In July 1985, three physicists—Gerd Binnig of the IBM Zurich Research Laboratory, Christoph Gerber of the University of Basel, and Calvin Quate of Stanford University—puzzled over a problem while schmoozing at a microscopy workshop in the Austrian alps: How could they accurately visualize biological material without destroying it?
The scanning tunneling microscope, which Binnig had co-invented 4 years earlier, provided atomic resolution without the need for ultra-low temperatures. But it relied on an electric current flowing through conductive materials. Thus, viewing biological samples—especially living cells—was out of the question.
At the workshop, the trio fleshed out a new idea: Instead of measuring voltage fluctuations, they could simply look for fine-scale changes in miniscule van der Waals or electrostatic forces. Without the need for a current, such an "atomic force microscope" (AFM) could reveal the structure of nonconductive materials such as proteins, organelles, and...
Immediately thereafter, the three physicists began working "day and night" to build a prototype, says Gerber. The hard work quickly paid off. A mere 6 months later, the researchers achieved their first atomic-scale resolution image of a single graphite crystal. "We were so satisfied that at six o'clock in the morning we just stepped out of the lab and played a round of golf," Gerber says.
The first prototype AFM (shown here) was rigged to cords and fitted with metal plates to prevent vibration. On top, a tiny cantilever tip similar to a needle in a record player grazed across the surface of a material and bent ever-so-slightly in response to slight atomic force variations. The tip's deflection was then translated into a three-dimensional image of the sample.
Since then, the simplicity of the AFM concept has spawned dozens of variations and has been used to explore the terrain of biofilms, measure forces in motor proteins, and track nanoparticles coursing through a living cell. In the past 25 years, "people have developed it into the most powerful and most sensitive surface characterization tool that we have," Gerber says.
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