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Frontiers of Science: Breaking The Size Barrier of Light


W. Hell, director, Max Planck Institute for Biophysical Chemistry, Gottingen,


Nov. 30, 2010




Wilmot Skaggs Biology Building Auditorium, University of Utah

Stefan W. Hell has developed techniques that allow for light-based microscopes with nanoscale spatial resolution. He will present recent work showing how this optical “nanoscopy” can be used to solve fundamental problems in biology during a free public lecture at the University of Utah on Tuesday, November 30.

Hell will explain how researchers now have a readily accessible tool to explore the relationship between the structure and function of selected cellular organelles, such as the mitochondria.

The Size Barrier of Light

The ability to see the precise spatial and temporal relationships between cellular structures provides biologists and geneticists greater insight in cell development, diseases and mutations.

Lens-based microscopes allow noninvasive three-dimensional imaging of a cell’s interior by taking advantage of the optical transparency of cells. They also enable the detection of specific cellular parts — such as proteins, nucleic acids and lipids–through fluorescence tagging.

Until recently, it was widely accepted that lens-based optical microscopes could not visualize details much finer than about 200 nanometers, which is approximately half the wavelength of light. Yet many cellular processes take place at length scales of tens to hundreds of nanometers.

This so-called “diffraction limit,” or size barrier of light, was the limitation of conventional microscopes for more than a century. To be able to visualize these processes, microscopes with substantially improved resolution were needed.

Two Lasers and a Doughnut Hole

Hell will discuss techniques he uses to circumvent the diffraction limit, including the use of lasers to manipulate the internal states of the molecules making up the sample.

The trick is to use two lasers: one to stimulate molecules in an area, and a second doughnut-shaped laser to deplete the energy of all molecules except those in the center. This method is called Stimulated Emission Depletion (STED) microscopy. The effective size of the doughnut hole, and thus the spatial resolution of the microscope, can be arbitrarily reduced in size by increasing the size of the doughnut ring.

The idea underlying STED microscopy can be expanded by employing a variety of molecules in which the ability to emit light can be switched on or off. This allows for a number of other methods to beat the light barrier in which molecules at unknown positions can be switched on and their positions determined one-by-one to reconstruct a structure at near-molecular dimensions.

About the Frontiers of Science

The Frontiers of Science lecture series is sponsored by the College of Science and the College of Mines and Earth Sciences. Lectures are free and open to the public, but tickets are required to guarantee seating. Visit to reserve tickets.