An article on understanding the differences between electron microscopes and optical microscopes
Nowadays, not only are there optical microscopes that can magnify by thousands of times, but also electron microscopes that can magnify by hundreds of thousands of times, allowing us to have a deeper understanding of the laws of biological activities. The vast majority of experiments specified in the biology teaching syllabus of ordinary high schools are completed using microscopes, so the performance of microscopes is the key to observing experiments well.
Microscope is a precision optical instrument with a history of over 300 years. Since the advent of the microscope, people have seen many tiny organisms that were previously invisible, as well as the basic unit of biology: cells
What is an optical microscope:
Optical microscope is an optical instrument that uses optical principles to magnify and image small objects that cannot be distinguished by the human eye, allowing people to extract microstructure information.
What is an electron microscope:
Electron microscope is a large instrument that uses an electron beam as an illumination light source to image on a fluorescent screen through the transmission or reflection of electron flow on the sample and the multi-level amplification of electromagnetic lenses. And an 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 applied to photographic film. The mechanism of different electron intensities is that when the electron beam acts on the test sample, the incident electron collides with the atoms of the material and scatters. The object image of the sample in the optical microscope is presented by the brightness difference, which is caused by the difference in light absorbed by different structures of the tested sample.
2. The preparation methods of the samples used are different
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 blocks need to be placed in 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 a glass slide, such as ordinary tissue section specimens, cell smear specimens, tissue compression specimens, and cell drop specimens.
3. Different light sources
The lighting 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 wave, the magnification and resolution of electron microscopy are significantly higher than those of optical microscopy.
4. Different lenses
The objective lens that plays a magnifying role 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, objective, and eyepiece in the mirror.
