Labeled Avidin Binding (LAB) Method*

The labeled avidin binding (LAB) method is the latest method to use the avidin-biotin technology. It provides even more sensitivity than either the standard peroxidase-antiperoxidase (PAP) or avidin-biotin complex (ABC) methods see Chapter 20 and Chapter 21 ) (1 ). The technological difference from these methods is that the enzyme peroxidase is covalently linked directly to the avidin molecule. This enhances sensitivity, since the avidin molecule can be labeled extensively with enzyme and the complex remains relatively small. The small size enables many avidin molecules to bind to the biotinylated secondary antibody (2 ). In addition, the biotin is more accessible since it is positioned on a long carbon arm extension from the secondary antibody, reducing steric hindrance (see Fig. 1 ). With the numerous enzyme-labeled avidin molecules able to attach to any biotin on the secondary antibodies, the sensitivity and the resolution of this technique are superior (3 ). The avidin molecule in use in this system is generally obtained from Streptomyces avidinii bacteria and is called streptavidin, a molecule with a more neutral pH and a reduced tendency toward inappropriate binding (4 ). This method also lends itself to further amplification through the use of antibodies to biotin, avidin, or both.