Biology Reference
In-Depth Information
starch solution; iodine is then added and if the starch has been broken down the
solution will be clear, whereas if starch is still present the colour will be blue. The
technique is not widely used as more sensitive assays have been developed using
modified starch that is covalently linked to a dye, such as cibachron blue or procion
red, to form an insoluble complex [43 - 45]; in the presence of
-amylase activ-
ity the dye is released from the complex and becomes soluble. The release of the
dye causes a colour change that can easily be detected, either in solution or by its
ability to migrate through an otherwise impermeable barrier, such as paper [43 - 45]
(Figure 3.7). Amylases are present in other body fluids such as sweat, vaginal fluid,
breastmilk and pancreatic secretions; however, amylase is present in saliva at con-
centrations greater than in other body fluids [44, 46]. The process takes at least
30 minutes to complete and, unlike the tests for blood and SAP for semen, can only
be performed in the laboratory. The test for saliva is only used in specific tests, such
as oral sexual assault cases.
α
Confirmatory tests
Until recently there were no readily used confirmatory tests for saliva. As with blood
and semen, antibody tests, using lateral flow strips, have been developed that are spe-
cific for saliva [47 - 49]. mRNA can also be isolated from saliva; detection of several
transcripts can provide confirmation that a stain contains saliva [23, 24, 50, 51].
Epithelial cells
When an object is touched, epithelial cells may be deposited [6]. The amount of
cellular material transferred depends upon the amount of time the skin is in contact
with the object, the amount of pressure applied, and the presence of fluid such as
sweat to mediate the transfer. Some people transfer their skin cells more readily than
others; these people are classified as good shedders [9]. This material can be collected
from evidential material by swabbing or by tape lifting [52, 53]. Surfaces that the
perpetrator(s) of a crime are likely to have had contact with include door handles, the
ends of ligatures [54], the handles of weapons and contact marks on victims. These
are all potential sources of epithelial cells [55]. In most cases the number of cells
is very low and the success rate of DNA profiling is limited. Screening methods,
for example using the reagent ninhydrin, which detects the presence of amino acids
(and is routinely used to develop latent fingerprints), can be helpful in identifying
samples that are likely to contain epithelial cells [56]. Epithelial cells, as with saliva
and semen stains, may fluoresce at different wavelengths of light compared with the
background substrate and can be enhanced under some conditions [10, 11, 57].
Evidence collection
The success in finding biological material depends upon the search method employed
and also on the integrity and state of the scene. In the UK, biological material is
