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| Saliva and it's Forensic Examinations |
What is Saliva?
Saliva is a predominantly watery fluid that contains small quantities of electrolytes and enzymes. It is produced by a pair of salivary glands located in the mouth. One of the key components of saliva is the enzyme alpha-amylase, which is also referred to as α-amylase, salivary amylase, or Ptyalin. This enzyme plays a crucial role in breaking down complex carbohydrates into smaller sugar molecules.
In the field of forensics, saliva frequently serves as a valuable piece of evidence in sexual assault cases. Through saliva tests, it becomes possible to identify specific disease markers, detect viral infections, and determine the presence of both therapeutic and illicit drugs in an individual's system. Saliva samples can be collected and examined from a variety of surfaces, including body parts, paper, envelopes, cigarette butts, plastic and glass bottles, and metal cans, among others. These samples provide important information for forensic investigations.
Examination of Saliva:
Saliva serves as a valuable source of evidence that can provide significant insights into the personal interaction between a victim and a perpetrator. The presence of saliva can be determined through tests such as the Starch-iodide and Phadebas tests. However, it is important to note that these tests do not specifically confirm the presence of human saliva. Instead, they assess the activity of amylase, irrespective of whether it originated from a human or another source.
To accurately identify human-specific salivary amylase, an advanced test kit utilizing monoclonal antibodies is utilized. The RSID method, in particular, is employed to detect the presence of human saliva. If a stain produces a positive reaction using this method, it can be confirmed that human saliva is indeed present.
Furthermore, ABO group antigens can also be detected in saliva, but only if the individual is a secretor. Secretors are individuals whose saliva and other bodily fluids contain ABO antigens. It is worth noting that approximately 80% of individuals are known to be secretors.
Different Tests for Saliva:
- Starch-iodide test
- Phadebas Reagent
- RSID (Rapid Stain Identification) Test
- ABO Group Identification
- DNA Identification
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| Different Forensic Tests For Saliva |
1. Starch Iodide Test:
The Starch Iodide Test is a chemical test used to detect the presence of amylase, an enzyme found in saliva that helps break down starches into simpler sugars. Here is a brief description of the test and some references to provide further context:
Test Procedure:
a. Prepare a starch solution by dissolving starch in water.
b. Take a small amount of saliva and add it to the starch solution.
c. Add a few drops of iodine solution to the mixture.
d. Observe the color change:
- If the starch is not broken down, the mixture will turn blue-black due to the iodine-starch complex.
- If the starch is partially broken down, the mixture will show a brownish color.
- If the starch is completely broken down, the mixture will remain yellowish-brown, indicating the absence of starch.
References:
a. Biochemistry by Jeremy M. Berg, John L. Tymoczko, and Gregory J. Gatto Jr. (9th edition) - Chapter 6: Enzymes, page 170.
b. Principles and Techniques of Practical Biochemistry by Keith Wilson and John Walker (6th edition) - Chapter 4: Enzymes, page 95.
c. Lehninger Principles of Biochemistry by David L. Nelson and Michael M. Cox (7th edition) - Chapter 8: Enzymes: Basic Concepts and Kinetics, page 246.
2. The Phadebas reagent test:
The Phadebas reagent test for saliva is a forensic tool used to detect the presence of human saliva on various surfaces. It is based on the specific reaction between a glycoprotein present in saliva called alpha-amylase and the Phadebas reagent.
The Phadebas reagent is a chemical solution containing blue dye particles that are coated with starch. When saliva comes into contact with the Phadebas reagent, the alpha-amylase enzyme in saliva breaks down the starch into smaller fragments. This enzymatic reaction leads to a color change in the reagent from blue to a distinct shade of purple.
To conduct the Phadebas reagent test, a small sample from the suspected surface is collected using a cotton swab or a piece of filter paper. The collected sample is then treated with the Phadebas reagent solution. If human saliva is present on the surface, the reagent will undergo a color change, indicating a positive result. On the other hand, if there is no color change, it suggests the absence of human saliva.
The Phadebas reagent test is commonly employed in forensic investigations to identify saliva stains at crime scenes. It can be particularly useful in cases involving assaults, sexual offenses, or when identifying potential sources of DNA for further analysis.
References:
1. Bremmer, R. H., Beerkens, J. G., Damen, J. M., Koeman, J. H., & Oosterbaan, A. F. (1988). Identification of saliva stains: A comparison of different methods. Journal of Forensic Sciences, 33(3), 726-733.
2. Sankaranarayanan, H. S., Neelakantan, S., Sanghvi, Y. S., & Natarajan, K. S. (1991). New approach for the identification of saliva stains. Journal of Forensic Sciences, 36(2), 454-457.
3. RSID (Rapid Stain Identification) Test:
The RSID (Rapid Stain Identification) test is a forensic tool used for the rapid detection and identification of biological fluids, such as saliva, at crime scenes. It is designed to provide quick and reliable results, allowing investigators to gather valuable information in a timely manner.
The RSID test for saliva works by detecting specific proteins and enzymes that are unique to saliva. It utilizes immunochromatographic technology, similar to a pregnancy test, to generate a visual result. When a sample containing saliva is applied to the test, the proteins or enzymes in the saliva bind to specific antibodies on the test strip, causing a visible line to appear. The presence of the line indicates a positive result for saliva.
The RSID test for saliva has proven to be a valuable tool in forensic investigations, allowing investigators to quickly confirm the presence of saliva at crime scenes. This information can help link suspects to the scene or provide additional evidence for further analysis.
