Forensic serology is the application of immunological techniques to pin criminals to crime scenes. In other words, it is the use of antigen-antibody reactions to address challenges in the criminal justice system.
Forensic serology is an important branch of criminal investigation besides the other branch which is DNA analysis which uses molecular techniques to identify samples from crime scenes.
Both forensic serology and DNA analysis have something in common – they use the same biological samples to identify criminals and victims.
While forensic serology tries to identify evidence using various body fluids, DNA analysis matches such samples to individuals – criminals and/or victims.
In this article, we shall discuss everything about forensic serology including its history, how it works, what samples it uses, and how it helps to solve criminal investigation challenges.
History of Forensic Serology
For many years in the past, it wasn’t easy to pin suspects to the crime scenes and so they escaped the criminal justice system.
On the other hand, victims went without justice because it wasn’t possible to tell unequivocally who had harmed them. Today, thanks to forensic serology and DNA analysis because if we have some leads and suspects, they hardly escape justice.
They are jailed for life and sometimes hanged depending on the weight of their offenses. Forensic serology has a long history, and we want to explore it briefly here:
The concept of forensic serology is a relatively new concept – born in the 20th century. However, the phrase forensic serology has been around for a while.
Sometimes the phrase “forensic serology” is loosely used to refer to other techniques that are not immunological in nature. Examples of such techniques include enzyme-based techniques and DNA analysis.
DNA analysis is even a newer concept but one that has nearly overtaken all the other methods in forensic science. This is certainly due to its accuracy in individualizing the test results and hence greater power in court case resolution.
Since its discovery, forensic serology has found many applications including helping in partly resolving paternity issues and forensic examination in criminal cases.
How does Forensic Serology Work?
Forensic serology can generally be divided into three phases. The first one is sample collection, followed by sample analysis in the laboratory, and finally the application of the test results in the resolution of issues.
Forensic Serology Test Performance
This test is performed by people who have training in forensic serology or in immunology – the study of the immune system. Though they might also be trained as police officers or forensic scientists, it is important that these professionals understand how antigen-antibody reactions work in vitro.
Sample Collection
The scientists will first collect samples from the crime scenes. These samples are mostly body fluids or swabs of body fluid stains on the crime scene and/or personal belongings of the victims.
A precise list of samples that are used for forensic serology tests includes blood, saliva, breast milk, semen, sweat, mucus, tears, and many other bodily fluids that leak out when a person dies.
While collecting the samples you need to be careful to be sure that the sample will be helpful in forensic serology. Make sure that the sample is not contaminated at all. This is the only way it can help to resolve a court case.
It’s also important to ensure that there is proper documentation accompanying the samples in a manner that cannot create room for mistakes in testing and discourage challenges by lawyers on the credibility of the test results.
Performing the Test in the Laboratory
The test is performed using commercial reagents. The test depends on the type of sample collected from the crime scene. Let’s discuss examples of sample-specific methods of forensic serology here.
Immunochromatography for Blood Detection Tests
Before immunochromatography is performed, when the material in the swab from the crime scene is suspected to be blood, the forensic serologist will first perform a presumptive test to be sure that they are dealing with blood.
The most common test for confirming blood in the test material is the luminol test. In this test, a chemical is sprayed on body fluid stains suspected to be blood. An indication that blood is the likely fluid in the stain is shown by chemiluminescence.
Once such a result is evident, there is a high likelihood that the material you are dealing with is blood, and immunochromatography can now be applied.
Like many other immunological tests, this method works by the antigen-antibody reaction. Commercially procured antibodies are used to detect antigens that could be present in the blood.
The set-up of this test is on a chromatographic paper and the lateral flow of the sample is by capillary action. This test works the same way as sandwich ELISA on the microtiter plate.
This should not be an unfamiliar test but certainly, not one that you have not heard about. The test strip works the same way as the HCG-detecting pregnancy test.
In the immunochromatographic test for the blood sample from the crime scene, the presence or absence of certain antigens in the blood is detected.
