C. elegans in bright field and dark field


Thanks to an ongoing experiment, the lab is flooded with animals! The animal du jour is everyone’s favorite model organism, the nematode C. elegans.  The trouble with imaging C. elegans under the Foldscope is that they are (1) very small, (2) mostly transparent, and (3) highly mobile (Most of the time. See the video at the end for an example of not-so-elegans swimming). This makes tracking an individual on a glass slide a daunting task. One trick to increasing the contrast of transparent organisms is using dark-field microscopy. I used a method described in a previous post (https://microcosmos.foldscope.com/?p=7042) to achieve this. As this is my first pass at this technique, this post serves as evidence of my trials and tribulations. The image above distinctly shows the difference between an image taken in bright field (top) and dark field (bottom). It was much easier to locate C. elegans on the slide in dark field, as its features exhibited much greater contrast. The image below is… somewhere in the middle of the previous two, although it was an attempt at dark field. I’m guessing I needed to make ink dot on the tape much darker to obtain a stereotypical dark-field image, although the specimen’s features do contrast nicely. Tomorrow will be another day to refine this technique… more to come.

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UPDATE: Turns out you can get much, much better dark field results with a paper aperture.

dark field aperture

I cut this piece on the laser cutter, leaving the middle piece attached by 3 thin strips. I usually shy away from superlatives, but the resultant images absolutely blew my mind. Even after dozens upon dozens of Foldscoping, I haven’t even begun to scratch the surface of this tool’s potential! For videos of dark field in action, see below.






7 Comments Add yours

  1. laksiyer says:

    Gorgeous. I need to get my dark field set up.

  2. laksiyer says:

    Tom. Any more tips or explorations on the ink used for the black dot would be great.

  3. Tom Hata says:

    Laks, I used a sharpie, but I think I can do better (plenty of light gets through). I’m going to cut out a piece for the light module where the aperture in the paper isn’t completely cut out.

  4. Tom Hata says:

    Laks, please check out the update. Cutting out a paper aperture is definitely the way to go. I can even mail you the aperture if need be. I think I’m going to take a new look at all my samples again tonight!

  5. laksiyer says:

    Tom, the pictures look absolutely gorgeous. True dark field. I used to make such for the compound microscope but for the foldscope it will be a good challenge will try but if you can post it will be great. Cant wait to get to the foldscope.

  6. Manu Prakash says:

    @Laks: we can ship you some of the ark field apertures.

    @tom: please make 20-30 dark field apertures and send to a few active users that request the same. Also; make a cross section drawing of where you put the dark field aperture. It’s crucial for people to see the cross section image since the plane your aperture is put is as crucial as the size of the aperture.

    Welcome all to the dark side 🙂

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