Atomic force microscope (AFM)



In recent years, tremendous advances have been made in the field of microscopy (the study of microscopes). The electron microscope (which uses a beam of electrons, or negatively charged particles, to form an enlarged image of an object) is found in most hospitals and medical laboratories. The research behind the electron microscope led to Erwin Wilhem Muller's field ion microscope and the powerful scanning tunneling microscope (STM; developed by Heinrich Rohrer and Gerd Binnig), two of the most powerful optical tools in the world. In 1985 a new microscope was added to this list: the atomic force microscope (AFM). The AFM was invented by Binnig, Christoph Gerber of Zurich, Switzerland, and Calvin Quate (1923-) from California.

How AFM Works

The AFM uses a tiny needle made of diamond, tungsten (a hard, heavy metallic element often used in steel production), or silicon (a non-metallic chemical element found in most natural things). The AFM scans its subjects by lightly touching them with the needle. In this respect, it uses the subjects like a phonograph record. The AFM's needle reads the bumps on the subject's surface, rising as it hits the peaks and dipping as it traces the valleys. Of course, the topography (map survey) read by the AFM varies by only a few molecules up or down, so a very sensitive device must be used to detect the needle's rising and falling. In the original model, Binnig and Gerber used a STM to sense these movements. Other AFM's use a fine-tuned laser.

The AFM has already been used to study the supermicroscopic structures of living cells. American physicist Paul Hansma (1946-) and his colleagues at the University of California, Santa Barbara, are quickly becoming experts in AFM research. In 1989, this team succeeded in observing the blood-clotting process within blood cells. Hansma's team presented their findings in a thirty-three-minute movie, assembled from AFM pictures taken every ten seconds.

Other scientists are utilizing the AFM's ability to remove samples of cells without harming the cell structure. By adding a bit more force to the scanning needle, the AFM can scrape cells, making it the world's most delicate dissecting (to take apart) tool. Scientists hope to apply this method to the study of living cells, particularly floppy protein cells. The fragility of these cells makes them nearly impossible to view without distortion.



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