Slidewich Tek: An agar plate that's also a microscope slide

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Rasmodius
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Registered: 05/03/26
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Slidewich Tek: An agar plate that's also a microscope slide

11
#29677064 - 09/24/26 07:38 AM (26 days, 4 hours ago)

What is the slimmest functional agar plate possible? This is me attempting to find out.

I want to inspect my agar plates under the microscope at large magnifications, which requires getting very close. Far closer than a normal petri dish would let you. Flipping the plate upside down is a tough sell at 1000x. Even with crystal clear agar poured paper thin, the plastic/glass alone eats through the whole focal length, and the agar way more.

This is why people press slices of agar into microscope slides, or put cover glass directly on top of open plate contents. Both of these work well enough, but compromise the sterility of the sample (or the whole plate), unless you bring a whole ass microscope into the flow hood and clean it extremely well.

:getstoned:

What if you had something that could stay sealed like a petri dish yet was as observable as a covered slide?

This is The Slidewich.

It uses RTV silicone (same as jar lids) to make a short wall, sandwiched between a slide for the floor and cover glass as a lid. You can pour and grow inside of it like a petri dish, but the entire assembly is under 4mm tall, and the distance between the outer surface and the agar can be under 1mm. This makes it suitable for use with high magnification.

Ingredients

RTV silicone, tween20, slides, and cover glass. Plus normal PC and agar materials.

I got wider-than-usual cover glass for this, 50mm wide x 24mm tall. That's still shorter than the full slide glass. You can see them overlayed here.

RTV is high temp gasket maker, making a semiflexible seal between two surfaces is its job. With the cover underneath as a reference, use a slip-tip syringe body to apply as orderly a bead of RTV as possible in a shape smaller than the cover glass.

Tip: To get the RTV in the syringe, pull the back of the syringe out, squeeze the silicone inside, and then use the plunger to push it forward. This cuts down on the smell and makes it much easier to direct. This is also how I get my jar lid injection ports so crispy.

We want to create a smooth, even surface for the cover glass to stick onto, but we don't want to glue it in place. So we need a release agent, something nonstick-ish. I already had tween20 because of this great spore revival tek. I also tried straight up lube (if it's good enough for my dick it's good enough for my celium, amirite), but that didn't work as well JSYK. There are probably better chemicals for this, LMK if you know of any that are myc-safe.

Using a paper towel or similar, butter one side the cover glass.

Press it down until the gasket has enough contact area for your liking. Let the whole thing dry for about 24 hours, and peel the lid off. You can use a scalpel blade to pry underneath a bit and get it started. The silicone is tough and somewhat self-healing if lightly cut. A bit of RTV stayed on the cover glass, I just tossed it and used a fresh one for the lid.

Wash the tween20/polysorbate off. Fill another syringe body with agar mix and wrap in foil. Using foil or a jar, wrap the cover glass and slides. PC/IP for 30 minutes. This will keep them dry and away from dirty air until they're in the hood/SAB, at which point you can open them.

Using the syringe, "pour" the plates with a very thin layer of agar. This is standard 500/10/10 LMEA mix, but I don't like the consistency here, the surface could be more even. Prefer underfilling to overfilling so it doesn't hit the lid.

After the agar cools (which at this size is almost instantly), you can transfer in a tiny slice from another plate, or add spores, whatever. And then press a fresh cover piece back in place.

Because the agar is so thin, I didn't want these to dry out, but you can't exactly parafilm them. So I put them under a lid in the running hood to keep the moving air off them. I gave them a head start in the flow hood to see if they would take, before letting them be in open air for a few days to see if they would contaminate. It's been about a week. So far so good.

Results

Of course there's still condensation lol. But it did work well enough that there's new growth to look at.

And look we shall! Here's 1000x under the oil lens. Those dots are my eye lenses being dirty, not the agar.

Teeeeeeny tiny clamp connections on a strand of dikaryotic mycelium.

:magicfingers:

And that's how you build a functional petri dish under 4mm tall that can do oil magnification. This visibility is on par with a pressed slide.

It is an enormous pain in the ass for a very obscure payoff and I mostly wanted to see if it could be done. I'm going to keep refining the manufacture to see if I can get it to not be so fuckin janky. There are some 1/4" thick polypropylene sheets in the mail, with the hopes that I can CNC some nice rectangles with cutaways for the cover, to have something more polished and durable. 3D printing the part would involve a hardened steel nozzle, heated enclosure, and some fussy/expensive filament (carbon-fiber reinforced polypropylene) so that's only as a last resort. Technically it works as it is, so I'm gonna see if it's actually useful long term before sinking a shitload of time into making it fancy.

Does this work?
Definitely yes

Does this work well?
Definitely no, at least not yet.

This is impractical as all fuck?
That's not a question, but I agree.

Thank you for reading!

Extras:

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