Saliva Examination in Forensic Science

Contents

• Contents
• Abstract
• Introduction
• Advantages of Saliva Examination
• Methods of Detecting Saliva
  1. Chemical Methods
  2. Instrumental Techniques
  3. Recovering Saliva from the Skin
     1. Single Swab Technique
     2. Double Swab Technique
  4. Detection of Drug Abuse through Saliva
• Points to Remember
  1. Rich Source of DNA
  2. Non-invasive Collection
  3. Enzyme-Linked Immunosorbent Assay (ELISA)
  4. Double Swab Technique
  5. Drug Detection
     1. Drug Wipe Technique
     2. Immunoassay Strips
  6. Salivary Biomarkers
  7. DNA Profiling in Bite Marks
  8. Hormone Identification
  9. Toxin and Poison Detection
  10. Mass Disaster Identification
  11. Cytological Analysis
• Conclusion
• Reference

Abstract

This article discusses the role of saliva as a valuable source of DNA for forensic investigations. Saliva offers distinct advantages over blood as a non-invasive, easily collectable, and safer method of obtaining DNA. However, detecting and recovering dried saliva stains from crime scenes can be challenging. The article explores various chemical and instrumental techniques for saliva examination and describes two notable methods for recovering saliva from the skin. Additionally, the article highlights the use of saliva in detecting drug abuse.

Forensic Serology: A Complete Overview

Introduction

The retrieval of minute amounts of bodily fluids stands out as a crucial form of forensic evidence, holding valuable DNA that aids in identifying individuals involved in criminal cases. Among these bodily fluids, saliva, a complex bodily secretion, is pivotal in forensic investigations. Saliva can be left on the skin through actions like biting, sucking, or licking, serving as a noteworthy reservoir of forensic evidence. In recent times, saliva has gained prominence due to its ease of collection, safe handling, and a remarkable similarity to plasma. This has contributed to its growing popularity as a forensic tool, particularly in cases involving crimes, poisonings, animal bites, substance abuse, and hormone identification.

Advantages of Saliva Examination

Saliva offers distinct advantages over blood as a source of DNA for forensic purposes. Firstly, it is a non-invasive method that can be obtained without causing harm or discomfort. Secondly, saliva is easily collectable, eliminating the need for invasive procedures like drawing blood. Thirdly, it is considered safer than blood, as the latter poses a higher risk of contamination, particularly from diseases such as hepatitis and acquired immunodeficiency syndrome (AIDS), which necessitate the use of needles for collection.

Forensic Biology and Forensic Genetics: Analyzing Biological Evidence and DNA for Crime Scene Investigation

Methods of Saliva Examination

Detecting and recovering saliva stains from crime scenes is challenging, mainly because dried saliva stains are invisible to the naked eye. Saliva stains may be found on skin, clothing, paper, or other inanimate objects. Advanced collection methods are required to uncover these imperceptible saliva stains on human skin.

Chemical Methods

Various methods exist for detecting saliva stains. Chemicals and enzymes have been experimented with to identify dried saliva stains. Alkaline phosphatase, starch, and amylase are commonly used enzymes for this purpose, although their application has limitations.

• The alkaline phosphatase test lacks specificity and may yield false-positive results.
• The iodine or starch test for detecting salivary amylase enzyme can give a negative reaction, leading to false positives when excess starch is present.
• Nitrate and thiocyanate salts have also been employed, but the drawback is that this method only applies to samples up to 2 days old.

Instrumental Techniques

Several techniques, such as lasers, ultraviolet light, and quartz arch tubes, are screening methods for identifying dried saliva stains.

Fluorescence spectroscopy, a widely used technique for analyzing protein structure and interactions, involves exciting a fluorescent material with radiation of a specific wavelength.

Salivary amylase, containing the aromatic amino acid tryptophan, emits unique radiation when excited with 282 nm wavelength radiation, allowing for sensitive identification of dried saliva stains on the skin.

Recovering Saliva from the Skin

Retrieving salivary evidence is crucial for identity testing, particularly when only minute amounts of saliva are deposited on the skin, often associated with bite marks. Employing proper collection methods becomes essential to maximize the recovery of cells in the saliva while minimizing potential contamination from the victim’s skin. When exposed to air, saliva undergoes drying, causing the desiccation of most desquamated epithelial cells and leukocytes in the saliva.

Various techniques are employed to recover saliva from the skin, with two notable methods described below:

Single Swab Technique

This classical method uses a wet cotton swab or wet filter paper to collect saliva traces from the skin.

Double Swab Technique

This advanced technique requires two sterile cotton swabs and 3 mL of sterile, distilled water.

Procedure:

• Soak the first cotton swab in sterile, distilled water.
• Roll the wet swab over the suspected area with slight pressure in a circular motion.
• Allow the first swab to dry in a contamination-free environment for at least 30 minutes.
• Within 10 seconds after the first swab, roll the second dry swab across the now moist area.
• Apply moderate pressure to absorb the wetness into the second swab.
• Allow the second swab to dry for a minimum of 30 minutes in a contamination-free environment.
• After drying, pack and seal both swabs together, marking them with sample and case numbers.

A study by Sweet et al. revealed that the double swab technique is more effective in yielding saliva from the skin surface. This superiority may be attributed to the moisture from the first swab rehydrating and loosening the majority of dried epithelial cells within the saliva, which then adhere to the fibres in the cotton swab. When the second (dry) swab is applied, the rehydrated cells adhere more easily to the fibres, allowing for the collection of a larger amount of DNA samples compared to the classical method.

