This paper describes the preparation of bioactive water-soluble fluorescent CdSe/ZnS semi-conductor quantum dots with
a small hydrodynamic diameter of 10 nm. These quantum dots are functionalized with a biotinylated peptide that can be
introduced at different ratios onto the surface of the quantum dots. Their ability to bind to streptavidin in solution is
tested by using gel electrophoresis and fluorescence resonance energy transfer with a fluorescent labeled-streptavidin.
The binding of these quantum dots to Agarose micrometric beads coated with streptavidin is also analyzed by fluorescent
optical microscopy. A synthetic pegylated peptide is successfully used to prevent the non specific adsorption of
streptavidin onto the quantum dots. A specific binding to the streptavidin results in the formation of a very stable
streptavidin-quantum dot complex without any significant aggregation. The average number of streptavidin per quantum
dot is found to be to 4 at the most. Such bioactivate quantum dots can be further conjugated to any biotinylated
biomolecule and used in biological medium.