Special slide + reconstruction algorithm = super resolution microscopy

[rjlittlefield]

This Interesting article appeared in my newsfeed today.

https://phys.org/news/2021-06-light-shrinking-material-ordinary-microscope-super.html

Light-shrinking material lets ordinary microscope see in super resolution

...improves the resolution of an ordinary light microscope so that it can be used to directly observe finer structures and details in living cells.

"This material converts low resolution light to high resolution light," said Zhaowei Liu, a professor of electrical and computer engineering at UC San Diego. "It's very simple and easy to use. Just place a sample on the material, then put the whole thing under a normal microscope—no fancy modification needed."
...
The technology turns a conventional light microscope into what's called a super-resolution microscope. It involves a specially engineered material that shortens the wavelength of light as it illuminates the sample—this shrunken light is what essentially enables the microscope to image in higher resolution.

The technology consists of a microscope slide that's coated with a type of light-shrinking material called a hyperbolic metamaterial. It is made up of nanometers-thin alternating layers of silver and silica glass. As light passes through, its wavelengths shorten and scatter to generate a series of random high-resolution speckled patterns. When a sample is mounted on the slide, it gets illuminated in different ways by this series of speckled light patterns. This creates a series of low resolution images, which are all captured and then pieced together by a reconstruction algorithm to produce a high resolution image.

--Rik

[iconoclastica]

their paper in Nature Communications.

[rjlittlefield]

Excellent! The paper is even "open access", not behind a paywall.

--Rik

[Beatsy]

This is amazing stuff. Assuming the images are a true representation at that scale, the results are fantastic.
They used relatively low-NA objectives (50/0.8 and 40/0.6). Perhaps the scale of the nano-pattern limits that? Dunno.
Assuming that wasn't an issue, would there be *as much* improvement if the images were captured higher NA objectives? I.e. past what's seen as the ultimate, physical limits? I doubt it. But...

[rjlittlefield]

Assuming the images are a true representation at that scale, the results are fantastic.

For me the most convincing evidence of accuracy are the images in Figures 4b-4g, comparing their reconstruction with SEM images of the same bead pattern. I expect that isolated point emitters are the simplest possible case, so that particular comparison does not guarantee that more complicated subjects are also rendered accurately. But the technique sure looks promising so far.

would there be *as much* improvement if the images were captured higher NA objectives?

I expect not. But NA 0.8 is within 2X of the highest NA you could possibly get, and their margin of improvement is quite a bit larger than that.

--Rik

[patta]

Nice, another trick to cheat with the laws of physics! The base method should work also for complicated subjects, not only small beads (but only very near to the slide surface). It is essentially a nano-scanning.
This "random nanospeckle illumination" may be implemented at home, just coat a slide with fine powder, like fine sandpaper (and take 10^6 images, and write the software to process them...)
Standard structured illumination gives 1.4 -2x more resolution than diffraction limit; while other methods currently used in biology research, like single-particle-pinpointing, can go much more, with no hard limit; main practical limit is how many photos you are willing to stack (while the specimen get roasted under heavy laser illumination). And the objective has to be good! I think current top commercial fluorescence systems can consistently take images with like 60 nanometer resolution, 4 times better than the diffraction limit.
The selling points of this (light-shrinking?) method are that it is scanning many "speckle points" at the same time, so it reduces the number of shots needed for a full scan; also it does not need fluorescence.

Giorgio

[MarkSturtevant]

That is interesting, though well beyond my pay grade for following very closely.

EDIT: If I follow -- but only vaguely - the layered material reminds me of how structural colors are made, such as the metallic colors you see on some insects. White light goes in, gets bounced around in a labyrinthine structure, and the reflected colors that are come out mainly a specific wavelength (often blue). So if understood, what happens here is that the colors that come out of the layered material are of shorter wavelength and that is what illuminates the specimen.
I was wondering about the physics of how the light acquires energy, being of a shorter wavelength, but that is maybe not such a mystery.

[Beatsy]

Amplitude is part of the energy equation, and reduced. I think.

[rjlittlefield]

If I follow -- but only vaguely - the layered material reminds me of how structural colors are made, such as the metallic colors you see on some insects. White light goes in, gets bounced around in a labyrinthine structure, and the reflected colors that are come out mainly a specific wavelength (often blue). So if understood, what happens here is that the colors that come out of the layered material are of shorter wavelength and that is what illuminates the specimen.
I was wondering about the physics of how the light acquires energy, being of a shorter wavelength, but that is maybe not such a mystery.

My take is that the brief article at phys.org plays a bit fast and loose with the term "wavelength".

From reading the original article, my understanding is that light of some particular wavelength goes in, and light of that same wavelength comes out, but the spatial pattern of places where that light comes out is a speckle pattern that varies over a much finer scale than the light's wavelength. As a crude analogy, imagine shining light on a thin plate containing a random array of tiny pinholes, each pinhole being a small fraction of the light's wavelength. Most of the energy would never get through the plate at all, but what did get through would emerge entirely from the pinholes. From a distance, in the "far field" where the usual rules of diffraction-limited resolution apply, the plate would look like a dark neutral density filter. But very close to the plate, in its "near field", the pattern of pinholes would remain evident.

What these guys are doing with their fancy slide is to arrange for the light to emerge from the slide in a dense random array of bright spots, very much like a dense random array of pinholes but with no energy loss -- whatever energy fails to emerge from a dark spot of the speckle pattern simply emerges from some bright spot instead.

So, each individual photon coming out has the same energy as each individual photon going in. It's just that the coherence of the incoming photons, interacting with the special structure of the slide, causes the photons to come out in a very fine scale pattern.

--Rik

[patta]

Fully agree, the "array of small pinholes" is a very clean explanation of what's happening. And it is an old trick.
Then you use those pinholes to scan the image near the slide. Resolution will depend on the size of pinholes and how many scanning positions you're taking - not on the light wavelength.

In the paper in question, they've fabricated one "pinhole slide" a little bit better or cheaper than others, or with some more smaller pinholes.
If 've understood correctly, it is made really like a blue butterfly wing scale; but with small picks and imperfections in the layers, that let the light escape, like from small pinholes.
Or, the same, they've taken a dielectric mirror that didn't pass QC because of too many defects; look, it's full of small holes, let's try to use it as pinholes slide. (it is not exactly a dielectric mirror, but a stack of conductor-dielectric; not far away). Clever, actually. Not trivial how the light gets out through the small defects of the mirror; and big job in writing the image processing software to stack all the pinhole images.

But then, the pervert mechanisms of research funding and sensationalist journalism chimed in.
The actual, modest "defective mirror" has been remarketed as a magic and revolutionary "light shrinking material". It worked, and pitched our attention.
Nature Communications! They employ salesman, not editors.

Anyway, one real lesson learned: don't throw away foggy mirrors; they may be very interesting under the microscope.

[MarkSturtevant]

That is very clarifying, thank you all.
Sensationalized science journalism is definitely a problem!