Polymer-coated quantum dots 'shine' inside living cells

Quantum dots emit more intense and longer-lasting light than that produced by fluorescent markers, but they do not dissolve in water and pose toxicity risks for use in living organisms. Recognizing this setback, researchers at the University of Twente's MESA+ Institute for Nanotechnology (Enschede, The Netherlands) and at the A*STAR Institute of Materials Research and Engineering in Singapore have developed a coating that allows quantum dots to be used inside the human body—even inside living cells.

The new coating enables quantum dots, which are semiconductor nanocrystals, to cast light on biomedical processes. These dots consist of several hundred to several thousand atoms that emit visible light when they are exposed to invisible UV radiation, for example, and range from a few to several tens of nanometers in size. The coating's benefits are not limited to improved solubility in water alone. Other molecules can "lock on" to its surface, which could make coated quantum dots sensitive to certain substances, for example, or allow them to bind to specific types of cells, such as tumor cells.

The researchers developed an amphiphilic coating, which pairs hydrophobic and hydrophilic properties. The "water hating" side of the polymer material attaches to the surface of the quantum dot. Its exposed hydrophilic side then makes the quantum dot/coating combination soluble in water. The coating builds up on the surface of the quantum dot through a process of self-assembly. The coating polymer has the added benefit that other molecules can be bound to it. Another important plus is that it does not adversely affect the quantum dot's light-emitting properties.

The researchers published their work in the October issue of Nature Protocols. For more information, please visit http://www.nature.com/nprot/journal/v6/n10/abs/nprot.2011.381.html.