Serial Block-Face Scanning Electron Microscope (SBEM)

 

With the serial block-face scanning electron microscope, details of a tissue sample can be automatically captured and displayed in high-resolution, three-dimensional form.

The serial block-face scanning electron microscope consists of a scanning electron microscope, an ultra-microtome located inside of its vacuum chamber, and a moving sample stage.

In preparation for an image, a tissue sample is first prepared using a special procedure and then embedded in epoxy resin. In the vacuum chamber of the scanning electron microscope, the surface of the sample is then scanned by an electron beam. The resulting image is saved. The ultra-microtome then cuts off a layer only a few millionths of a millimeter (nanometer) thick from the surface of the sample. The sample is then moved back to the same position into the focal plane of the electron beam and scanned for the next image.

The automated process of scanning and cutting produces a three-dimensional image of the tissue sample. This can be analyzed by computer with the help of artificial neural networks.

In contrast to light microscopes, a scanning electron microscope can make significantly smaller details visible – up to a resolution of a few nanometers. In the serial block-face scanning electron microscope, even synaptic vesicles become visible. The finest nerve cell extensions with all their branching can be displayed three-dimensionally. The automated process replaced the time-consuming and error-prone production of serial cuts.

The method was published in PLOS Biology in October 2004:
Winfried Denk & Heinz Horstmann
Serial Block-Face Scanning Electron Microscopy to Reconstruct Three-Dimensional Tissue Nanostructure