A magnetic lens consists of electromagnets and is utilized in electron microscopes, such as the transmission electron microscope (TEM), to focus the electron beam onto the specimen. This magnetic mechanism replaces the traditional glass lenses used to focus light in optical microscopes.

Magnetic Lens

For a transmission electron microscope (TEM) to function properly, the specimen and the electron beam must be placed in a vacuum. Additionally, the specimen must be fully dehydrated and cut extremely thin, typically between $${}20-100$$ nm thick, to allow the electrons to successfully pass through it.

TEM Specimen Requirements

In transmission electron microscopy (TEM), contrast is artificially enhanced by staining specimens with electron-dense materials containing heavy metal atoms, such as uranyl acetate or osmium tetroxide, rather than colored dyes. Prior to this staining process, the extremely thin sample sections are typically secured to fine copper wire or carbon-fiber grids to support them during observation.

Electron-Dense Staining

The transmission electron microscope (TEM) is a type of electron microscope that functions analogously to a brightfield microscope. It utilizes an electron gun to release an electron beam that is directed from above the specimen and focused using a magnetic lens. The electrons pass through the specimen and are then projected onto a detector to capture the image. TEM is particularly useful for observing small, thin specimens, such as tissue sections and subcellular structures.

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Electron microscopy utilizes short-wavelength electron beams, focused with magnets, to significantly increase magnification and resolution compared to visible light. While light microscopes are limited by visible light wavelengths, electrons behave as waves with much smaller wavelengths, allowing an electron microscope to produce sharp images with magnifications ranging from $${}20	imes$$ to $${}100,000	imes$$ or more. This resolving power enables the visualization of subcellular and molecular structures. However, electron microscopy cannot be used on living material due to the harsh methods required to prepare the specimens prior to viewing.

Electron Microscopy

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Transmission Electron Microscope (TEM)

A scanning electron microscope (SEM) is an instrument that forms highly detailed images of the surfaces of specimens. It operates by directing a beam of electrons at the specimen, which knocks off electrons from its surface. These emitted electrons are detected and displayed on a monitor, producing images with a distinct three-dimensional appearance. Scanning electron microscopy is utilized to view the external surfaces of both very small samples and larger objects, such as pollen grains. Some electron microscopes can achieve magnifications up to $${}2,000,000	imes$$.

Scanning Electron Microscope (SEM)

While electron microscopy can be utilized to view the structures of biofilms, it has significant drawbacks. The preparation process requires dehydrating the specimen, which can distort the biofilm and introduce undesirable artifacts, making it less ideal than techniques like confocal microscopy for observing living microbial communities.

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