Application Introduction

Chicken avidin is a tetrameric protein containing four identical subunits, binding biotin with a high degree of affinity and specificity. These properties have led to the use of the avidin-biotin system (ABS) in a wide variety of applications of life sciences, including purification, diagnostic and modern in vivo medical applications where it is used for localization, imaging and targeting of cancer cells and tumors.

Applications of the Avidin-Biotin System (ABS)

Affinity Targetting/Diagnostics
  Crosslinking Agents   Isolation Studies  
Affinity Targeting Affinity Perturbation Avidin Conjugate Selective Elimination Immobilising Agents
Fusogenic Agents Drug Delivery    
Affinity Therapy Pathological Probes Affinity Cytochemistry Flow Cytometry
Cytological Probes Blotting Technology Biotinylated Binder Light Microscopy Localisation Studies
Epitope Mapping Bioaffinity Sensors Electron Microscopy Fluorescent Microscopy
Gene Probes  

Target Molecule

Binding/Signal

Signal Amplification Histo Chemistry
      Immuno Assay


What is an ELISA test?

ELISA is an acronym for "enzyme-linked immunosorbent assay" test. It uses components (antigens & antibodies) of the immune system in conjunction with chemical reactants (ie ABS) to detect immune responses in the body. Such tests traditionally involve an antibody or antigen (immunologic molecules) and an enzyme conjugate (ie peroxidase-avidin) that catalyzes a detectable biochemical reaction in vitro. They are widely used in the detection of substances that have antigenic properties, ie proteins, hormones, and the like. Their sensitivity and specificity are very high in comparison to other methods. ELISA tests are also one of the cheapest diagnostic methods, when applicable.

 

Examples

In vitro application: Pregnancy tests rely on the presence of a hormone, ie human chorionic gonadotropin (hCG), a glycoprotein secreted by the placenta shortly after fertilization. These tests target the hCG hormone, from either blood or urine, with a specific antibody and use the ABS (a conjugated avidin) as an indicator. The antibody binds selectively to hCG, leaving all other hormones blind. The ABS indicator reveals the eventual presence of the hormone by developing a specifically-colored chemical that appears in the pregnancy test. Highly sensitive tests conducted in specialized laboratories can use a fluorescent or radioactive molecule attached to the antibody. The avidin is used to bind the fluorescent molecule and the antibody.

 

In vivo application: The innocuous affinity of avidin for specific tumor receptors is used for its targeting of tumor cells in vivo and for targeting radionuclide-derived radioactive biotin:

  • A fusion protein named Scavidin, consisting of the macrophage scavenger receptor class A and avidin, has been shown to be binding and internalizing by tumor cells.