Electron microscope

I have recently been offered to give some bio samples to have images taken through an electron microscope.
I planning to submit some fungi spores but does anyone else have any other suggestions.
I was thinking some sort of pollen but I was curious on what species have not been done before so that there is some sort of step forward.

I have a maximum of roughly 4 or 5 samples I can give.

would pereskiopsis spines be too big to see? i would love to see them under a microscope.

Yeah, I'd love to see some glochids up close and personal. Maybe something nasty like a barbed spine from one of the more vicious species of Opuntiad?

Yeah, I decided to do a series of fungi spores. It's been a bit hard to organise on the facility's end though. I'll let you know how it goes.