Identification and Characterization of Blood and Bloodstains - PowerPoint PPT Presentation

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Identification and Characterization of Blood and Bloodstains

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  1. Identification and Characterization of Blood and Bloodstains

  2. Summary • Introduction to Blood • Identification of Blood as Blood • Determining Species Origin of Blood • Identifying Humans using Blood

  3. Introduction to Blood What you should already know: It’s that red stuff that comes out of your fingers following a kitchen accident.

  4. Introduction to Blood

  5. Introduction to Blood

  6. Introduction to Blood What you should already know: It’s that red stuff that comes out of your fingers following a kitchen accident. Lets look at blood.

  7. Introduction to Blood Red Blood Cells = No DNA White Blood Cells = DNA in nucleus

  8. Introduction to Blood White Blood Cells = DNA in nucleus

  9. Introduction to Blood • RBC = no DNA; WBC = yes DNA • All blood cells have blood groups on outside of cell.

  10. Introduction to Blood ABO blood groups found on outside of cell

  11. Introduction to Blood ABO blood groups found on outside of cell

  12. Introduction to Blood • RBC = no DNA; WBC = yes DNA • All blood cells have blood groups on outside of cell. • Red Blood Cells contain the protein hemoglobin, which carries oxygen

  13. Introduction to Blood Hemoglobin picks up and drops off oxygen

  14. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)

  15. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)

  16. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)

  17. Presumptive Screening Tests • Negative result means the questioned stain is not likely blood • Positive result means the questioned stain is likely blood

  18. Presumptive Screening Tests • Presumptive tests produce a color reaction or release of light • Tests rely on catalytic properties of blood (hemoglobin presence)

  19. Presumptive Screening Tests Color Tests • Apply chromogen (color changing chemical) • Apply oxidizing agent (hydrogen peroxide) • The catalyst of the reaction is hemoglobin Rapid color change is a positive result. This means the stain is blood.

  20. Presumptive Screening Tests Color Test Method • Sample stain with clean cotton swab • Add drop of chromogen • Add drop of hydrogen peroxide

  21. Presumptive Screening Tests Color Test Method • Sample stain with clean cotton swab • Add drop of chromogen • Add drop of hydrogen peroxide • Alternatively, collect stain on thread; add chromogen and hydrogen peroxide in spot plate

  22. Presumptive Screening Tests Color Tests Remember, other non-blood substances might catalyze the reaction also. • Chemical Oxidants • Plant materials False Positive – A positive result given by a substance that is not blood.

  23. Presumptive Screening Tests 5 Types of Color Tests • Benzidine • Phenolphthalein • O-Tolidine • Tetramethylbenzidine (TMB) • Leucomalachite Green (LMG)

  24. Presumptive Screening Tests Benzidine • Positive result = blue color • Carcinogen (cancer causing) in 1974 • No longer used by sane scientists

  25. Presumptive Screening Tests Phenolphthalein • Positive result = pink • Some other substance produce colors other than pink (not blood) • Still used today

  26. Presumptive Screening Tests O-Tolidine • Positive result = blue • Similar to benzidine; still carcinogenic as it can be metabolized to benidine • No longer used; gradually replaced by TMB

  27. Presumptive Screening Tests Tetramethylbenzidine (TMB) • Positive result = Blue-green • Most common test for blood • Rub stain with moist swab • Add TMB • Add peroxidase Look for quick blue color

  28. Presumptive Screening Tests Tetramethylbenzidine (TMB) • Positive result = Blue-green • Most common test for blood • Rub stain with moist swab • Add TMB • Add peroxidase Look for quick blue color

  29. Presumptive Screening Tests Leucomalachite Green (LMG) • Positive result = Green • Not as sensitive as TMB or specific as phenolphthalein

  30. Presumptive Screening Tests Chemiluminescence and Fluorescence • Chemiluminescence – light is emitted as a product of the chemical reation • Fluorescence – light is emitted when a substance is exposed to a shorter wavelength of light

  31. Presumptive Screening Tests Chemiluminescence and Fluorescence • More sensitive than color tests • May damage blood stain (no blood/DNA typing) • Used to locate and define areas of blood • old blood stains • cleaned floor

  32. Presumptive Screening Tests Luminol • Method similar to color test • Luminol is combined with oxidant and sprayed over area thought to contain blood • Emits a blue-white to yellow green glow

  33. Presumptive Screening Tests Luminol

  34. Presumptive Screening Tests Fluorescein • Fluorescein is combined with oxidant and sprayed over area thought to contain blood • Fluoresces when treated with a UV light • Fluorescein includes a thickener; this makes it more effective on vertical surfaces • Study showed no interference with DNA analysis

  35. Presumptive Screening Tests Fluorescein

  36. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)

  37. Confirmatory Tests • Due to the possibility of false positives with the presumptive tests, confirmatory tests are necessary • Confirmatory tests involve making crystals that detect the presence of hemoglobin

  38. Confirmatory Tests Teichmann Test and Takayama Test • Small amount of blood added to microscope slide • Chemical solution is added • Slide is heated to form crystals • Crystals viewed under microscope

  39. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)

  40. Species Origin Most methods test for serum proteins • Serum proteins are found in all animals, but are slightly different • Species ID methods based on antigen/antibody interactions

  41. Species Origin • Antigen = serum protein • Antibody = produced when foreign serum protein is detected • Certain antibody will only attach to one species’ serum protein

  42. Species Origin • Human antiserum will only attach to human blood sample Antibody is in antiserum Antigen(serum protein) is in blood sample • Rabbit antiserum will only attach to rabbit blood sample • Dog antiserum will only attach to dog blood sample

  43. Species Origin Ring Precipitin Test • Blood sample (dilute) in top layer • Antiserum in heavy bottom layer

  44. Species Origin Ring Precipitin Test • Blood sample (dilute) in top layer Precipitate means blood and antiserum species match • Antiserum in heavy bottom layer

  45. Species Origin Ring Precipitin Test Yes line = Yes human blood Human Antiserum

  46. Species Origin Ring Precipitin Test No line = Not human blood Human Antiserum

  47. Species Origin Human blood Ouchterlony Double Diffusion Human antiserum Not human blood • Antiserum placed in center • Several bloodstains tested at one time • White line means antiserum and blood match

  48. Species Origin Crossed-Over Electrophoresis Antiserum Blood Stain Gel Holes • Antiserum and Blood move toward each other

  49. Species Origin Crossed-Over Electrophoresis Antiserum Blood Stain • Antiserum and Blood move toward each other • If line forms, antiserum and blood match

  50. Forensic Analysis of Blood • Visual examination of evidence Presumptive screening test (Is it blood?) Confirmation test (Seriously, is it blood?) Determine species origin (human blood?) Identify the blood (whose blood is it?)