This is a single speck of dust, viewed at 14,000x under an electron microscope. It’s small enough that it would fit easily inside one of your cells. My lab builds most of our nanostructures in cleanrooms, designed to keep out dust like this… compared to the size of the structures we’re making, like those at the back of the picture, dust is huge. A little bit of dust is hard to avoid, though, and one has to sometimes just hope that the dust doesn’t land somewhere unfortunate. In the case of the picture above, the dust is sitting harmlessly at a safe distance from the nanostructures, as if to guard them - go, nanobulldog!