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Modifying Nanocrystal Surfaces for Molecular Imaging and Electrical Devices



  • Fluorescent labeling
  • Biological sensing - Forster Resonance Energy Transfer (FRET)
  • Electrical devices (sensors, LEDs, photovoltaics)
  • Catalysis
  • Fillers in composite materials


  • Smaller probe enables improved mobility within the cell
  • Can be used to enhance insulation or conduction in electronic devices
  • Any suitable material having a silicon bond can be used as reactant
  • Produces more precise NMR readings


Berkeley Lab's Paul Alivisatos and Jonathan Owen have discovered fundamental principles that enable them to control the surface chemistry of semiconductor nanocrystals, or quantum dots. The new nanocrystals are made by chemically cleaving surfactant-nanocrystal bonds and attaching a desired ligand at the site.  

Current quantum dot technologies are physiologically too large to disperse effectively to all desired areas in the cell because water-soluble, globular polymers have to be attached to the dots to allow movement at the cellular level. These complexes can range from 20-30 nm. The Berkeley Lab probes are water soluble and mobile and range in size from 4-8 nm, consisting of just the nanocrystal and the desired ligand.   Because the Berkeley Lab probes are so small, their improved mobility within the cell allows imaging of smaller features such as neuronal synapses and perhaps even the contents of a cell nucleus.

The Berkeley Lab-processed nanocrystals have applications beyond imaging. They can   also be used as functional elements in optical, photovoltaic, and electrical devices, as fillers in composite materials, or as catalysts. Replacing the native surfactant ligands with chloride or other halides will have a significant impact on the electrical properties of these nanocrystals.   If halides are used as surface atoms, the processed nanoparticles could be valuable in electronics applications by providing better electrical conduction or insulation.  

The Berkeley Lab technique enables the removal of surfactant ligands containing acidic binding groups from the surfaces of nanocrystals via a chemical reaction with a silicon-containing compound. The procedure results in a quantum dot with a new ligand attached to the base material. The reaction also can be manipulated such that the processed nanoparticle would contain a mixture of the first and second ligands on its surface.

In addition to the applications described above, the Berkeley Lab synthetic methods also makes it possible to accurately characterize surface ligands more rigorously than has been possible before.


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