Microscopes are high-tech equipment that enable us to see the world at an entirely different level. What most people don’t know is that the first compound microscope was created in 1590, by Dutch spectacle makers Hans and Zacharias Janssen.
There are many types of microscopes available on the market today, with two of the most common being light microscopes and electron microscopes. It’s crucial to understand what they are and how they are different, to ensure your lab has the right equipment for your needs.
What is a Light Microscope?
A light microscope may also be referred to as an optical microscope. It uses light, at approximately the 400 to 700 nm wavelength to illuminate the objects under view. The lenses are made of glass, and the image is formed by the absorption of light. Light microscopes are lightweight and fairly small. They do not operate under a vacuum.
You can use a variety of specimen types, including fixed or unfixed, stained or unstained, living or dead. It doesn’t take a lot of work to prepare specimens for the microscope. Generally, it can be done within a few minutes to a few hours.
The specimen can be 5 micrometers or thicker, and does not have to be dehydrated before looking at it. The specimen is stained with colored dyes to make it properly visible. The specimen is then mounted on the glass slide, and can be magnified up to 1,500x. That may sound impressive, but it’s on the low-end of what microscopes can do. Focusing the image is done by mechanically adjusting the lens position.
Light microscopes tend to have low resolving power, with a poor surface view. They present flat images in color, but it is possible to see living processes like cell division and microscopic pond life. There are no special settings required for the room where the microscope is housed. Images are viewed directly with the human eye through the eyepiece.
Light microscopes are simple to use and do not require the use of high voltage power or filaments. There is no radiation risk. They are affordably priced and have low maintenance costs.
Types of light microscopes include:
- Dark-field microscopes: Those that block visible light to refract it and make the subject brighter on the background
- Phase-contrast microscopes: Converts phase shifts in light passing through a transparent specimen to change the brightness of the image.
- Fluorescent microscopes: These microscopes use fluorescence and phosphorescence either instead of, or in addition to light reflection and absorption to study specimen properties.
Light Microscope Uses
Light microscopes are well suited to the majority of basic functions, and it is common to see them in schools. Uses include examining:
- Thin bacteria that’s not visible with ordinary illumination
- Mounted cells and tissues
- Marine organisms
- External details such as grain boundaries, outlines, and edges
- Living cells in culture
- Glass fragments
- Thin tissue slices
- Subcellular particles
- Structures in fixed and live biological samples with multicolor staining
What is an Electron Microscope?
An electron microscope is also known as a beam microscope. It was invented in 1931, by physicist Ernst Ruska and engineer Max Knoll. It uses a beam of electrons to make objects larger and present a more detailed picture. The images are formed by the transmission or scattering of electrons. Rather than glass, these feature electromagnetic lenses. They are heavier and larger than light microscopes, and operate under a high vacuum.
With an electron microscope, you cannot observe live specimens. The specimen must be fixed or stained. Preparing the specimen is more labor intensive, generally requires a high skill level, and can take a few days to complete. The process usually requires the use of corrosive chemicals and involves interpreting the images due to artifacts.The specimen is ultra thin – usually 0.1 micrometers or below. This type of microscope only uses dehydrated specimens. Specimens are coated with heavy metals to reflect electrons and are mounted on a metallic grid that is mostly copper. Focusing is done by adjusting the power of the electric current to the lenses.
Electron microscopes have high magnification ability, up to 1,000,000x. They also have high resolving power, about 250x that of a light microscope. The image that’s formed provides a good surface view along with internal details, but forms in grayscale. Rather than being viewed directly by the eyes through an eyepiece, images are viewed on either a zinc sulfate fluorescent screen or a photographic plate.
Unlike with a light microscope, living processes cannot be viewed. In transmission electron microscopy (TEM), you can only view images in 2D. If you use scanning electron microscopy (SEM), depth is added to make it seem like a 3D image.
Electron microscopes have to be used in a highly controlled environment, where pressure, temperature, and humidity are regulated. They also require a high voltage current of at least 50,000 volts, and tungsten filaments. They include a cooling system to reduce the heat generated by the high voltage current. There is a risk of radiation leakage.
These microscopes are highly complex, expensive to purchase, and expensive to maintain. If you require one in your lab, opting for a leasing program like the one offered here at Excedr can help you obtain one for a fraction of the upfront price, making it easier for your budget to go further, and getting you what you need faster than raising capital for a major purchase.
Electron Microscope Uses
Because of the complexity of these machines, electron microscopes are limited to specialized functions, such as research. It is most often used in the study of external structures – the ultrastructure of cells and other very small organisms.
With SEM, a beam of electrons moves back and forth across the surface of the specimen – whether it is tissue or a cell. This creates a detailed 3D image of the surface.
With TEM, the sample is cut into thin slices before it is imaged. In this technique, the electron beams pass through the slice instead of over the surface. This results in detailed images of the internal cell structures.
Light Microscope vs Electron Microscope: Which is Better?
Both light microscopes and electron microscopes have their place in science. The better choice depends on the task at hand and the nature of your research