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Forensic Biology by Richard Li

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Chapter 6: Identification of Blood * Normal blood volume is 8% of body weight = 5-8 pints for average adults Fatal if lose 40% or more of blood volume Two portions ... – PowerPoint PPT presentation

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Title: Forensic Biology by Richard Li


1
Forensic Biologyby Richard Li
  • Chapter 6 Identification of Blood

2
Biological Properties of Blood
  • Normal blood volume is 8 of body weight
  • 5-8 pints for average adults
  • Fatal if lose 40 or more of blood volume
  • Two portions
  • Fluid portion
  • Plasma- fluid portion of blood that can clot
  • Serum- remaining fluid after clot is removed
  • Cellular Portion
  • Red blood cells (erythrocytes hemoglobin No
    DNA)
  • White blood cells (Leucocytes fight infection
    DNA present)
  • Platelets (Thrombocytes blood clotting No DNA)

3
Plasma and serum
4
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5
Two Types of Assays
  • Presumptive
  • Very sensitive, fast, and easy to perform
  • Depend on oxidation-reduction reaction catalyzed
    by heme group of blood
  • Result in color change or release of photon by
    chemiluminescence or fluorescence
  • Confirmatory
  • Need a lab to perform greater specificity
  • Depend on crystal formation, primary serological
    reactions, spectrophotometry, or RNA-based assays

6
Presumptive Assays
  • Detect traces of blood
  • Oxidation-reduction reaction catalyzed by heme
  • Oxidation- lose electron
  • Hydrogen peroxide used as an oxidant
  • E.g. K-M test described in Lecture 5
  • Reduction- gain electron
  • Tests result in
  • Change of color (colorimetric assays)
  • Release of photons
  • Chemiluminescence or fluorescence

7
Presumptive Assays
  • Colorimetric Assays
  • Phenolphthalein (Kastle-Meyer)
  • -Introduced in Lecture 5
  • We will perform this test in lab
  • Leucomalachite green (LMG)
  • Colorless in reduced state green when oxidized
  • Benzadine and Derivatives
  • Benzadine colorless in reduced state dark blue
    when oxidized
  • Tetramethylbenzidine (TMB) colorless in reduced
    state blue-green when oxidized

8
Presumptive Assays
  • Chemiluminescent assays
  • Light is emitted as a product of the chemical
    reaction
  • Luminol- emits light blue color
  • Useful when blood has been cleaned up
  • Performed in darkness
  • Can detect small traces of blood
  • Can detect patterns
  • May dilute sample

9
Presumptive Assays
  • False positive results with luminol
  • Bleach
  • Plants
  • Copper and copper-containing alloys
  • Feces
  • Urine (if blood is present, including menstrual
    blood)

10
Presumptive Assays
  • Fluorescence assays
  • Absorption of UV or visible radiation kicks
    electrons up to a higher orbitial (higher energy
    state)
  • When electrons drop down to original ground
    state
  • Energy released is transferred to vibrational and
    rotational energy of molecular bonds (most
    common)
  • Energy released as a photon of lower energy
    wavelength (less common) fluorescence

11
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12
Presumptive Assays
  • Fluorescin
  • When oxidized by the peroxidase activity of heme
    in the presence of hydrogen peroxide, will
    fluoresce
  • Must be exposed to wavelength 425-485 nm
    (blue-purple) from an ALS
  • Emits yellowish-green color (longer wavelength)

13
Confirmatory Assays
  • Microcrystal assays
  • Hemochromagen crystal assay (Takayama)
  • Hematin crystal assay (Teichmann)
  • Method
  • Small amount of putative blood added to a slide
  • Chemical solution added
  • Slide heated to form crystals (if blood present)
  • Crystals viewed under the microscope

14
Positive Takayama confirmatory test for blood
15
Confirmatory Assays
  • Other
  • Chromatographic and electrophoretic methods
  • Identify human hemoglobin based on mobility on
    columns or in gels
  • Spectrophotometric methods
  • Identify human hemoglobin based on light spectra
    absorbed by hemoglobin and its derivatives
  • Immunological methods
  • Anti-human hemoglobin antibodies (see Lecture 5)
  • RNA-based methods
  • Assay for presence of mRNAs found only in human
    blood
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