Detection of blood antigens can be important when confirming the scene of a homicide or when there is a claim that someone was injured in an altercation or in an attack, yet the suspect denies causing bloodshed.
Further analysis of DNA profiles could help to pin a suspect to the crime scene. It is only then that a court of law adopts the results to help in the determination of the case.
Semen Detection Tests
On matters of rape cases, semen detection is presumptive that there was sex. However, this test can be limited when the male involved is vasectomized or oligospermia.
In such cases, semen will not be detected yet it doesn’t mean that there was no sex. A better test is a confirmatory immunochromatographic test called p30/PSA test.
This test applies the principle of sandwich ELISA and can be performed on a strip set-up like a pregnancy test for HCG mentioned earlier.
This test will detect the presence of p30 which is a prostate-specific antigen found in semen when a man ejaculates during sex.
A positive test confirms that sex occurred but not who was involved. A DNA analysis test is needed to either indict or exonerate a suspect.
Urine Detection Tests
Urine detection begins with the presumptive test for urine mostly using a called para-dimethylaminocinnamaldehyde test abbreviated as DMAC.
If urine is present in the sample, there will be a pink or magenta color on the spot where the urine stain was suspected.
The reaction to occasion that color change indicates the presence of urea, ammonia, or uric acid the usual components of urine. These components are not specific to urine.
They can be found in other body fluids including blood samples. For that reason, after the presumptive test, DNA analysis is the next step and not a confirmatory test for urine.
Saliva Detection Tests
This test confirms the presence of saliva in the sample before DNA analysis can be used to determine to who the saliva belongs especially when there are suspects.
A presumptive test which is mostly an alpha-amylase test is first conducted. As with many presumptive tests, this test will only give an indication of the possibility of saliva in the sample material.
To carry out this presumptive test a reagent that contains amylase (enzyme) is applied to the sample. An appearance of a colored substance around the spot where the sample was, means that amylase has acted upon starch in the sample and indicates that saliva is present.
To confirm this test, there would be a need to perform a specific confirmatory test. Unfortunately, we don’t have many tests available for this step.
This is because this is an area that has perhaps not spurred a lot of interest in the scientific community compared to blood and semen detection research. But with the saliva presumptive test result, you can proceed to do DNA analysis.
Note: It’s important that you note that the body fluids we’ve discussed above are the most used in forensic serology. However, there are many other fluids that are rarely used. Research is also ongoing to identify other targets that could be helpful in forensic serology in the future.
Application of serology results to Resolution of Court Cases
After the results of serology, the next step is the application of those results to the law. When we say finding justice, many people frequently think about punishing the suspects in the case. No, it isn’t about punishing suspects, it is about punishing the right suspects.
Did you know there are so many people who are suspected of committing crimes that they have no idea about? Therefore, forensic serology results can also serve to help in the acquittal or exoneration of innocent suspects.
This way, the police investigators would have to go back to the drawing board if the victim will finally have to get justice. They can carry out more investigations on other suspects until forensic serology and/or DNA analysis identifies who should be punished for the offense.
On the other hand, if the outcome of forensic serology pins the first suspect to the crime scene and shows physical interaction between the suspect and the victim, then the suspect will most likely be indicted.
This will be so, especially if such forensic serology results corroborate other evidence from the police investigation like witness testimonies.
Studying Forensic Science at the University
The study of forensic science includes the study of forensic serology and DNA analysis at the university. There are a few universities in the USA and elsewhere around the world that offer this course.
As already mentioned earlier forensic science is not the only path that you can use to pursue a career in criminal investigations by forensic science.
You may have studied a science course, especially immunology and molecular biology, and be recruited as an investigator.
Conclusion
Forensic serology remains an important branch of criminal investigation even with the advent of DNA analysis the modern way of identifying biological samples.
This method uses antigen-antibody reactions which are immunological techniques in solving criminal justice system problems.
Both criminals and victims can be identified and pinned to the crime scene using this method. Then such evidence is presented in a court of law to help in case determination.
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