A newly developed coating allows quantum dots — considered toxic and unsuitable for use in living organisms — to be used inside the human body, even inside living cells. Scientists studying biological processes often use fluorescent tags that bind to biomolecules. This makes it relatively easy to track such molecules, even inside living cells. Quantum dots, however, are a better option — they emit long-lasting, bright light, the color of which depends on the size of the quantum dots used. But the problem with quantum dots is that they do not dissolve in water. Quantum dot with an amphiphilic coating, at which other polymer chains can be ‘clicked’ to form new combinations with other quantum dots. (Image: University of Twente) The new coating, developed by researchers at the University of Twente’s MESA+ Institute for Nanotechnology and at the A*STAR agency in Singapore, not only improves solubility in water, but also enables other molecules to lock onto its surface. This 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; i.e., one with both hydrophobic and hydrophilic properties. The “water hating” side of the polymer material attaches to the surface of the quantum dot. Its exposed hydrophilic side 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. Besides the added benefit that other molecules can be bound to it, the coating polymer does not adversely affect the quantum dot’s light-emitting properties. The research was published in Nature Protocols. For more information, visit: www.utwente.nl/en