Detection of Drug Abuse through Saliva

The concentration of a specific drug in saliva is often directly linked to its concentration in the bloodstream. Drugs enter saliva through a process known as simple diffusion. The drug wipe technique is a method employed to assess the presence of drugs in saliva.

Introduction To Drug Classes

Points to Remember

Here are some key facts that forensic students should remember about the saliva examination in forensic science:

Rich Source of DNA

Saliva is a valuable source of DNA, containing epithelial cells and leukocytes that can be used for DNA profiling in forensic investigations.

Non-invasive Collection

Saliva collection is non-invasive, making it more acceptable and less discomforting for individuals than other bodily fluids like blood.

Enzyme-Linked Immunosorbent Assay (ELISA)

ELISA techniques using monoclonal antibodies targeting salivary immunoglobulin A are employed for species identification in animal bite mark analysis.

Double Swab Technique

The double swab technique is effective for recovering saliva from skin surfaces, offering improved DNA sample collection compared to the classical single swab method.

Drug Detection

Saliva is used for drug detection, and the drug wipe technique is employed for wiping surfaces to recover traces of drug residue, providing insights into recent drug use.

Drug Wipe Technique

• Drug Wipe is a test designed to recover traces of drug residue by wiping surfaces.
• It is versatile and applicable to both sweat and saliva for testing individuals.
• The test involves wiping a small, wet fleece on the suspected site.
• It can detect the presence of various drugs, including cannabis, cocaine, crack cocaine, heroin, morphine, and benzodiazepines.

Immunoassay Strips

Immunoassay strips are utilized in the Drug Wipe technique and contain antibodies that bind to specific components of a drug.

Studies have demonstrated the effectiveness of detecting drugs like amphetamine, phenobarbital, and morphine in saliva using radioimmunoassay.

Salivary Biomarkers

Salivary biomarkers are utilized for general identification in bite mark cases and victim identification in mass disaster scenarios. These biomarkers can be associated with specific diseases or conditions.

DNA Profiling in Bite Marks

DNA profiling from saliva is instrumental in bite mark analysis, aiding in identifying individuals involved in biting incidents.

Hormone Identification

Saliva is used for hormone identification, helping assess stress levels and other physiological conditions by analysing cortisol and other hormonal markers.

Toxin and Poison Detection

Saliva examination can assist in detecting toxins and poisons ingested by individuals, providing critical forensic evidence in cases of suspected poisoning.

Mass Disaster Identification

Saliva plays a vital role in human identification in mass disaster scenarios, where traditional identification methods may be challenging or impractical.

Cytological Analysis

Cytological analysis of saliva is utilized for sex determination, aiding forensic investigations in cases where the suspect’s identity needs to be established.

Conclusion

In conclusion, saliva analysis offers a promising avenue for forensic investigations, particularly in cases involving crimes, poisonings, animal bites, substance abuse, and hormone identification. Saliva’s non-invasive, easily collectable, and safer method of obtaining DNA makes it a valuable source of evidence. However, detecting and recovering saliva stains from crime scenes is a challenging task, requiring advanced collection methods. Nonetheless, advancements in instrumental techniques like fluorescence spectroscopy have made it possible to identify dried saliva stains accurately. Proper collection methods, like the double swab technique, have also been shown to maximize the recovery of cells in the saliva while minimizing potential contamination from the victim’s skin. Overall, saliva analysis offers great potential in forensic investigations, and further research in this field can lead to even more breakthroughs. 

Reference

• Virkler K, Lednev IK. Analysis of body fluids for forensic purposes: from laboratory testing to non-destructive rapid confirmatory identification at a crime scene. Forensic Sci Int 2009 Jul;188(1-3):1-17.
• Saxena S, Kumar S. Saliva in forensic odontology: a comprehensive update. J Oral Maxillofac Pathol 2015 May-Aug; 19(2):263-265.
• Mago J, Sidhu L, Kaur R, Kamal, Anurag T. Saliva in forensics. World J Pharm Med Res 2016;2(4):196-198.
• Nanda KD, Ranganathan K, Umadevi K, Joshua E. A rapid and noninvasive method to detect dried saliva stains from human skin using fluorescent spectroscopy. J Oral Maxillofac Pathol 2011 Jan;15(1):22-25.
• Sweet D, Lorente M, Lorente JA, Valenzuela A, Villanueva E. An improved method to recover saliva from human skin: the double swab technique. J Forensic Sci 1997 Mar;42(2): 320-322.
• Stimson, PG.; Mertz, CA. Forensic dentistry. Boca Raton (FL): CRC Press, LLC.; 1997.
• Kramvis A, Bukofzer S, Kew MC. Comparison of hepatitis B virus DNA extractions from serum by the QIAamp blood kit, GeneReleaser, and the phenol-chloroform method. J Clin Microbiol 1996 Nov;34(11):2731-2733.
• Aps JK, Martens LC. Review: the physiology of saliva and transfer of drugs into saliva. Forensic Sci Int 2005 Jun;150(2-3):119-131.
• Gentili S, Solimini R, Tittarelli R, Mannocchi G, Busardò FP. A study on the reliability of an on-site oral fluid drug test in a recreational context. J Anal Methods Chem 2016 Aug; 2016:1234581.
• Fletcher SM, Dolton P, Harris-Smith PW. Species identification of blood and saliva stains by enzyme-linked immunoassay (ELISA) using the monoclonal antibody. J Forensic Sci 1984;29:67-74.