Sexual assault evidence composes a large portion of the evidence analyzed by forensic serologists. Key to the processing of sexual assault evidence is the screening of the evidence items for the presence of semen. Due to the intimate nature of a sexual assault, it is very possible that semen is mixed with other body fluids when it is deposited on an item of evidence. One of the body fluids that semen can easily come into contact with during a sexual assault is saliva. Saliva functions as the first step in the human body’s digestive system. Due to the digestive system’s purpose of breaking down nutrients, it stands to reason that saliva could play a role in breaking down seminal components. To detect semen, specific components of semen are tested for in forensic laboratories. These components are often acid phosphatase, prostate specific antigen, semenogelin, and spermatozoa.
This experiment combined semen from one donor with saliva of seven other donors in a two part survey. In part one, semen was mixed with the saliva of Donors A, B, C, and D at three different ratios of 1:1, 1:2, and 1:10 semen-saliva. Twenty-microliter stains were pipetted onto one inch by one inch squares on twelve cotton swatches to test for acid phosphatase, prostate specific antigen, semenogelin, and spermatozoa. One set of six swatches was allowed to dry and the other set was kept damp. The stains were tested at six timepoints: day zero, day one, week one, week two, week three, and week four. Part two involved incubating the semen with saliva from Donors X, Y, and Z at body temperature for up to twenty-four hours. The same three ratios used in part one were repeated with the saliva from Donors X, Y, and Z in part two. A twenty microliter stain was pipetted onto a cotton swatch at each of the five timepoints from the start of the incubation period: zero minutes, one hour, five hours, eight hours, and twenty-four hours. Each stain was tested for acid phosphatase, prostate specific antigen, and semenogelin.
The results of part one showed that semen samples that are mixed with saliva but allowed to dry are effectively unaffected by the presence of saliva. On the dry swatches, the stains tested positive for every component of semen at every timepoint for every donor except for Donor D’s 1:10 semen-saliva mixture stain, which tested negative for spermatozoa at week 1, but positive for spermatozoa in the subsequent timepoints. The results of the damp swatches suggests that damp environmental factors can prevent the detection of seminal components. By week two, the detection of spermatozoa had completely dropped out in the mixture stains and in the neat semen control stains. Detection of prostate specific antigen ceased in the control by week 3 and had also stopped in all 1:1 semen-saliva mixture stains by week 4. The detection of prostate specific antigen had stopped at week 3 for all donors in the 1:10 semen-saliva mixture stains. Semenogelin was still detectable in the control sample for the duration of the experiment, and it was detected for all donors at week 4 in the 1:1 and 1:2 semen-saliva mixture stains. Detection of semenogelin ceased in Donors B and D in the 1:10 semen-saliva mixture stains by week two.
The results of part two suggested that the detection of acid phosphatase could be affected when semen and saliva have been incubating together at body temperature. Acid phosphatase was detected at all the timepoints in the neat semen control, but after eight hours, it was no longer detectable in all the mixture ratios of Donors X and Z. Acid phosphatase was no longer detectable in the 1:1 semen-saliva mixture stain of donor Y at eight hours and in the 1:2 semen-saliva mixture stain of Donor Y at twenty-four hours. Acid phosphatase did remain detectable in the 1:10 semen-saliva mixture stain of Donor Y through the twenty-four hour experimental period. Prostate specific antigen and semenogelin remained detectable in all the donors at all three ratios for the duration of the experiment.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45551 |
| Date | 31 January 2023 |
| Creators | Gizelbach, Cole Reagan |
| Contributors | Brodeur, Amy N. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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