HISTORY OF MICROSCOPE

 MICROSCOPY

·                  Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye). A microscope is an optical instrument that magnifies objects otherwise too small to be seen, producing an image in which the object appears larger. A microscope uses a lens or a combination of lenses to produce highly magnified images of small specimens or objects especially when they are too small to be seen by the naked eye. A light source is used to make it easier to see the subject matter. Most photographs of cells are taken using a microscope, and these pictures can also be called Micrographs. Three parameters are especially important in microscopy: Magnification, Resolving power and Numerical aperture.

i) Magnification

·       Magnification is a measure of how much larger a microscope (or set of lenses within a microscope) causes an object to appear. For instance, the light microscopes typically used in high schools and colleges magnify up to about 400 times actual size. So, something that was 1 mm wide in real life would be 400 mm wide in the microscope image.

ii) Resolving Power

·                   Resolution is the power to details clearly (Resolution of human eye is 0.2 mm). Resolution (also called resolving power) is the ability of the lenses to distinguish fine detail and structure. Specifically, it refers to the ability of the lenses to distinguish two points a specified distance apart. For example, if a microscope has a resolving power of 0.4 nm, it can distinguish two points if they are at least 0.4 nm apart. A general principle of microscopy is that the shorter the wavelength of light used in the instrument, the greater the resolution.

Resolving Power = Wavelength of light in nm/ 2 × Numerical aperture of the objective lens

iii) Numerical Aperture

·                   Numerical aperture is a number represents the angle of light produced by refraction and is a measure of the quantity of light gathered by the lens. Numerical aperture, a mathematical constant derived from the physical structure of the lens. Each objective lens has a fixed numerical aperture reading ranging from 0.1 in the lowest power lens to approximately 1.25 in the highest power (oil immersion) lens. Lenses with higher Numerical aperture provide better resolving power because they increase the angle of refraction and widen the cone of light entering the lens.

HISTORY OF MICROSCOPE

·       710 BC: The Nimrud lens (a piece of rock crystal) may have been used as a magnifying glass or as a burning-glass to start fires by concentrating sunlight. It is later unearthed by Austen Henry Layard at the Assyrian palace of Nimrud in modern-day Iraq.

·      1000 AD: The first vision aid called a “Reading stone” was invented. It is a glass sphere placed on top of text, which it magnifies to aid readability.

·    1021 AD: Muslim scholar Ibn Al-Haytham writes his “Book of Optics”. It eventually transforms how light and vision are understood.

·       1284 AD: Salvino D’Armate was credited with inventing the first wearable eye glasses.

·       14^th century: First Spectacles was made in Italy.

·       1590: Two Dutch spectacle-makers and father-and-son team, Zacharias Janssen and his son Hans place multiple lenses in a tube. They observe that viewed objects in front of the tube appear greatly enlarged. This is a forerunner of the Compound microscope and the Telescope.

·       1609: Galileo Galilei develops a Compound microscope with a Convex and a Concave lens.

·       1625: Giovanni Faber coins the name ‘Microscope’ for Galileo Galilei’s Compound microscope.

·       1665: English Physicist Robert Hooke published his drawing book “Micrographia”. The book was filled with drawings of hairs on a nettle and the honeycomb structure of cork. He uses a simple, single-lens microscope illuminated by a candle. Robert Hooke was the first person to use the word “cell” when describing living organisms.

·       1676: Anton van Leeuwenhoek (Father of Microscope) builds a Simple microscope with one lens to examine blood, yeast and insects. Leeuwenhoek was the first to observe bacteria. He invents new methods for making lenses that allow for magnifications of up to 270 times.

·       18^th century: As technology improved, microscopy became more popular among scientists. Part of this was due to the discovery that combining two types of glass reduced the chromatic effect.

·       1830: Joseph Jackson Lister reduces spherical aberration (which produces imperfect images) by using several weak lenses together at certain distances to give good magnification without blurring the image.

