ATOMIC-FORCE MICROSCOPY IN HISTOLOGY AND CYTOLOGY

This review briefly introduces the principles of the atomic force micr oscope (AFM) and shows our own results of AFM application to biologica l samples. The AFM, invented in 1986, is an instrument that traces the surface topography of the sample with a sharp probe while monitoring the interaction forces working between the probe and sample surface. T hus, the AFM provides three-dimensional surface images of the sample w ith high resolution. The advantage of the AFM for biologists is that A FM can visualize non-conductive materials in a non-vacuous (i.e., air or liquid) environment. AFM images of the plasmid DNA are comparable t o those by transmission electron microscopy using a rotary shadowing t echnique, and have the advantage of examing directly the molecule with out staining nor coating. The surface structure of human metaphase chr omosomes and mouse collagen fibrils demonstrated in air by the non-con tact mode AFM is comparable to that obtained by scanning electron micr oscopy. Quantitative information on the heights of structures is furth er obtainable from the AFM images. Embedment-free thin tissue-sections are useful for observing intracellular structures by AFM. The present review also shows AFM images of living cultured cells which have been collected in a contact mode in liquid. This technique afforded us thr ee-dimensional observation of the cellular movement with high resoluti on. Although there are some innate limitations for AFM imaging, the AF M has great potential for providing valuable new information in histol ogy and cytology.