By Peter Weiss
The delicate touch of visible light allows scientists to peer into living cells without disrupting them. However, to discern the subtlest details, optical microscopes have long been considered too crude a tool. Instead, researchers have developed techniques such as electron microscopy to make out the finest features, but only in dead specimens.
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Enter the stimulated emission depletion microscope. This novel optical device harmlessly resolves fluorescently labeled bits of living cells that are smaller than the so-called diffraction limit, say its developers at the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany. Because light bends, or diffracts, around the edges of objects, ordinary optical microscopes can discern features no closer than a half-wavelength apart, a distance of 200 nanometers (nm) or so.