Chapter 12: Identification of Biological Evidence

Blood

constitutes about 8% of the human body weight of a healthy individual.

Plasma

The fluid portion of the blood.

Red Blood Cells

Also known as **erythrocytes**. Their life span in humans is approximately 3–4 months.

Red Blood Cells

They do not have nuclei, and therefore lack nuclear DNA.

hemoglobin

proteins that are responsible for the transportation of oxygen.

Ferroprotoporphyrin

A heme molecule.

White Blood Cells

Also called **leucocyte**s. They are involved in defending the body against infection. They have nuclei and thus represent the main sources of nuclear DNA from the blood.

Platelets

Also known as **thrombocytes**. Like erythrocytes, they lack nuclei.

Platelets

They play a role in blood clotting. They aggregate at sites of vascular and blood vessel injury.

Presumptive blood assays

are designed to detect traces of blood.

Oxidation–Reduction Reactions

These involves a change in the oxidation state of a molecule.

Oxidants

Chemicals that can be reduced and gain electrons from other molecules.

Reductants

Chemicals that can be oxidized and therefore lose electrons to other molecules.

Phenolphthalin Assay

It presents the results of a reaction in which phenolphthalin, a colorless compound, is catalyzed by heme with hydrogen peroxide as the oxidant.

Phenolphthalein

A member of a class of indicators and dyes, is used in titrations of mineral and organic acids as well as most alkalis.

Benzidine

Used a presumptive assay for the presence of blood after the discovery that the oxidation of benzidine can be catalyzed by heme to produce a blue to dark blue color.

Orthotolidine

A dimethyl derivative of benzidine. Its oxidation reaction can be catalyzed by heme to produce a blue color reaction under acidic conditions

Tetramethylbenzidine (TMB)

A tetramethyl derivative of benzidine. Its oxidation can be catalyzed by heme to produce a green to blue-green color under acidic conditions.

Hemastix® assay kit

TMB-based assay that utilizes a TMB-containing strip device.

chemiluminescence assay

In the ________, light is emitted as a product of a chemical reaction.

Fluorescence Assay

requires the exposure of an oxidized product, such as fluorescin, to a particular wavelength of an excitation light source.

Luminol

It is usually utilized as a chemiluminescent reagent.

Fluorescin

It is used to test for the presence of bloodstains at a crime scene.

Oxidants

Chemicals that are strong oxidants may cause a false-positive reaction.

Plant Peroxidases

It may catalyze oxidation reactions and lead to false-positive results.

Reductants

A false-negative result can occur when a strong reductant is present in a sample.

Microcrystal assays

apply chemicals to treat bloodstains, forming crystals of heme molecules.

Hemochromagens

are heme derivatives in which the ferrous iron of the heme forms two bonds with nitrogenous bases.

Takayama Crystal Assay

A bloodstain is treated with pyridine and glucoseunder alkaline conditions to form crystals of pyridine ferroprotoporphyrin.

Hematin Crystal Assay

Also known as the Teichmann crystal assay.

Hematin

A heme derivative; its iron is in the ferric state.

Chromatographic and Electrophoretic Methods

can identify hemoglobin by its mobility characteristics.

Spectrophotometric methods

_________ for identifying hemoglobin are based on measurements of the characteristic light spectra, with a peak absorbance at 400–425 nm, absorbed by hemoglobin and its derivatives.

Immunological methods

utilize antihuman hemoglobin antibodies. This antibody can be used to detect human hemoglobin and thus indicate the presence of human blood.

RNA-based assays

These assays are based on the fact that certain genes are specifically expressed in certain cell types.