A super-high-resolution 3-D light microscope developed at the Max Planck Institute for Biophysical Chemistry will allow biologists to watch the workings of the tiniest organelles and even individual clusters of proteins in living cells. The new technology, which has a resolution of 40 nanometers, overcomes some major limitations in existing microscopy techniques and could have important applications in dissecting exactly how drugs impact cells.

"[It's] a tour de force--a major accomplishment," says John Sedat, a professor of biochemistry and biophysics at the University of California, San Francisco. Using the Max Planck microscope and others that are pushing nanoscale resolution, biologists will be able to watch how live cells work at an unprecedented level of detail. "It's going to be a revolution for biology," says Sedat, who was not involved in the research.

In recent decades, biologists have made great strides in understanding the molecular makeup of cells, but how these parts add up to functioning cells and tissues is still something of a mystery. Using light microscopes, biologists can watch living cells at relatively low resolution; using electron microscopy, they can carefully dissect dead cells.

The new microscope "allows you to optically dissect living cells," says Stefan Hell, head of the department of nanobiophotonics at the Planck Institute, in Göttingen, Germany, who led the instrument's development.

Researchers used the new microscope to make the first super-high-resolution light images of tiny cell organelles called mitochondria, which are crucial for cell metabolism and play a role in the aging process. One potential application is to visualize how certain cancer drugs affect the mitochondria, whose inner workings have been invisible to 3-D light microscopy. "It's been difficult because you couldn't see molecules binding to each other," making it impossible to definitively name the cause of these drugs' effects, says Maryann Fitzmaurice, a pathologist at Case Western Reserve University, in Cleveland.

Three-dimensional light microscopes work by scanning a focused spot of light through cells in three planes. The size of this spot limits the resolution of the microscope--nothing smaller than the size of the spot can be seen. Due to a fundamental property of light called the diffraction limit, focusing light down to a size smaller than half its wavelength is impossible using conventional lenses. Many parts of the cell are smaller than half the wavelength of the light used for these techniques. Other researchers have gotten around the diffraction limit in two dimensions, or with techniques that only work with a particular wavelength of light.