Biology Reference
In-Depth Information
Figure 3.6
The lateral flow immunology test shows two bands in a positive test whereas in a
negative test only one band is present. Positive tests are shown from left to right for blood, semen,
saliva. A test is also available for urine
Semen
Semen comprises mature sperm (spermatozoa) suspended in a fluid secreted from
the prostate gland, seminal vesicles, Cowper's gland and the glands of Littre
[16]. The positive identification of semen can be extremely important evidence to
support an allegation of sexual assault and both presumptive and definitive tests are
commonly used.
Presumptive tests
As with blood, ALS can be a powerful technique to locate and presumptively
identify semen. Semen produces strong photoluminescence over a range of
wavelengths - exposed to UV light it will emit blue photoluminescence that will
be visible to the naked eye [10, 11, 33]; as with other ALS-based methods false
positives are detected [11, 33, 34].
A simple, and commonly used, test involves assaying for the presence of the
enzyme seminal acid phosphatase (SAP), which is present in high concentrations in
seminal fluid [16]. Other body fluids, such as saliva and vaginal secretions, contain
the enzyme albeit in significantly lower concentrations and so can give a positive
