Greetings Kemin,
Biotinylated antibodies are advantageous because of thier versatility: you
can change the signaling molecules used in your system without aquiring
another set of antibodies, rather a variety of streptavidin conjugated
fluorochromes, colloidal gold spheres, magnetic beads, horseradish
peroxidase etc. may be kept on hand to use with biotinylated antibodies in a
variety of experiments.  If one uses an expensive monoclonal primary
antibody, this can be obtained biotinylated, and so a variety of correlative
studies may be conducted with a minimal investment in antibody reagents.
Kathy makes a good point about endogenous biotin in tissues, however.
Antibody + ProteinA/G conjugated signaling molecules are used for similar
reasons.
    The advantage of fluorochrome conjugated primary or secondary antibodies
is the ease of use.  There is less of an opportunity for something to go
wrong with commercially prepared antibody conjugate reagents.  The
disadvantage is that you need a different fluorochrome conjugated antibody
for each primary antibody used in the system.  This can get expensive and
sometimes wasteful.  In isolated immunolabeling experiments this may not be
a problem, but if your laboratory is involved in a variety of immunolabeling
experiments, it may make more sense to have a large supply of biotinylated
goat anti-rabbit, anti-mouse etc. on hand and a variety of streptavidin
conjugated fluorochromes on hand so investigators can mix and match
according to thier needs.
Regards,
Karl G.
_______________________________________________
Karl Garsha
Light Microscopy Specialist
Imaging Technology Group
Beckman Institute for Advanced Science and Technology
Room B650J
405 North Mathews Avenue
Urbana, IL 61801 USA
Tel: (217) 244-6292
Fax: (217) 244-6219
http://www.itg.uiuc.edu