Brighter bulbs light up cell innards.

Biologists spying on the inner workings of cells often attach tiny fluorescent beacons to molecules to track their movements under laser light. The organic dyes used for that purpose, however, typically dim in minutes. Their quick demise frustrates attempts to follow longer-lasting phenomena.

Now, two research groups report fabricating an improved type of cellular lightbulb from clusters of semiconductor atoms known as quantum dots. Quantum dots are remarkable because they confine electrons to an unusually small volume, giving them special light-emitting properties (SN: 11/23/96, p. 327). Researchers at Indiana University in Bloomington say their dots glow 20 times brighter and 100 times longer than dye molecules.

"This is a new class of labels that could replace the organic dyes," says Indiana's Shuming Nie.

The Indiana group and, independently, a team at Lawrence Berkeley (Calif.) National Laboratory report in the Sept. 25 Science using quantum dots to illuminate molecules in cells.

Electrons in fluorescent materials absorb energy from light and rerelease it as photons of a particular colon Nie explains that quantum dots blaze brighter because, though small, they are much bigger than dye molecules.

At up to 6 nanometers across, the dots can have 200 times the volume of the dye molecules, which are typically less than a nanometer across. Consequently, the dots can absorb more light and, in turn, emit a stronger glow when excited. A protective coating extends their brilliant careers.

Because varying the size of dots forces the electrons in them to absorb and reemit light of different wavelengths, researchers have found they can choose a dot's color by controlling its size. Crystal bends light hard, saves space