About the Different Types of Microscopes

Since their inception in 1595 by Dutch eyeglass makers Sacharias Jansen and Hans Lippershey, microscopes have become an integral and continuously evolving instrument in the field of scientific analysis. All microscopes seek to expand and magnify the visual image of a target beyond the ability of the unaided eye. Microscopes can be differentiated by the medium they employ to accomplish magnification: light, an electron beam, sound waves or physically probing the target surface.

The Facts

All microscopes, with the exception of probe microscopes, magnify and generate an image based on the diffraction, reflection and/or refraction of electromagnetic or sound wave radiation. The resolving power of a microscope is limited by radiation diffraction and by the target specimen environment.

Optical Microscopy

Optical or light microscopy magnifies specimens by manipulating electromagnetic radiation, typically within the visible spectrum. Limited to resolving objects in the 200 to 500 nanometer range, optical microscopes are predominantly used in biology for their ability to monitor and image living cells. Dutch Scientist Antoni van Leeuwenhoek's compound microscope was the first to view bacteria in 1676, earning him the honorific "Father of Microscopy." Popular iterations of the optical microscope include the stereoscopic binocular, bright-field illumination, polarizing light, phase contrast, dark field and fluorescence microscopes.

Electron Microscopy

Electron microscopes utilize an electron beam to image a sample. The magnifying power of an electron microscope is derived from an individual electron's wavelength, which allows these microscopes to resolve objects as small as 0.05 nanometers. The first electron microscope, a transmission electron microscope, was invented by Ernst Ruska and Max Knoll in 1931. Transmission electron microscopes, scanning electron microscopes and scanning transmission electron microscopes are the most widely used forms of electron microscopy.

Acoustic Microscopy

Acoustic microscopy uses ultrasound waves, at a frequency of 5 to 400 MHz, to image a sample with micrometer-level resolution. Like light or electrons, the ultrasound waves penetrate a specimen and are then reflected, refracted or diffracted by the sample. The first acoustic microscope was constructed in 1959 by F. Dunn and W.J. Fry. Due to their ability to non-destructively visualize internal characteristics, acoustic microscopes are used extensively in quality control applications and electronic component manufacturing.

Probe Microscopy

With resolution at the atomic level, scanning probe microscopes are the newest and most powerful form of microscope available. Probe microscopes use an extremely small tip, usually only a few atoms in width, to physically touch the surface of a sample and map its shape. The probe tip is attached to a cantilever, which moves up and down in response to the sample's surface features. A laser tracks the minute changes in cantilever position, and computer algorithms reconstruct the surface data into visual images. The first probe microscope, a scanning tunneling microscope, was developed in 1981 by IBM's Gerd Bining and Heinrich Rohrer. Other probe microscopes include the atomic force microscope and specialized iterations of the scanning tunneling microscope.

References

• Nobel Foundation: Microscopes Time Line
• Steve's Place: Electron Microscopy
• Various Types of Optical Microscopes