Sunset moth: can we detect the microstructure of the ribs ?

[Lou Jost]

In a post by Beatsy, reader Anne posted some SEM images of the nanostructure of Urania moth scales, including detailed images of the ribs. See them here:
https://www.photomacrography.net/forum/ ... highlight=

Edit: In light of the comments below, I should emphasize that I am NOT talking about the visibility of ribs or crossribs. I'm talking about the layered submicron structure of an individual rib. See the SEMs in Beatsy's post. I've edited the title to reflect this.

So I went looking at some of my sunset moth images to see if the fine structure of the lengthwise ribs on the scales can be detected in any of them. To my surprise, the answer seems to be "maybe yes", though just at the border of detectability in these images. I think with a high-NA oil immersion objective, these structures might be clearly visible, especially if violet light was used.

Here is a 100% crop of my image, enlarged to 200%, taken with a 50x 0.90 finite PlanApo Nikon on a TC14E 1.4x teleconverter on the Panasonic S1R, using unpolarized epi lighting:



Here is the whole image:


Here's another crop of one of my images showing what looks like hints of the rib nanostructure:

[Lou Jost]

Based on my image, I calculate that the long stairstep-like structures in the top of the ribs have lengths 1.2 microns long. This matches the length of the structures on the SEM images.

[Adalbert]

Hello Lou,

I have noticed up to now that the visibility of the microstructure of the scales depends on the aperture and illumination.

e.g.
Oly 80x / 0.75
https://www.photomacrography.net/forum/ ... 99&start=0

Mitty 50x / 0.55
https://www.photomacrography.net/forum/ ... highlight=

BR, ADi

[sushidelic]

I did an epi fluorescence image of the iridescent scales. This is done with blue excitation, an PlanApoN 60x/1.42 oil, specimen was mounted in immersion oil. I was trying out different techniques, this returned the highest resolution.



I have a bunch of different pictures from this session, with different scale types of Urania. This one is the most interesting one, showing the ultra thin cross connections between the "lines". Resolving dots on an Amphipleura is easy in comparison.

Best regards,
Michael

[Lou Jost]

Sushidelic and Adalbert,
I am not talking about resolving the ribs or cross-ribs though. I am talking about resolving the nanostriucture of an individual rib. The ribs are made up of angled layers of material forming little 1.2 micron shelves; see the SEMS in Beatsy's post. That structure is what I am beginning to resolve. These are an order of magnitude smaller than the ribs themselves in the photos you've posted. The view you've posted here, Sushidelic, does not show the 1.2 micron shelves or layering on each rib, each shelf overlapping the next, so that from the top, the rib should look segmented (and each segment should be 1.2 microns long) . Maybe at greater enlargement we could see those structures on your images? Your images should show that, since your NA is so high. The fact that you are resolving the cross-ribs suggests the little shelves on the main ribs should also be resolved.

[sushidelic]

Hey Lou,

here's the full image scaled down:



and here's a link to the full res:

https://imgur.com/a/h9ZZM8V

Full res scale is 20nm per pixel.

You see some irregularity, but I cannot discern the really cool structure, that can be seen in the SEM images.
Also note, that there are some "round" structires in those ribs, that's where I'm hitting diffraction limit.
Maybe if I find a way to look "angled" at one of those ribs, I might get a bit closer in resolving some of the structure.

Best regards,
Michael

Best regards,
Michael

[Lou Jost]

Yes, I think a more oblique view would be needed. We need Beatsy's micromanipulating skills to cut one of these scales in half lengthwise and then stand it on its side.

Your image is so sharp that I think you must be able to resolve those "shelves" if the angle was right.

[lothman]

Sushidelic and Adalbert,
I am not talking about resolving the ribs or cross-ribs though. I am talking about resolving the nanostriucture of an individual rib. The ribs are made up of angled layers of material forming little 1.2 micron shelves; see the SEMS in Beatsy's post. That structure is what I am beginning to resolve. These are an order of magnitude smaller than the ribs themselves in the photos you've posted. The view you've posted here, Sushidelic, does not show the 1.2 micron shelves or layering on each rib, each shelf overlapping the next, so that from the top, the rib should look segmented (and each segment should be 1.2 microns long) . Maybe at greater enlargement we could see those structures on your images? Your images should show that, since your NA is so high. The fact that you are resolving the cross-ribs suggests the little shelves on the main ribs should also be resolved.

I think this shows the layer structure of the ribs. Reminds me of some SEM pictures I made for guppy, he was so kind and sent me some pieces of butterfly wings.
https://www.photomacrography.net/forum/ ... ight=scale
But the SEM I used can only BSE so we also see material contrast. But I think the structures we see on scales are due to shape and not due to material.
So beside the reference wafer we should prepare reference scales ;-)