Ludwig-Maximilians-University, Center of NanoScience, Amalienstr. 54, D-80799 Munich, Germany
Colloidal nanocrystals are building blocks of the "nanoworld" with a variety of interesting features. Their electronic properties enable the building of single-electron transistors, and their optical properties can be used to generate fluorescence labels with many different colors. However, in order to fully exploit these properties, besides the creation of the individual building blocks also the ability to arrange these building blocks to desired patterns or positions is of great importance. Based on the principles of molecular recognition and self assembly biological molecules can be used to arrange nanoscale building blocks. If certain receptor-molecules are attached to a nanoscale building block, the receptor-conjugated building block will bind with high selectivity to all areas, where ligand-molecules are present. Based on the key-lock binding mechanism of receptor-ligand systems, nanoscale building blocks can be directed in this way to desired positions. Two applications will be discussed. Colloidal gold nanocrystals were conjugated with a controlled number of DNA molecules per nanocrystal. By using complementary sequences of DNA molecules that were attached to different nanocrystals, small groupings of gold nanocrystals as dimers and trimers could be formed. The structure of these groupings, the limits of this technique and the structure of the indiviual DNA nanocrystal conjugates will be discussed. Biomolecule conjugated colloidal semiconductor nanocrystals can be used to fluorescence label structural compartments of cells. These nanocrystals were also found to be actively incorporated by living cells. It will be described how cells "eat" nanocrystals and an assay for cell mobility based on this fact will be introduced.
This work was done during a post doctoral visit in the group of Prof. Paul Alivisatos, University of Berkeley, California, U.S.A.