Identification and Characterization of Blood and Bloodstains Summary

Identification and Characterization of Blood and Bloodstains

Summary n Introduction to Blood n Identification of Blood as Blood n Determining Species Origin of Blood n Identifying Humans using Blood

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.

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

Introduction to Blood ABO blood groups found on outside of cell

Red blood cells contain hemoglobin Hemoglobin picks up and drops off oxygen

Forensic Analysis of Blood 1. Visual examination of evidence 2. Presumptive screening test (Is it blood? ) Confirmation test (Seriously, is it 3. 4. 5. blood? ) Determine species origin (human blood? ) Identify the blood (whose blood is it? )

Presumptive Screening Tests Negative result means the questioned stain is not likely blood n Positive result means the questioned stain is likely blood n

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

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.

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

Presumptive Screening Tests Benzidine n Positive result = blue color n Carcinogen (cancer causing) in 1974 n No longer used by most scientists

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

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

Presumptive Screening Tests Tetramethylbenzidine (TMB) n Positive result = Blue-green n Most common test for blood 1. Rub stain with moist swab 2. Add TMB 3. Add peroxidase Look for quick blue color

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

Presumptive Screening Tests Chemiluminescence and Fluorescence n Chemiluminescence – light is emitted as a product of the chemical reation n Fluorescence – light is emitted when a substance is exposed to a UV light

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

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

Presumptive Screening Tests Luminol

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

Presumptive Screening Tests Fluorescein

Forensic Analysis of Blood 1. Visual examination of evidence 2. Presumptive screening test (Is it blood? ) Confirmation test (Seriously, is it 3. 4. 5. blood? ) Determine species origin (human blood? ) Identify the blood (whose blood is it? )

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

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

Forensic Analysis of Blood 1. Visual examination of evidence 2. Presumptive screening test (Is it blood? ) Confirmation test (Seriously, is it 3. 4. 5. blood? ) Determine species origin (human blood? ) Identify the blood (whose blood is it? )

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

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

Forensic Analysis of Blood 1. Visual examination of evidence 2. Presumptive screening test (Is it blood? ) Confirmation test (Seriously, is it 3. 4. 5. blood? ) Determine species origin (human blood? ) Identify the blood (whose blood is it? )

Genetic Markers in Blood If a stain is blood, and it is human blood, then whose is it? n Blood Group Markers n Protein/Enzyme Markers n DNA