·       1838: Two Germany scientists, Mathias Schleiden and Theodor Schwann proposed that cells were the building blocks for plant and animal life. They published their findings as the Drawing book in the name of "Mikroskopie".

·  1874: Ernst Abbe writes a mathematical formula that correlates Resolving power to the Wavelength of light. Abbe’s formula makes it possible to calculate the theoretical maximum resolution of a microscope.

·  1877: The first homogeneous Oil immersion Objective lens was developed by John Ware Stephenson.

·      1903: Richard Zsigmondy invents the Ultramicroscope, which allows for observation of specimens below the wavelength of light.

·    1931: Ernst Ruska and Max Knoll design and build the first Transmission Electron Microscope (TEM), based on an idea of Leo Szilard. The electron microscope depends on electrons, not light, to view an object. Modern TEMs can visualise objects as small as the diameter of an atom.

·     1934: Phase Contrast Microscope was first described by Dutch Physicist Frits Zernike for which later in 1953 he was awarded the Nobel Prize in Physics. Transparent biological materials are studied for the first time using the Phase contrast microscope.

·    1938: Just six years after the invention of the Phase contrast microscope comes the Electron microscope, developed by Ernst Ruska, who realized that using electrons in microscopy enhanced resolution.

·       1942: Ernst Ruska builds the first Scanning Electron Microscope (SEM), which transmits a beam of electrons across the surface of a specimen.

·       1957: Marvin Minsky patents the principle of Confocal imaging. Using a scanning point of light, Confocal microscopy gives slightly higher resolution than conventional light microscopy and makes it easier to view ‘virtual slices’ through a thick specimen.

·     1962: Osamu Shimomura, Frank Johnson and Yo Saiga discovered Green Fluorescent Protein (GFP) in the Jellyfish. GFP fluoresces bright green when exposed to blue light.

·       1972: Godfrey Hounsfield and Allan Cormack develop the Computerized Axial Tomography (CAT) scanner. With the help of a computer, the device combines many X-ray images to generate cross-sectional views as well as three-dimensional images of internal organs and structures.

·  1973: John Venables and C. J. Harland observe Electron Backscatter Patterns (EBSP) in the Scanning Electron Microscope. EBSP provide quantitative microstructural information about the crystallographic nature of metals, minerals, semi-conductors and ceramics.

·  1978: Thomas and Christoph Cremer developed the first practical Confocal Laser Scanning Microscope, which scans an object using a focused laser beam.

·    1981: Gerd Binnig and Heinrich Rohrer invent the Scanning Tunnelling Microscope (STM). The STM ‘sees’ by measuring interactions between atoms, rather than by using light or electrons. It can visualize individual atoms within materials. 3D specimen images possible with the invention of the Scanning Tunneling Microscope.

·     1986: The Nobel Prize in Physics is awarded jointly to Ernst Ruska (for his work on the Electron microscope) and to Gerd Binnig and Heinrich Rohrer (for the Scanning tunnelling microscope).

·       1992: Douglas Prasher reports the cloning of Green fluorescent protein (GFP). This opens the way to widespread use of GFP and its derivatives as labels for Fluorescence microscopy (particularly Confocal Laser Scanning Fluorescence Microscopy).

·      1993: Stefan Hell pioneers a new Optical microscope technology that allows the capture of images with a higher resolution. This results in a wide array of high-resolution optical methodologies, collectively termed “Super-Resolution Microscopy”.

·      2008: Richard Henderson attributes the enormous increase in High-resolution Cryogenic Electron Microscopy (Cryo-EM) structures to the introduction of Direct Electron Detectors. These detectors can deal with systematic noise and produce clearer micrographs, making particles easier to classify.

·       2010: Researchers at University of California, Los Angeles (UCLA) use a Cryoelectron microscope to see the atoms of a virus.

2014: Nobel Prize in Chemistry awarded to Eric Betzig, Stefan Hell and William Moerner for the development of Super - Resolved Fluorescence Microscopy which allows microscopes to now ‘see’ matter smaller than 0.2 µm.