He coated the rock in “a special epoxy” to prevent it from crumbling during slicing. Then, he washed the thin sections in a special dye that stained the DNA of the microbial cells.
What does that mean—I thought DNA was smaller that the wavelength of visible light? I guess it’s some larger molecule that binds to the DNA to make it more visible, but if that’s the case, “tagging” seems like a more appropriate term than “staining”.
It’s usually used for something that changes the superficial appearance of a thing without changing or obsuring its structure—and in this context it seems to mean making the DNA more detectable (by whatever means). I’m not picturing how this “dye” could do both those things at once on that scale.