It is believed that the father-and-son tandem of Hans and Zacharias Jansen created, in 1595, the prototype of what is to be the modern compound microscope, using several eyeglass lenses inserted into a tube. Anton van Leeuwenhoek, on the other hand, is considered a pioneer of microscopy, when he began grinding and polishing different lenses, which led to the discovery that certain shapes of lenses increase an image’s size.
Modern microscopes have come a long way from simple tubes and lenses. The classic versions of microscopes have simple wheels and knobs to control the focus of the lenses or the height of the stage; these days, microscopes are typically outfitted with precision z focusing stage and motorized components for better control and magnification detail. These are extremely important when it comes to more precise viewing, imaging, and analysis. Even the “old school” optical microscopes are now becoming digital, employing computer screens instead of eyepieces so that users can view the resulting images.
Microscopes today are especially valuable in the field of microbiology and medicine. They are typically used in understanding how different microorganisms function and interact with their hosts, environment, and even other microorganisms. Depending on the job to be done, microbiologists use different types of microscopes to retrieve different amounts and levels of detail about their specimens.
Electron microscopes use electron beams to generate an image. Due to the shorter wavelengths of electron beams compared to the light output from a bulb or laser, the images from electron microscopes contain much more detail. The two main types of an electron microscope are the scanning electron microscope (SEM) and transmission electron microscope (TEM).
With a SEM, the electrons bounce off the sample to create an image. This is why the specimens are usually coated with a thin layer of gold, palladium, or other highly conductive materials when a SEM is used. A TEM, on the other hand, sends a beam of electrons through very thin specimens, producing a highly detailed, two-dimensional interior image of the subject. The level of detail from a TEM makes it valuable for medical and nanotechnology research.
Electron microscopes do tend to be more demanding in terms of maintenance, but the level of detail from SEMs and TEMs are unmatched.
As the name suggests, X-ray microscopes use X-rays to create an image. They are even capable of determining the individual placement of atoms within crystal molecules. X-ray microscopes can also produce extremely detailed, three-dimensional images of objects, including living cells in their natural state, making these instruments highly valuable in biological research.
Scanning Probe Microscope
A scanning probe microscope or SPM performs raster scanning. The tip of the probe goes line by line to scan the specimen, then the image is generated using a computer. It can go rather slowly, especially with larger specimens, though with the right probe tip, the desired image resolution can be achieved efficiently.
SPMs have two scanning modes: contact and tapping. In contact mode, the force between the probe tip and the surface is kept constant, allowing the user to quickly image the specimen on the stage. In tapping mode, the cantilever oscillates so that the probe tip intermittently touches the surface, which is especially useful for soft, sensitive specimens.
Also called fluorescent microscope, this instrument is valuable in bacteriology and similar fields. Fluorescent microscopes use UV light as its light source; when the UV light hits the specimen, it excites the electrons within, which makes the specimen emit light in various colors depending on its components. Unlike other microscopes, this type uses a confocal pinhole to show the specimen, which shuts out external fluorescent light, thus increasing the resolution of the image.
Also called light microscopes, optical microscopes have the oldest and simplest designs and make use of visible light and lenses to magnify the specimen placed on the stage. They are your “every day” microscopes, used in analyzing a wide array of specimens ranging from blood samples to rocks.
The three most common types of optical microscopes are (1) compound microscopes, which are built with a single eyepiece and a light source underneath the stage; (2) stereo microscopes, which have two eyepieces for the production of a three-dimensional image of the specimen being magnified; stereo microscopes also have light sources above rather than below the stage; and (3) confocal microscopes, which use lasers as a light source to scan the sample with the aid of scanning mirrors; the resulting three-dimensional image is then composed and displayed through a computer. Because a laser light can penetrate a specimen deeper than the traditional light bulb, the images from a confocal microscope are more detailed.
Microscopes operate on the simple premise of magnifying an object’s image. However, these images can help us understand and discover more of the world and make huge scientific leaps, especially in microbiology, health, and medicine.