Structured illumination: the Bruce Wayne of the super-resolution league?


A week before Eric Betzig shared the Nobel Prize with Stefan Hell and William Moerner for super-resolution fluorescence microscopy, I listened to him give a talk at an imaging conference in Edinburgh, Scotland. The talk focused on Structured Illumination Microscopy (SIM). The idea that SIM does not belong in the same category as STED and super-localisation techniques, Betzig repeatedly stressed, is ludicrous. Betzig is so convinced of this notion that his group has moved to focus on developing applications of SIM for live imaging.

The best image resolution obtained by SIM is only about twice as good as that imposed by the normal diffraction limit, paling in comparison to the hundred times improvement sometimes seen by STED, but SIM is faster and runs on a more efficient light budget than the rest of the super-resolution stable. This creates non-trivial advantages when the subject is alive and preferred to stay that way. Biologists can learn a lot from studying something which is formerly alive, but much more from cells in the dynamic travails of life.

If Betzig is convinced working with SIM is more amenable to practical application than other super-resolution techniques, such as Photo-Activated Localisation Microscopy, the technique that won him the Nobel Prize, why was it left out when it came time for the Swedish Academy of Sciences to recognise super-resolution? The answer may lie more in the rules and peculiarities surrounding the awarding of a Nobel than on the scientific relevance and impact, but you wouldn’t guess that from reading the Scientific Background on the Nobel Prize in Chemistry 2014.

In the published view of the Kungl Vedenskapsakademien, SIM, “Although stretching Abbe’s limit of resolution,” remains ”confined by its prescriptions.” In other words, the enhancement beyond the diffraction limit achieved by structured illumination is just not super enough. In principle the resolution of STED can be improved without limit by switching your depletion laser from “stun” to “kill” (i.e. increasing the depletion intensity). Likewise, super-localisation is essentially a matter of taking a large number of images of blinking fluorescent tags. Improving the effective resolution in super-localisation is a case of tuning the chemistry of your fluorescence molecules and taking an enormous amount of images. In reality, practical problems prevent further resolution improvement long before the capabilities of these techniques reach the resolution of a Heisenberg’s microscope, for example. However, SIM is subject to an “aliasing limit,” which, for the nonce, seems to be as hard and fast as Abbe’s and Rayleigh’s resolution criteria were (and largely still are, with the exception of fluorescence techniques) for the last hundred years.

As a rule with only one exception I know about, a Nobel Prize is not awarded post-mortem. Despite the justification proffered in the official background, Mats Gustaffson’s untimely death in 2011 may have played a major role in the exclusion of super-resolution structured illumination microscopy. Combined with the cap of three people sharing a single Prize, this left Rainer Heintzmann and the late Mats Gustaffson without Nobel recognition of their contributions to super-resolution. Even with the somewhat arbitrary adjudication over what it is to truly “break” the diffraction limit, it seems curious that one of the super-res laureates has moved almost entirely away from the prize-winning technique he invented, preferring instead the under-appreciated SIM. The Nobel Prize is arguably the penultimate distinction in scientific endeavor, and it seems beneath the station of the prize for its issue to be governed so strictly by arbitrary statutes. Then again, the true reward of scientific achievement is not a piece of gold and a pile of kronor, but the achievement itself. The universe isn’t altered whether you win the Nobel Prize for uncovering one of its little secrets, the truth of the secret will remain regardless.

‘Anonymous’ has an intriguing comment about why super-resolution is still not finding common use in biology research here.

Interesting note: unlike STED and PALM/PAINT/STORM, structured illumination can be applied to quantitative phase imaging

The original version of the bell .svg file is from:

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