Quantum dots, discovered in the 1990s, have a wide range of applications and are perhaps best known for producing vivid colors in some high-end televisions. But for some potential uses, such as tracking biochemical pathways of a drug as it interacts with living cells, progress has been hampered by one seemingly uncontrollable characteristic: a tendency to blink off at random intervals. That doesn't matter when the dots are used in the aggregate, as in TV screens, but for precision applications it can be a significant drawback.