[en] We describe the fairly easy preparation of thiol stabilized water soluble cadmium sulfide quantum dots and the modification of their surface with the human transferrin protein siderophiline. The particles are shown to enable targeted imaging of human breast adenocarcinoma cell (type MCF7). The fluorescence quantum yield of the modified QDs is ∼0.74. The particles have an average diameter of 8.1 ± 0.1 nm as determined in solution by dynamic light scattering. The cancer cells were imaged by fluorescence microscopy of the QDs which display strong green fluorescence under 350 nm excitation. A cytotoxicity assay showed 66 and 78 % cell viabilities, respectively, after 24 h of incubation with the QDs and modified QDs. (author)