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It seems like all the new advances in molecular imaging/microscopy are in the visible light range of the EM spectrum. An example would be the most recent Nobel Prize for Chemistry.

Is there some reason we are only looking for things in the visible part of the EM spectrum? I'd love to know why, and also what techniques look outside of this range?

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  • $\begingroup$ I can not access the link! $\endgroup$ – Freddy Oct 13 '14 at 4:38
  • $\begingroup$ This question is fine here, thanks for bringing up this accomplishment. $\endgroup$ – jonsca Oct 13 '14 at 11:09
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As far as fluorophores go, if the excitation wavelength is too short (< 350 nm), the incident light will get stuck in the microscope. Near-infrared fluorophores, on the other hand, suffer from several drawbacks, especially low quantum yields from competing non-radiative processes.

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    $\begingroup$ Indeed, finding good near-IR emitters is an active area of research. $\endgroup$ – Geoff Hutchison Oct 13 '14 at 2:44
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The reason is not in the technology, the reason is in the application.

There are already electron microscopes which have better resolution for much smaller structures. But, for them, you have to kill and fix your specimen. But the hottest area of application of STED is biology. And there, the coolest thing is to get towards imaging in a live cell, so you can observe the biological processes as they happen.

While you could use wavelengths outside of visible light, they disrupt the processes in the living cell a lot. In fact, the intensity of light needed for these super resolution microscopies is so high that phototoxicity becomes quite a concern in everyday research.

And then you also need fluorescent tissue for these methods. We don't have that many ways to produce fluorescent tissue yet, and the ones we have (mainly GFP) have their peaks in the visible spectrum.

The stuff you can do with this technology is amazing. I recently attended a lecture given by Hell (one of the Nobel winners) and he showed a video of recording the electric impulses in the dendritic cells of an anesthesized mouse. It was haunting - beautiful, but also slightly unnerving, to see inside a live brain. This is why we need the light microscopy - our understanding of life itself depends on it.

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You can do microscopy with other light sources, too. Actually there are X-ray, Raman and IR microscopes, but there are some issues:

  • Few or No lenses: it is difficult(not impossible) to focus IR, UV or X-ray
  • Fewer "light source": in visible region, we have already developed a lot of lasers etc, for UV or X-ray we have fewer options. Part of the reason is that no one needed them, so less effort were put to develop them. Also, high intensity, coherent X-ray sources tend to be synchrotrons or free electron lasers which are marvelous things, but very expensive and big.
  • Less spectroscopic info: Most characteristic optical properties of organic / bioinorganic materials are in the UV-Vis region. In X-ray region generally we have either high energy electric excitation kicking off valence electrons (XPS-UPS) or excitation of core-electrons. Off course, it is not always the case, for example IR or Raman microscopy can be very informative from chemical point of view.
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    $\begingroup$ Also, Kurt Wüthrich got the prize ten years ago for protein NMR and Fenn/Tanaka the same year for making things fly that really refuse to fly. Rod McKinnon got it the year after for crystallizing membrane proteins. It was about time that the visible region got recognized. $\endgroup$ – Abel Friedman Oct 14 '14 at 2:30

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