Nov 042014
 
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Microscopy allows for exciting insights into systems and processes that are otherwise invisible to the human eye due to their size. But as always with technology, there are several limitations. One of the most crucial limitation for microscopy is the resolution limit, defining the minimum distance between two objects, at which they still can be identified as separate objects and not as one big blob.

For classical microscopy, the resolution limit is described by the Abbe-Limit and can be approximated by d=λ/2.[1] This means that, when using visible light with a wavelength of typically 400-700 nm, the resolution limit is around 200 nm.

But what if that is not small enough?

Since scientists are, naturally, never satisfied with the current state of knowledge, a lot of effort has been put into the enhancement of the resolution. One very prominent example was awarded this year’s Nobel Prize in Chemistry. By using fluorescent molecules and a special laser it is possible to track single molecules on their way through living cells, allowing for a ten times higher resolution that typical microscopes.[2]

But what if that is not small enough?

The technique of atomic force microscopy works completely without light, by using a very sharp tip to scan over a surface and sample its topology, much like the needle of a vinyl record player. In recent years the progress has allowed this technique for the imaging of molecular structures, as you would see them in chemistry textbooks, resolving hexagonal rings and carbon-hydrogen bonds.[3]

But what if that is still not small enough?

—Robert Lindner

Read more:

[1] C. Cremer, Physik in unserer Zeit, 2011, 42, 21–29.

[2] S. W. Hell, J. Wichmann,  Optics Letters, 1994 19, 780–782.

[3] L. Gross et al., Science, 2009, 325, 1110-1114.

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