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ANALYTICAL CURRENTS
Mice glow with quantum dots The use of quantum dots as labels in biological studies has recently caught on. Alan Waggoner and colleagues at Carnegie Mellon University and Quantum Dot Corp. have now fueled some more excitement by imaging the entire bodies of live mice injected with quantum dots. Quantum dots are nanocrystals of semiconducting material that emit electrons of precisely defined wavelengths upon excitation. A primary obstacle to using quantum dots in biomedical applications has been the inability to stably maintain them in solution and chem-
A live mouse injected with PEG-modified quantum dots glows under a fluorescent microscope.
ically modify them. To overcome this limitation, Waggoner and colleagues designed quantum dots with four different surface coatings. The group found that a coating of an amphiphilic poly(acrylic acid) stabilized the quantum dots in solution. They could then create three more types of quantum dots modified with different lengths of polyethylene glycol (PEG). The four types of quantum dots were injected into live mice, and localization of the quantum dots was tracked by fluorescence microscopy. The quantum dots modified with the longest chain of PEG were most stable in vivo, circulating in the mouse bloodstream for >3 h, while the shorter PEG-modified and poly(acrylic acid) quantum dots were cleared from circulation in
