Katsuhide Mabuchi, Ph.D., Senior Research Associate
An electron microscope (EM) enables us to magnify objects much more than the light microscope (LM) can. A bacterium looks like a grain of rice with LM, while you can see its detailed inside features with EM. How does EM provide so much higher magnification? Light travels like a wave; different colors of light have different wavelengths. For example, blue light has a shorter wavelength than red light. The wavelength of light sets the limit on the size of the object you can see. EM uses electron beams, which can also be viewed as waves but with much shorter wavelengths than light, hence allowing us to see smaller objects.
But unlike LM, you can’t just put the specimen on a microslide and observe by EM because of two major problems. First, while light can penetrate thick glass, even air blocks electron beams. Therefore, the electron beams must be confined in a vacuum tube and specimens must not contain any liquid that may vaporize in the vacuum. This means it is impossible to observe a biological specimen as is. Secondly, biological specimens are almost transparent to electron beams, just like glass to light, and internal structures are not revealed unless they are “stained.” Among the many ways to visualize samples is a technique called “rotary shadowing,” in which protein molecules are coated with a thin layer of a heavy metal (e.g. platinum). Because heavy metals block electron beams, they can reveal the shape of transparent objects.
EM helps scientists to visualize the surface of cells, the structure of membranes and particles inside the cell, and the shape of individual protein molecules. From the images of these biological elements it is often possible to deduce their functions. For example, the current theory about how muscles contract was proposed based on the shapes and movement of myosin and actin filaments observed with EM.
Electron microscopy uses electron beams, which can also be viewed as waves but with much shorter wavelengths than light, hence allowing us to see smaller objects.