Intro to Serology

Serology

detection of body tissue or fluid at a crime scene

Biological fluids used in serology

blood, semen, vaginal fluid, saliva, urine, feces (sometimes vomit or sweat)

Forensic serologist

links suspect and victim, includes or excludes suspects, establish crime scene, identify weapons, corroborate circumstances

Steps for testing

locate body fluid, presumptive test, confirmatory test

Presumptive test

screening that indicates the possible presence of a fluid of interest, dictates whether further testing is required

Confirmatory test

a test specific to a biological fluid that confirms or denies its presence

Visual examinations

alternate light source and fluorescence

Alternate light source (ALS)

uses specific wavelengths of light to cause an organic stain to fluoresce

Fluorescence

light is absorbed at a specific wavelength moving the molecule to an excited state / molecule moves to ground state emitting a photon at a longer wavelength that can be visually detected

Mark the location of stain

mark stains not visible unless fluorescent light is used (stains that dry clear)

Antigens

foreign substance capable of reacting with an antibody / multivalent antigens have multiple epitopes (binding sites)

Epitopes

portion of the antigen recognized by the antibody (binding sites on antigens)

Antibodies (immunoglobulins)

proteins found in blood and body fluids used by immune system / capable of binding specifically to antigens in order to neutralize them (diversity in amino acid sequences causes binding) / composed of 4 polypeptide chains (2 heavy: fab fragment and fc fragment, 2 light: fab fragment)

FAB

fragment antigen binding

FC

fragment crystallizable

Paratope

site that recognizes the epitope (binding site for antibodies)

Polyclonal antibodies

used for different strains of antigens, makes many types of antibodies

Monoclonal antibodies

makes one antibody, very specific

Steps to make polyclonal antibodies

inject compounds of interest (antigen) into animal, animal signal system reacts to form antibodies from antigens, antibodies are in animal’s blood, scientists collect animal blood

Steps to make monoclonal antibodies

antigen is put in tumor cells, hybridomas form and antigen is now an antibody, tumor cell with antibody divides rapidly and many monoclonal antibodies are made

Antiglobulins

antibodies that specifically react to antibodies/immunoglobulins, it can be nonspecific because it recognizes an epitope that is common to all members of an antibody/immunoglobulin class

Affinity

Strength of interaction of a single epitope of an antigen and single paratope of an antibody (one reactions)

Avidity

overall strength of binding of an antibody and antigen (all reactions)

Primary reactions

initial binding of a single epitope and paratope

Ex of primary reactions

immunoassays and immunochromatographic assays

Secondary reactions

reactions that follow primary reaction

Ex of secondary reactions

precipitation and agglutination

Immunoassays (primary)

antibody sandwich enzyme linked immunoabsorbant assay (ELISA) is most common

Immunochromatographic assays (primary)

uses an immunochromatographic membrane device / rapid and simple test / false negative if there is too high of a concentration of antigen (high dose hook effect)

Precipitation reactions (secondary)

occurs when a soluble antigen binds to an antibody / forms an insoluble complex which precipitates out of solution / precipitin curve forms 3 zones: prozone, zome of equivalence, post zone

2 types of precipitation reactions

radial and double

Prozone

too much antibody, no result

Zone of equivalence

enough antigens and antibodies, positive result

Post / excess zone

too many antigens, no result

Agglutination reactions (secondary)

when an antigen is located on a cell’s surface and binds to an antibody, it causes the cells to clump together / used for ABO blood typing

Handling of biological evidence

collect after documenting or photographing scene and maintain chain of custody for each piece of evidence

Collection guidelines for visible stains

moisten sterile cotton swab and rub stain of interest

Collection guidelines for non-visible stains

swab first with moistened swab, followed by dry swab (wet/dry technique)

Collection guidelines for wet/liquid stains

use dry swab to collect

Special handling

preserve bloodstain patterns or possible trace evidence / do nondestructive analyses first when multiple analysis of evidence is needed / use universal precautions when handling all biological evidence

Substrate control

collect samples from a control area (unstained area near a collected stain)

Chain of custody

form of documenting evidence authenticity / who is handling evidence, where is evidence located, what is done to evidence, how much evidence is used

Packaging and transport

designed to protect and preserve evidence / avoid exposure to heat or humidity / allow all wet stains or swabs to air dry before packaging / multiple swabs of same stain or area may be packaged together

Packaging and transport for evidence from different sources

do not group evidence in a single package (contamination)

Packaging and transport for folding of evidence

folding of clothing (especially wet clothing) can transfer evidence / place clean sheets of paper between layers of dry garmets

Packaging and transport for packaging materials

paper items (envelopes, bags, boxes) should be used, do not seal in plastic

Packaging and transport for liquid evidence

tubes should not be frozen, place tube in plastic bag to prevent leaks

Packaging and transport for trace evidence

wrap in paper secured with a druggist’s fold, packed in paper envelope or bag

Label packaged evidence with

case number, item number, date, item description, source, location

Label evidence tape with

initial and date