1 / 15

Forensic Biology by Richard Li

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

zahi
Download Presentation

Forensic Biology by Richard Li

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 6: Identification of Blood Forensic Biologyby Richard Li

  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. Hemoglobin: Transports oxygen from lungs to body tissues; helps with transport of CO2 out of the tissues and back to the lungs Heme: Prosthetic group in hemoglobin; Binds oxygen; also has peroxidase activity

  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. 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) Emits (fluoresces) light here Absorbs light here

  12. 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

  13. Positive Takayama confirmatory test for blood

  14. 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

More Related