Carmichael, Stephen W.

Abstract In high resolution imaging of biologic structure, atomic lorce microscopy (AFM) has been prevailing over scanning tunneling microscopy (STM). This is primarily because biologic materials do not conduct electricity, and STM requires that electrons flow to or from the surface of the specimen, whereas electron flow is not required for AFM. Microscopists intent on using STM have compensated by coating specimens with a thin coat of metal. However, the presence of metal atoms on the surface degrades the resolution. A new development may make STM more useful to biologists than ever before.

Abstract It must have seemed rather fantastic back in the fifties, when Russell Steere froze chunks of plant viruses (tobacco mosaic virus, tobacco nngspot virus, and squash mosaic virus) in drops of water, planed them freehand with a scalpel blade, made a replica of the surface, and examined the replica in a transmission electron microscope. But that was the birth of freeze-fracture and freeze-etch methodology that yielded enormous amounts of information about the morphology of membranes.

Abstract It is impressive enough that individual atoms can be resolved with the atomic force microscope (AFM), but who would have thought that atomic motion would be detected so soon? Atomic resolution with the AFM was only recently achieved. As reported in this column, Franz Giessibl was able to demonstrate local resolution of adatoms of the Si(111) 7×7 reconstructed surface. Now, Yasuhiro Sugawara. Masahiro Ohta, Hitoshi Ueyama, and Seizo Morita of Hiroshima University have demonstrated atomic resolution of the surface of InP(110). Not only that, but images taken about one minute apart show that some of the atoms had moved! Sugawara et al, used a very compact AFM under ultrahigh vacuum (4 X 10-8 Pa) to accomplish this impressive feat. A stiff (spring constant of 34 N/m) silicon cantilever was used. This stiffness, along with a mechanical resonant frequency of 151 kHz, was used to keep the cantilever from jumping onto the sample and crushing the initially sharp tip.

Abstract When most of us use a microscope, we are looking through a specimen, or more and more frequently, at the “top” surface. It usually doesn't occur to us to look sideways. But that is what was done recently in the laboratory of Charles Lieber at Harvard University. As reported by Daniel Frisbie, Lawrence Rozsnyai, Aleksandr Nay, Mark Wrighton, and Prof, Lieber, an atomic force microscope (AFM) was modified to perform as a “chemical force microscope” (CFM). With the CFM they were able to precisely measure adhesive and frictional forces. These forces can be thought of as acting parallel to the surface of the specimen, whereas most observations are made perpendicular to the surface.

Abstract The process of ultra-miniaturization has been termed nanofabrication. It looks like the scanning tunneling microscope (STU) and related microscopes will be players in this technology of the future. One of the most recent contributions has been the demonstration that single molecules can be “pushed” across a surface with the STM. This remarkable achievement was demonstrated by Thomas Jung, Reto Schlittler, and James Gimzewski of the IBM Zurich Research Laboratory and Hao Tang and Christian Joachim of the National Center for Scientific Research in Toulouse, They were able to position intact individual molecules on a two-dimensional surface at room temperature by a controlled “pushing” action of the tip of a STM. Similar positioning feats have been done at low temperatures while thermal motion is limited.

Abstract We think that adhesion molecules hold cells together. This is the "glue" that holds us, and every other multicellular life form on this planet, together. Intriguingly, the atomic force microscope has recently been used to directly measure the binding force of one of these adhesion molecules. We now have direct evidence that adhesion molecules have the physical properties required to hold cells together. This essential new information shows that these molecules can perform the function that have been assigned to them. You'll be delighted to know that this molecule is more than strong enough to do its job!

Abstract If you have been hibernating for several weeks you may have missed the headlines and magazine covers exclaiming about “Life on Mars!” The basis for all of this excitement is an article in Science by Dr. David S. McKay of the Lyndon B. Johnson Space Center in Houston and eight of his colleagues from several academic institutions. The reader of this column will not be surprised by the fact that microscopes were used to detect evidence of life on a meteorite from Mars. The first consideration was whether or not the meteorite was in fact a fragment of the martian surface. The specimen, known as ALH84001, is from a class of meteorites that appear to have resulted from impacts on Mars, some of the specimens landing in Antarctica where this one was recovered. Trapped gases (in glass droplets and stringers) in several of the family of meteorites closely match the martian atmosphere for several gases over 8 orders of magnitude range in abundance. Whereas ALHB4001 did not contain such trapped atmospheric gases, its elemental and isotopic composition closely resemble the meteorites that do.

Abstract Historically, microscopes have been used to gather morphologic data. We have called people who use these instruments microscopists, and it is implied that microscopists are morphologists. As was pointed out in the April/May issue of this newsletter, useful information about a specimen is also gained from temporal analysis. Further, it has been appreciated that the new family of scanning probe microscopes can be used to gather additional types of information so that these instruments have the potential to be useful beyond the dreams of a conventional microscopist. As we will discuss in this article, the future is here for one such application. The atomic force microscope (AFM) takes advantage of the leverage afforded by the deflection of a laser beam bounced off a cantilevered stylus that is scanned over the surface of a specimen.

Abstract Microscopes are known for demonstrating structure, but there have been many examples of how this is changing. A novel use of the atomic force microscope (AFM) by Manfred Radmacher, Monika Fritz, Helen Hansma, and Paul Hansma at the University of California, Santa Barbara, has extended the versatility of this instrument even further. They demonstrated a conformational change in a molecule that happened in a fraction of a second. Radmacher et al. pointed out that enzymes perform their biologic function by undergoing a conformational change and that this change is within the spatial and temporal resolving capabilities of the AFM. They set out to prove this by lowering the tip of the AFM onto lysozyme, a molecule that is roughly egg-shaped, measuring about 4.5 nm by 3 nm by 3 nm. Using the tapping mode in liquid, they found that single molecules exhibited a spike-like height fluctation when in the presence of a suitable substrate.