Atomic force microscopy of embedment-free sections of cells and tissues

The atomic force microscope (AFM) was applied for the first time to embedment-free biological sections. Aldehyde-fixed tissues (kidney, liver etc.) of mice were postfixed with osmium tetroxide and cut into 500-700 nm thick sections after embedding of the tissue block in polyethylene glycol (PEG); the sections mounted on glass slides were deembedded and critical point-dried. The AFM images were collected in air from those tissue sections in a dynamic force mode. Solid-height-mode images, which were comparable to transmission electron microscope (TEM) images, seemed to provide us more useful information than the solid-mode images which resembled scanning electron microscope (SEM) images. Internal structures including chromatin fibers in the nuclei and cytoplasmic organelles were clearly recognizable by AFM. Minute surface structures including the end-feet of renal podocytes were demonstrated. We confirm that a vertical resolution of 0.1 nm and a lateral resolution of 5-10 nm are attainable with the dynamic force mode of AFM using thin sections of tissues. The present paper proposes the usefulness of AFM for observation of biological materials without metal coating in a non-vacuous environment.