Herein we report a new and simple method of in situ functionalization of CdSe QDs and surface passivation by a thin ZnS shell at the same time. This method avoids a second-step ligand exchange after the core-shell formation and preserved high quantum yield of the QDs. We demonstrated that such prepared QDs can serve as excellent nanomaterial for bioconjugation. Different antibodies were conjugated to the MPA-functionalized QDs and resulted in highly stable and highly photoluminescent nanoparticles for cell labeling purposes.