A tribute to microscopes and their developers
One of the things kids love the most during science classes is to observe the invisible unraveling through the eyepieces of a microscope. Bacteria flowing in a Petri dish, organelles and filaments swirling in a cell, whatever it is, being able to grasp the mysteries of the invisible equates expert scientist, science lovers, and kids.
When I started my Ph.D., I was certainly excited about the possibility of using microscopes to dig out the mysteries of cellular structures. Yet, while receiving training for different types of microscopes, it never occurred to me how amazingly these machines have evolved over the centuries. Pushed by an unquenchable thirst for knowledge, scientists had to come up with better and better ways to defeat the limit of the invisible. Considered how underestimated the steps of antecedent microscopists often are, not far from the saddening loss of one of the greatest innovators in light microscopy of our times (Shinya Inoué), I want here to retrace few milestones in microscopy evolution.
In chronology:
1st century AD: magnifying lenses already existed at the time of the Roman Empire, but they improved for experiment purposes only in the late 16th century and beginning of 17th century.
1590-1700: microscopes used glass lenses to magnify specimens. Generally, scopes would be composed of one or two lenses but retained a very limited observation resolution due to the spherical aberration of lenses.
1590: the Dutch Zacharias Jansen and his father Hans Lippershey noticed that by placing two lenses at the opposite end of a tube they could greatly enlarge specimens, in comparison to magnifying lenses.
1660: the English Robert Hooke used a two-lenses microscope to observe plant leaves. For the first time, he described the leaf organization as the ordered rows of monk cells in a monastery.
1675: in the Netherland Anthony Leeuwenhoek, while working with magnifying glasses, discovered that polishing and grinding could reduce the lens size and increase its curvature, which allowed him to improve one image resolution. He then built a single-lens microscope to observe blood cells as well as bacteria and from his own saliva and water drops.
1830-1900: Due to the spherical aberration of lenses, scientists struggled in improving the magnifying power of microscopes and continued to use mostly one-lens microscope to conduct their studies. It is only in the 19th century that great discoveries bettered the microscopes, making them smaller and more stable.
1893: the German August Kohler, while working in the Carl Zeiss corporation, was able to sharpen the contrast of an image, and eliminate glare and artifacts by generating an even illumination of the sample;
In Germany, Ernst Leitz built a rotating turret with lenses of different magnifying power;
1870: Ernst Karl Abbe, cofounder of Carl Zeiss AG contributed significantly to remove both spherical and chromatic aberration, and he defined the resolution limit formula of the microscope, as dependent on numerical aperture and wavelength.
1900-present times: we now entered the “modern era” of the microscope:
1930: Ernst Ruska and Max Knoll constructed the electron microscope, capable to reach the resolution of a few nanometers;
In the early 1950s: Shinya Inoué contributed to the development of the polarized light microscopy technique, enabling cell biologists to look at cells without destroying them;
1978: Thomas and Christoph Cremer developed the first confocal laser scanning microscope, for resolution up to 200nm of fluorescence emitting molecules;
1982: Gerd Binnig and Heinrich Rohrer created the Atomic force microscopy (AFM) to measure mechanical properties of molecules, cells, and tissues at a nanometer level;
21th century: Here, we witnessed the discovery of superresolution techniques, which allow us to explore molecules beyond the Abbe’s resolution limit (about 10nm).
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