1. Different lighting sources
The illumination source used in the microscope is the electron flow emitted by the electron gun, and the illumination source of the optical microscope is visible light (sunlight or light). Since the wavelength of the sub-flow is much shorter than the wavelength of the light wave, the magnification and resolution of the electron microscope are significantly higher than that of the light mirror. .
2. Different lenses
The objective lens that magnifies in the electron microscope is an electromagnetic lens (a ring-shaped electromagnetic coil that can generate a magnetic field in the center), and the objective lens of an optical microscope is an optical lens made of glass. There are three groups of electromagnetic lenses in electron microscopes, which are equivalent to the functions of condenser objective and eyepiece in optical microscopes.
3. Different imaging principles
In the electron microscope, the electron beam acting on the sample to be inspected is magnified by an electromagnetic lens and then hits a fluorescent screen for imaging or acts on a photosensitive film for imaging. The mechanism of the difference in electron density is that when the electron beam acts on the sample to be tested, the incident electrons collide with the atoms of the substance to generate scattering, and different parts of the sample have different scattering degrees for the electrons, so the electron image of the sample is presented in shades. The object image of the sample in the optical microscope is presented with a difference in brightness, which is caused by the difference in the amount of light absorbed by the different structures of the sample.
4. Resolution
Because of the interference and diffraction of light, the resolution of optical microscopes can only be limited to 02-05um. Because electron microscopes use electron beams as light sources, the rate of failure can reach between 1 and 3 nm. Therefore, the tissue observation of optical microscopes belongs to micron-level analysis, and the tissue observation of electron microscopes belongs to nano-level analysis.
5. Depth of Field
Generally, the depth of field of an optical microscope is between 2-3um, so the surface smoothness of the sample is extremely demanding, so the sample preparation process is relatively complicated. The spirit of SEM can be as high as several meters, so there is no requirement for the smoothness of the sample surface geometry, the sample preparation is relatively simple, and some sample geometries do not require sample preparation. Stereo microscopes have a relatively large depth of field, but their resolution is very low.
6. Different specimen preparation methods are used
The preparation procedure of tissue and cell specimens used for submicroscopic observation is complex, with high technical difficulty and cost. Special reagents and operations are required in the steps of sampling, fixation, dehydration and embedding. Finally, the embedded tissue blocks need to be Put it in an ultramicrotome to cut into ultrathin specimens with a thickness of 50 ~ 100nm. Specimens observed by light microscopy are generally placed on glass slides, such as ordinary tissue slice specimens, cell smear specimens, tissue pressed specimens and cell drop specimens.
7. Magnification
The effective magnification of the optical microscope is 1000X. The effective magnification of a good electric microscope can reach 1000,000X.
