Development of an Atomic Force Microscope Suitable for Observation of Biological Samples.

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Atomic force microscopy(AFM)holds great promise for biological science, since it allows us to observe with nanometer resolution the native surface structure of protein in an aqueous environment, and further it can quantify force exerted between the surfaces of protein and the tip of an AFM probe(or a second protein attached to the probe tip). Commercially manufactured atomic force microscopes are, however, inadequate for the biological application, since blind scanning has to be made to locate objects of interest randomly distributed on the sample substratum. To overcome this problem, we have developed an atomic force microscope integrated with an inverted fluorescence microscope. The Z-actuator is a short hollow piezo tube, on the top of which a sample is placed. The objective lens is inserted from the bottom into the hollow space. Since this piezo tube is wide (inner diameter 3.5cm), its top cannot deflect much in the XY directions. As XY actuator two piezo plates pointing at right angles to each other are placed horizontally with their tips touching a hollow plate(glued to the bottom of the Z-piezo tube)on the sides. The location of the probe tip as well as individual protein molecules that are stained with fluorescent dye can be visualized under the fluorescence microscope. By the use of an XY-stage to move a sample and another XY-stage to move the AFM head(including the probe tip), the probe tip can pinpoint a specific object of interest. This ensures an obtained AFM image to be of the object, neither of contaminants nor of an undulation of the substratum. Further, it facilitates the capture of single protein molecule at the tip of the probe. Using the developed AFM,we obtained clear images of a single actin filament and two-headed structure of myosin. We succeeded in capturing a single myosin molecule at the tip of the probe, utilizing the strong affinity between avidin and biotin.