An Article to Understand the Differences Between Electron Microscopes and Optical Microscopes
An electron microscope is a large instrument that uses an electron beam as an illumination source to image on a fluorescent screen through the transmission or reflection of electron flow on a sample and the multi-stage magnification of electromagnetic lenses. Optical microscope is an optical instrument that uses visible light illumination to form magnified images of small objects.
1. Different imaging principles
In an electron microscope, the electron beam acting on the sample being tested is magnified by an electromagnetic lens and then imaged on a screen or on photographic film. The mechanism of different electron intensities is that when the electron beam acts on the sample to be tested, the incident electrons collide with the atoms of the substance and scatter. The object image of the sample in an optical microscope is presented by the difference in brightness, which is caused by the difference in light absorbed by different structures of the tested sample.
2. The preparation methods of the samples used vary
The preparation process of tissue and cell specimens for electron microscopy observation is complex, technically difficult, and expensive. Special reagents and operations are required in the steps of material extraction, fixation, dehydration, and embedding. Finally, the tissue block needs to be placed into an ultra-thin slicer and cut into ultra-thin specimens with a thickness of 50-100 nm. Specimens observed under an optical microscope are generally placed on glass slides, such as ordinary tissue section specimens, cell smear specimens, tissue pellet specimens, and cell droplet specimens.
3. Different light sources
The illumination source used in electron microscopes is the electron flow emitted by the electron gun. The illumination source of an optical microscope is visible light (sunlight or light). Due to the shorter wavelength of electron flow compared to light waves, the magnification and resolution of electron microscopes are significantly higher than those of optical microscopes.
4. Different lenses
The objective lens used for magnification in an electron microscope is an electromagnetic lens. The objective of an optical microscope is an optical lens made of glass, which is a circular electromagnetic coil that can generate a magnetic field in the central part. There are three sets of electromagnetic lenses in an electron microscope, which are equivalent to the condenser lens, objective lens, and eyepiece lens in the mirror.
