FRSC 202 Serology
Sarah Williams・29 minutes read
Forensic biology involves identifying body fluids and DNA in crime labs, with serology and DNA analysis being crucial components. Confirmatory tests for blood and semen, as well as species identification and saliva testing, are vital in forensic analysis, but challenges remain in differentiating fluids like menstrual blood for justice purposes.
Insights
- Serology and DNA analysis are crucial components of forensic biology, focusing on identifying biological materials related to crimes and determining genetic profiles. Serology, despite being developed in the 1930s, remains essential in criminal cases, especially for verifying sexual assault through semen presence, making it a time-consuming but vital part of forensic analysis.
- Confirmatory tests, such as those using phenolphthalein, tetramethylbenzidine, or specialized cards like the Hematrace card, are employed in forensic labs to confirm the presence of blood or semen, providing species specificity and aiding in absolute confirmation of biological samples. However, challenges persist in differentiating menstrual blood from other sources, necessitating ongoing research to enhance identification methods for these fluids in the future.
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Recent questions
What is the primary focus of forensic biology?
Identification of body fluids and DNA analysis.
What are the specialized areas within forensic biology?
Forensic entomology and microbiology.
How does serology contribute to forensic analysis?
By detecting biological materials related to crimes.
What techniques are used to enhance blood visibility in forensic analysis?
Luminol and fluorescein.
How are confirmatory tests for blood conducted in forensic laboratories?
Using phenolphthalein, tetramethylbenzidine, or Hematrace card.
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Summary
00:00
Forensic Biology: Key Components and Techniques
- Forensic biology encompasses body fluid identification and DNA analysis, with serology and DNA being key components in crime laboratories.
- Other areas like forensic entomology and microbiology are specialized and typically found in university systems or federal wildlife forensic labs.
- Various evidence types, from boats to food and firearms, are analyzed in forensic biology units for body fluids linked to crimes.
- Workflow in a forensic biology unit involves locating stains, collecting and preserving them, conducting tests to detect body fluids, identifying human or non-human origin, and determining genetic profiles.
- Serology focuses on detecting biological materials related to crimes, using tests developed in the 1930s and still crucial despite DNA advancements.
- Blood analysis involves identifying stains, conducting presumptive or confirmatory tests, and using enhancement techniques like luminol and fluorescein for invisible stains.
- Luminol and Blue Star enhance blood visibility in dark or cleaned surfaces through chemiluminescent reactions, emitting blue light where blood is present.
- Fluorescein, activated by blood reacting with hydrogen peroxide, undergoes a chemical change to fluorescein, aiding in blood detection.
- Serology remains vital in criminal cases, especially for verifying sexual assault through semen presence, and is the most time-consuming part of forensic analysis.
- Evidence analysis involves locating stains visually, conducting presumptive tests, and using enhancements like luminol and fluorescein for invisible blood stains.
19:33
Detecting Biological Evidence in Forensic Investigations
- Yellow fluorescence stains are fluorescein-based due to the presence of blood, but visible blood can quench the fluorescence, potentially leading to false positives.
- To confirm the presence of blood after locating a stain, laboratories often use phenolphthalein, tetramethylbenzidine, or a combination of both, which change color in the presence of blood due to iron's peroxidase-like activity.
- Confirmatory tests for blood, like the Hematrace card by Abacus Diagnostics, are specific for human blood, similar to a pregnancy test but detecting human hemoglobin instead of HCG.
- Semen is primarily composed of liquid seminal plasma, essential for sperm survival, and cellular components, including sperm cells and occasionally epithelial cells and white blood cells.
- To detect dried semen, alternate light sources like ultraviolet or blue light can make it fluoresce, aiding in identification on evidence.
- Acid phosphatase tests are used to detect the enzyme present in semen, with a color change indicating its presence, but false positives and negatives can occur.
- Microscopic identification of sperm cells is a confirmatory test for semen, as sperm cells are only found in the testes and semen, providing absolute confirmation.
- Immunochromatographic cards, like those testing for the P30 protein, are commonly used for confirmatory tests for semen, especially in cases where sperm cells may not be present.
- Species identification tests, like octalone double diffusion or DNA analysis, can determine the source of biological samples, providing species specificity.
- Saliva testing, often done using starch iodine or fatibus tests, can detect the presence of amylase enzyme in saliva, with color changes indicating its presence, though it's not commonly tested for in forensic labs.
39:27
Challenges in Identifying Body Fluids for Justice
- Vomit, CSF, breast milk, and amniotic fluid can be identified by a pathologist based on cellular characteristics, while tears and nasal secretions are more challenging to identify. Vaginal and menstrual secretions can be identified using messenger RNA or other molecular methods, but the US has not accepted these methods for casework due to technical and patent issues.
- The US has not approved messenger RNA analysis for identifying body fluids like brain, lung, and gut fluids, unlike Europe, New Zealand, and Australia. Current methods struggle to differentiate menstrual blood from other sources, leading to challenges in cases like sexual assault where proving the origin of blood is crucial for justice. Researchers are actively working to improve identification methods for these fluids over the next decades.
