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Getting Microscopic: Investigating molecular issues at the source

BY A. J. HOGG

Published April 10, 2006

"Then you learn something about the forces these enzymes can exert on their substrates," Walter said.

Atomic force microscopy

A third way of looking at single molecules is a technique called atomic force microscopy. Using this method, researchers set a cantilever with a very fine point (similar to a very small version of the needle on a record turntable) to measure the surface of a cluster of molecules. The top of the cantilever is reflective. When a laser reflects off the cantilever, a photodiode measures how much and in which direction the cantilever moves. The measurement is accurate to one nanometer.

The cantilever moves over the surface in meanders, scanning it to give an image of the surface topography.

Individual molecules can also be pulled from the surface with the tip. Sometimes a molecule sticks to the cantilever and gets pulled out of the surface. By measuring the force it takes to pull the molecule off, researchers can learn about how the molecule is folded or threaded in the surface.