'Want to see a thousand miles, a higher level', human exploration of the microscopic world, just like climbing the peak of knowledge, and the microscope is precisely our look into the microscopic mysteries of the 'clairvoyance'. However, even this magical 'clairvoyance', also has its observation boundary.
Optical microscopes use visible light imaging to clearly render micron-sized objects such as cells, bacteria, parasites, pollen, and so on. For example, in biology class, students can observe the form of human cell nuclei under the optical microscope by staining treatment; the pond water made into a clinical film, but also can directly observe the activities of lacewings.
However, the light microscope has obvious observation limitations. Because the light can not penetrate, metal blocks, wood and other opaque objects are difficult to observe directly, need to be cut into thin slices with a thickness of several tens of microns; at the same time, affected by the fluctuation of light, its resolution is limited, the diameter of less than 200 nanometres of viruses, nano-particles, and other objects, it is difficult to image clearly.
Electron microscopy replaces visible light with an electron beam, and after the beam impacts the sample, the bouncing signal can be converted into an image. Transmission electron microscopy (TEM) can penetrate deep into the sample and clearly show the spiny proteins of the new coronavirus and the mitochondrial structure inside the cell; while scanning electron microscopy (SEM) focuses on the surface of the sample and can meticulously present the nanoscale scales of insect wings and the three-dimensional patterns of plant pollen.
However, electron microscopes need to work in a near-vacuum environment, resulting in the loss of moisture in fresh biological cells, which prevents dynamic observation; and the high energy of the electron beam, fresh fruit slices, moist soil and other watery or volatile samples, easy to be destroyed, and can not be imaged properly.
With the development of technology, new microscope, field microscope, plant microscope keep emerging, these limitations are being gradually broken. As a result, most of the 'inability' of the microscope's observation ability stems from the limitations of the physical principles rather than from the defects of the technology.
