Forensic Biology by Richard Li Chapter 6: Identification of Blood Forensic Biology by Richard Li

Identification of Blood Preliminary Assays Positive result indicates the possibility of the presence of blood Not specific only for blood Quick, easy, sensitive Not human specific Screening tool Confirmatory Assays Rarely performed…analyzed for DNA Forensic Biology by Richard Li

Biological Properties of Blood Normal blood volume is 8% of the body weight Plasma- fluid portion of blood and can clot Serum- remaining fluid after clot is removed Cellular Portion Red blood cells (erythrocytes) (No DNA) Hemoglobin- transports oxygen Heme molecule White blood cells (Leucocytes) (DNA present) Platelets (Thrombocytes) (No DNA) Forensic Biology by Richard Li

Presumptive Assays Detect traces of blood Oxidation-reduction reaction catalyzed by heme Oxidation- lose electron Hydrogen peroxide used as an oxident Reduction- gain electron Results is a change of color, chemiluminescence, or fluorescence Forensic Biology by Richard Li

Presumptive Assays Colorimetric Assays Phenolphthalein Leucomalachite green (LMG) Ortho-Tolidine Tetramethylbenzidine (TMB) Forensic Biology by Richard Li

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 Forensic Biology by Richard Li

Presumptive Assays Fluorescence assays Fluorescin Must be exposed to a particular wavelength of light 425-485 nm from ALS Emits yellowish-green color Forensic Biology by Richard Li

Presumptive Assays Factors Affecting Presumptive Assay Results Oxidizing agents Cause false positives Metal salts, bleach, household cleaners Plant peroxidases False positives Horseradish Reductants False negative Forensic Biology by Richard Li

Confirmatory Assays Microcrystal assays Other Hemochromagen crystal assay Hematin crystal assay Other Chromatographic methods Electrophoreic method Spectrophotometric methods Immunological methods Forensic Biology by Richard Li