Thick-Shelled Quantum Dots Blink Less

Fluctuations in the emission intensity of individual fluorophores, a phenomenon known as blinking, can be a problem when those fluorophores are used as labels in single-molecule experiments. In a study led by Jean-Pierre Hermier and Benoit Dubertret, both with France's National Center for Scientific Research, researchers have found that semiconducting nanocrystals—known as quantum dots (QDs)—that have thick shells blink less than thinner shelled ones (Nat. Mater., DOI: 10.1038/nmat2222). Separately, a team led by Jennifer A. Hollingsworth of Los Alamos National Laboratory has also reported reduced blinking with thick-shelled QDs (J. Am. Chem. Soc. 2008, 130, 5026). The French team synthesized 13-nm-diameter QDs with a 2.5-nm CdSe core and a layered CdS shell and detected the fluorescence of individual QDs using a charge-coupled device camera. At 30-millisecond exposure times per frame, two-thirds of the QDs emit continuously for five minutes without blinking. At longer exposure times even more of the QDs don't blink. The nonblinking behavior depends on the thickness of the CdS shell. "Well-designed shells are the key parameter for obtaining nonblinking QDs," the French researchers write.