CFTR (cystic fibrosis transmembrane conductance regulator) exists in macromolecular complexes in the plasma membrane. However, it is yet unclear whether clustering is a result of cAMP stimulation. Therefore we investigated the rearrangement of CFTR molecules in 16HBE14o- cells upon stimulation using immunostaining with quantum dots (QDot) labelled antibodies. These nanocrystalline fluorophores resist bleaching and blink. Fluorescence and atomic force microscopy were used to identify and to quantify CFTR in the plasma membrane. Blinking analysis allows distinguishing between QDots located in close vincinity, far beyond the optical resolution of fluorescence microscopy. Experiments reveal that CFTR molecules exist unclustered in unstimulated cells whereas CFTR clusters are detected in plasma membrane after stimulation. The results were confirmed with atomic force microscopy. Phase imaging, an extension of the tapping mode, detects material properties in parallel to topography. Since QDots are nanocrystals and much harder than the cell membrane. Phase imaging allows the identification and quantification of QDots within the wrinkled cell membrane. Taken together we conclude that stimulation of 16HBE14o- cells induces clustering of CFTR in the cell membrane.