Forensic Biology and Biological Fluids

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Table of Contents

Delivering of Evidence to the Lab for Testing
Forensic Examination of Collected Body Fluids
Similarity and Difference between the Tests for the Three-Body Fluids
References

Delivering of Evidence to the Lab for Testing

After the physical evidence comprising of broken glass, statins from carpet, furniture, and clothing, and drinking glasses, has been appropriately collected and packaged, it is then transported to the crime laboratory for analysis. Often, evidence obtained from a scene is presented to the investigator-on-case with the proper documentation and a brief explanation of how it was collected. The investigator-on-case then determines which evidence should require further lab examination (Washington State Patrol, 2015).

Several methods are used to deliver evidence; however, the method selected is dependent on the size and type of the item, the complexity, and the urgency of the case (Washington State Patrol, 2015). Regardless of the method employed, it is vital to ensure that evidence is not lost, damaged, or contaminated. Furthermore, the chain of custody should be kept as short as possible. Personal delivery is the most recommended method as it shortens the length of the chain of custody.

The other way is delivery by the use of a common carrier, for example, the U.S. Postal Service. When using carrier services, it is necessary to request a formal notification on delivery or sent by Registered Mail with a return receipt requested. Moreover, the investigator should begin by checking with the local and state crime laboratories to determine where evidence should be sent. This is because most laboratories analyze controlled substances; nevertheless, certain types of examinations involving glass and latent print analysis are performed at specific laboratories.

Forensic Examination of Collected Body Fluids

Blood

Blood comprises cells, proteins, enzymes, water, and inorganic substances. Three steps have to be followed by the forensic serologists when presented with stains from clothing, furniture, and carpet. First, the analyst performs a presumptive test to determine if the stain is blood. The principle of the presumptive test is based on hemoglobin’s ability to oxidize specific reagents, therefore, bringing about a color change (Gefrides & Welch, 2011).

The oxidizing agent is often hydrogen peroxide. In the case of invisible stains, the luminol test is conducted. It is often utilized in large areas, where blood is suspected but invisible. The bloodstain will glow in the presence of blood (Gefrides & Welch, 2011). Luminol is highly sensitive and lacks false positives. However, in instances where there are visible stains, the Kastle-Meyer (KM) and leukomalacia green (LMG) tests, are applied. The KM or phenolphthalein test is a popular presumptive catalytic method. A phenolphthalein indicator solution is applied to the suspected bloodstain, followed by hydrogen peroxide.

A bright pink color is indicative of blood (Gefrides & Welch, 2011). Nevertheless, it yields a false positive with other substances, such as chemical oxidants and fruit or vegetable peroxidases. It is also not as sensitive as the luminol test. On the other hand, the LMG test is performed in a manner similar to the KM test and results in blue-green color in the presence of blood (Gefrides & Welch, 2011).

Since some presumptive tests have false positives, and they are not species-specific, it is essential to determine whether or not it is human blood using a confirmatory test. An example of a popular confirmatory test is the precipitin test (Gefrides & Welch, 2011). In this test, an animal is injected with human blood, after which it forms antibodies in response to the antigens in human blood. The antibodies are then obtained from the animal’s blood serum, antiserum, and placed in a test tube. An extract from the bloodstain is then added to the serum – the formation of a precipitate at the boundary of the meeting point is indicative of human blood.

The last step is for the serologist to determine if the blood can be associated with an individual, for instance, by performing a blood typing or DNA test. On the surface of erythrocytes are proteins referred to as antigens, which are partially used to identify individuals. Human erythrocytes have several antigens; however, the Rhesus (Rh), A, B, and O are commonly used (Gefrides & Welch, 2011). Blood typing entails the determination of the antigens present in a blood sample.

This is achieved by the use of an enzyme-linked immunosorbent assay (ELISA) in which the agglutination of the suspected blood and a certain antiserum illustrates the presence of a particular blood type (Gefrides & Welch, 2011). A further DNA test can be conducted to determine if the blood belongs to a specific individual. This is usually done by generating the DNA profile of the suspected bloodstain and comparing it to that of the victim and suspect.

Semen

Seminal fluid is a mixture of spermatozoa, enzymes, water, and inorganic salts. The several presumptive tests that can be performed comprise using the ultra-violet (UV) light and the acid phosphatase test (Gefrides & Welch, 2011). In the first test, a source of UV light is illuminated over the stain, and a luminescence suggests the presence of blood. However, it yields false positives with other substances, such as ointments, creams, and blood. On the other hand, the principle of the acid phosphatase test relies on the ability of the enzyme, acid phosphatase, to catalyze the hydrolysis of Alpha-Naphthyl acid phosphate.

This will lead to the formation of a product that reacts with Brentamine Fast Blue to produce a purple color when semen is present. However, the rate of color change depends on the concentration of seminal fluid. Lastly, Lastly, Protein Specific Antigen (PSA) test entails the analysis of the PSA, which is a protein that is exclusively present in seminal fluid. Moreover, the test can apply to cases involving azoospermic or vasectomized individuals. The formulation of a purple color evidences a positive reaction.

The most reliable and popular confirmatory tests consist of the microscopic visualization of sperm and DNA analysis. In microscopic visualization, a Christmas tree stain has to be first applied to semen, then the sample viewed under a microscope. The Picroindigocarmine gives the neck and tail sections of the sperm a green and blue color, while Nuclear Fast Red stains the sperm’s head red with the tip of the head, the acrosomal cap, pink (Gefrides & Welch, 2011). On the other hand, DNA analysis involves Y-STR analysis in which uses the Y chromosome to determine the individual who is the source of the semen.

Saliva

Saliva contains buccal cells, water, mucin, and amylase. There are fewer presumptive tests for the identification of saliva; however, there are currently no confirmatory tests, which are specific to saliva (Gefrides & Welch, 2011). Saliva samples can be obtained from the drinking glasses. Similar to semen and blood, saliva can also be detected under ultra-violet light. Nevertheless, the most popular technique of presumptively testing for saliva is the starch-iodine test. The principle of this test is influenced by the ability of enzyme amylase to hydrolyze starch. Therefore, when starch, iodine, and a sample of the suspected saliva are mixed, amylase present in saliva hydrolyzes starch resulting in the deep blue-black color that was formed from the reaction of starch and iodine to fade.

Similarity and Difference between the Tests for the Three-Body Fluids

In both body fluids, presumptive tests are conducted. Moreover, when using alternate light sources, such as UV light, all fluids illuminate. However, since the tests are influenced by distinct components of the body fluids, the types of tests performed are different.

References

Gefrides, L., & Welch, K. (2011). Forensic biology: Serology and DNA. In A. Mozayani & C. Noziglia (Eds.), The forensic laboratory handbook: Procedures and practice (pp. 15-50). Totowa, NJ: Humana Press.

Washington State Patrol. (2015). Forensic services guide. Web.

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