A) Scheme of the derivatization of the QDs by double ligand exchange. Surface TOPO is replaced with MPA followed by the partial replacement of the MPA with thionylated oligonucleotides. B) Luminescence spectra of TOPO-QDs (solid line) and their corresponding oligonucleotide derivatives respectively (dashed line). Original emission-wavelength is slightly shifted to the red by TOPO replacement. C) TEM-picture of QD-oligonucleotide derivatives. There are no agglomerates observed after surface modification.