Sample processing methods and steps for electron microscopy
Before using a transmission electron microscope to observe biological samples, the samples must be pre-processed. Scientists use different processing methods as different research requirements require.
Fixation: In order to preserve the specimen as much as possible, glutaraldehyde is used to harden the specimen and osmic acid is used to stain the fat.
Cold fixation: The sample is quickly frozen in liquid ethane so that water does not crystallize and instead forms amorphous ice. Samples preserved in this way have less damage, but the contrast of the image is very low.
Dehydration: Use ethanol and acetone to replace water.
Padded: The sample can be divided after being padded.
Segmentation: The sample is cut into thin slices using a diamond blade.
Staining: Heavy atoms such as lead or uranium scatter electrons more strongly than lighter atoms and can therefore be used to increase contrast.
Before using a transmission electron microscope to observe metals, the sample must be
Viruses under an electron microscope
Cutting into very thin slices (about 0.1 mm) and then using electrolytic polishing to continue thinning the metal often ends up forming a hole in the center of the sample where electrons can pass through the very thin metal there. Metals that cannot be electrolytically polished or materials that are non-conductive or have poor conductivity, such as silicon, are generally thinned mechanically and then processed using ion strike. To prevent non-conductive samples from accumulating static electricity in a scanning electron microscope their surfaces must be covered with a conductive layer.
Why do electron microscopes have higher resolution?
As the name suggests, the so-called electron microscope is a microscope that uses electron beams as the illumination source. Since the electron beam can bend under the action of an external magnetic field or electric field, forming a refraction phenomenon similar to that of visible light passing through glass, we can use this physical effect to create a "lens" for the electron beam, thereby developing an electron microscope. The characteristic of a transmission electron microscope (TEM) is that we use electron beams that pass through the sample to image, which is different from a scanning electron microscope (Scanning Electron Microscope, SEM). Since the wavelength of electron waves is much smaller than the wavelength of visible light (the wavelength of 100kV electron waves is 0.0037nm, while the wavelength of violet light is 400nm), according to optical theory, we can expect that the resolving power of electron microscopes should be much better than that of optical microscopes. In fact, the resolution capability of modern electron microscopes has reached 0.1nm. The elective textbook on physics for senior high school students explains it in more detail (small information behind the photoelectric effect)
