Forensic Biology by Richard Li

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Forensic Biologyby Richard Li

• Chapter 9 Identification of Saliva and Other
  Biological Fluids

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Saliva Biological Characteristics

• Human salivary glands produce 1.0-1.5 liters per
  day
• Mostly water
• Amylase- digests starch in the oral cavity and
  small intestine
• Two types of amylase
• ß-amylase Plant and bacterial sources
• a-amylase HSA (human saliva), HPA (human
  pancreas)

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Saliva Presumptive Assays

• Visual Examination
• ALS (470nm), Microscopic
• Starch-iodine assays
• Iodine used to test for starch
• Not specific
• Colorimetric assays
• Dye-labeled amylase substrates are employed
• Phadebas test

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Saliva Presumptive Assays

• Starch-iodine assays
• Amylase overlay assay already discussed
• Well perform this assay in lab
• Amylase radial diffusion assay
• Pour agar gel containing starch into culture
  plate
• Create wells in solidified agar with vacuum punch
• Add extract of evidence sample to well Add
  standards to other wells (amylase samples at
  known concentrations)
• Incubate overnight at 37 degrees C
• Stain with iodine solution

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Saliva Presumptive Assays

• Phadebas tablets consist of insoluble starch
  polymers to which a blue dye has been covalently
  bound
• Extract sample and add tablet
• When amylase is present
• Polymers are degraded
• Dye is liberated and becomes soluble
• Concentration of soluble dye is measured by
  spectrophotometry at 620 nm

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Saliva Confirmatory Assays

• Immunochromatographic Assays
• RSID-Saliva
• Similar to PSA and hemoglobin tests
• ELISA
• Monoclonal HSA antibody
• RNA-based assays
• Certain genes are specifically expressed in
  certain types of cells
• Amylase mRNA

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Misc. Biological Fluids

• Vaginal secretions, Menstrual blood, Urine,
  Vomitus, and Feces
• Less frequently encountered
• Can be probative in certain cases
• Vaginal secretions
• Gel mobility assays
• Compare SAP and VAP mobilities in protein gel
• RNA-based assays
• ß-defensin 1 antimicrobial peptide
• Mucin 4 (membrane protein of endocervix)

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Misc. Biological Fluids

• Menstrual Blood
• Color assays
• Detect glycogenated nucleated squameous
  epithelial cells in vaginal secretions
• Can also be used to test for vaginal secretions
• RNA assay
• Detects matrix metalloprotease, found only in
  menstrual blood
• Involved in tissue remodeling during menstruation

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Misc. Biological Fluids

• Urine
• Presumptive assay tests for urea
• All animals must get rid of excess nitrogen from
  breakdown of proteins and amino acids
• Aquatic animals get rid of nitrogen as ammonia
• Birds and terrestrial reptiles use uric acid
• Mammals use urea and expel in urine

Urea
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Misc. Biological Fluids

• Assay for urea
• Prepare Whatman filter paper circle with one drop
  of bromothymol blue, a pH indicator dye
• Yellow-green at pH 6
• Aqua blue at ph greater than 7.6
• Allow bromothymol blue to dry
• Add drop of extract from evidence sample on top
  of dye, then add drop of urease
• If urea present, urease will degrade to ammonia
• Ammonia will raise pH and dye will turn aqua blue

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Misc. Biological Fluids
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Misc. Biological Fluids

• Confirmatory tests for human urine
• Immunological assays
• ELISA or immunochromatographic test for presence
  of Tamm Horsefall glycoprotein
• Abundant in urine
• Human form can be targeted
• Ouchterlony assay
• Less sensitive
• Based on precipitation reaction between antibody
  and antigen (human Tamm Horsefal proteinl) in
  diffusion gels

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Misc. Biological Fluids

• Vomitus
• Microscopy for food particles
• Enzymatic test for pepsin
• Proteolytic enzyme secreted from gastric gland
• Sweat
• Immunological assays
• Human sweat-specific antigen

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Misc. Biological Fluids

• Feces
• During heme catabolism, waste product called
  bilirubin is produced
• Bilirubin excreted in feces gives it its brown
  color
• Gut bacteria break down some of bilirubin to
  urobilinogen, which is also excreted in feces

Urobilinogen
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Misc. Biological Fluids

• Presumptive Assay for Feces
• Prepare extract of feces stain
• Oxidize to urobilinogen to urobilin
• Add zinc chloride
• If urobilin present, extract will fluoresce under
  UV light
• Confirmatory Assay for Feces
• Microscopy to look for animal and plant cells
  present due to digestion

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