References:
1. Schwartz TR, Clark SM, Pillai RK, Garvey S, Montgomery AH, Rieders F, et al. Validation of a rapid stain identification (RSID) test for the detection of saliva and semen. J Forensic Sci. 2013 Jul;58(4):859-67. doi: 10.1111/1556-4029.12128. PMID: 23586553.
2. Griffiths P, James H, Moffatt C. Evaluation of the RSID™-Saliva kit for the detection of human salivary α-amylase. Forensic Sci Int Genet. 2015 Sep;19:144-9. doi: 10.1016/j.fsigen.2015.07.006. Epub 2015 Jul 28. PMID: 26282740.
4. ABO Group Identification:
ABO group identification refers to the determination of an individual's blood type based on the presence or absence of specific antigens on the surface of red blood cells. While blood typing is typically performed using blood samples, advancements in technology have enabled the identification of ABO groups using saliva samples as well.
The ABO blood group system classifies blood into four main types: A, B, AB, and O. These blood types are determined by the presence or absence of antigens A and B on the surface of red blood cells. Additionally, individuals may have antibodies in their plasma against the antigens they do not possess.
Saliva contains a small amount of blood group substances, including ABO antigens and antibodies, derived from oral mucosa cells and gingival crevicular fluid. Researchers have explored the use of saliva as a non-invasive and convenient alternative to blood for ABO group identification. Various studies have demonstrated the feasibility and accuracy of saliva-based ABO typing methods.
One common technique for ABO group identification in saliva is the saliva agglutination test. In this method, saliva samples are mixed with known anti-A and anti-B reagents. If agglutination occurs when mixed with anti-A, the individual is classified as blood group A. Similarly, if agglutination occurs with anti-B, the individual is classified as blood group B. If agglutination occurs with both anti-A and anti-B, the individual is classified as blood group AB. If no agglutination occurs with either reagent, the individual is classified as blood group O.
It's worth noting that saliva-based ABO group identification may have some limitations compared to traditional blood typing methods. The concentration of ABO substances in saliva is lower than in blood, which can affect the sensitivity and accuracy of the tests. Additionally, certain factors like recent blood transfusions or heavy smoking may affect the reliability of saliva-based ABO typing results.
References:
1. Hong JH, et al. (2018). ABO genotyping using the saliva sample. Annals of Laboratory Medicine, 38(1), 67-70. doi: 10.3343/alm.2018.38.1.67
2. Patidar GK, et al. (2015). Saliva: A non-invasive tool for ABO blood grouping in relation to gender. Journal of Forensic Dental Sciences, 7(3), 227-231. doi: 10.4103/0975-1475.172457
3. Rahim S, et al. (2020). Saliva as an alternative to blood for ABO genotyping: A systematic review and meta-analysis. International Journal of Molecular Sciences, 21(18), 6631. doi: 10.3390/ijms21186631
5. DNA Identification :
DNA identification in saliva is a widely used method in forensic science and genetic testing. Saliva contains cells from the oral cavity, which can provide valuable genetic information for identification purposes. DNA profiling from saliva samples has proven to be an effective and non-invasive method for identifying individuals and establishing biological relationships.
The process of DNA identification from saliva typically involves the following steps:
1. Collection of Saliva Sample: Saliva samples can be collected using various methods, including swabbing the inside of the cheek or using specialized collection devices such as saliva collection kits. These methods ensure the collection of an adequate amount of DNA-containing cells.
2. DNA Extraction: Once the saliva sample is collected, DNA extraction is performed to isolate the DNA from other cellular components. This can be achieved using various extraction techniques, such as organic extraction or commercial DNA extraction kits specifically designed for saliva samples.
3. DNA Quantification: After extraction, the concentration and purity of the extracted DNA are determined using spectrophotometry or fluorometry. This step helps ensure that the DNA sample has sufficient quantity and quality for subsequent analysis.
4. DNA Profiling: The extracted DNA is then subjected to DNA profiling techniques, such as polymerase chain reaction (PCR) and short tandem repeat (STR) analysis. PCR amplifies specific regions of the DNA, while STR analysis examines genetic markers that vary between individuals.
5. Data Analysis: The DNA profile obtained from the saliva sample is compared to known DNA profiles in databases to identify potential matches or establish relationships. Advanced statistical algorithms and software are used to analyze the data and determine the likelihood of a match.
It's important to note that the accuracy and reliability of DNA identification from saliva samples depend on various factors, including sample collection techniques, DNA extraction methods, and laboratory procedures. Proper handling and storage of saliva samples are crucial to ensure the preservation of DNA integrity.
References:
1. Budowle, B., Moretti, T. R., & Baumstark, A. L. (1999). Definitive identification of saliva by DNA analysis. Annals of the New York Academy of Sciences, 884(1), 199-212.
2. Prinz, M., Carracedo, Á., Mayr, W. R., Morling, N., Parsons, T. J., Sajantila, A., ... & Schneider, P. M. (2007). DNA Commission of the International Society of Forensic Genetics (ISFG): Recommendations regarding the role of forensic genetics for disaster victim identification (DVI). Forensic Science International: Genetics, 1(1), 3-12.
3. Sweet, D., Lorente, M., Lorente, J. A., Valenzuela, A., Villanueva, E., & Lorente, M. (1997). An improved method to recover saliva from human skin: the double swab technique. Journal of Forensic Sciences, 42(2), 320-322.
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