carefully considered, especially if the area where the sperm cell(s) are collected is: 1. AP negative (AP is an enzyme that loses its reactivity when exposed to water. If an item has been washed, sperm cells may still be present, but it is unlikely that the AP test would yield a positive result.)"
It is important to distinguish DNA profiling from the body fluid testing. The take-home message here is that
neither test performed in the 2016 paper gave an indication that seminal fluid could be transferred from a sheet onto underwear. Sperm heads are a different matter.