What if we took a recursive approach and built a smallest possible first robot (Robot 1) that could transfer information and data about the place it was at and could build itself in a very small size proportional to itself. I understand that it means a higher level of accuracy for this first robot (Robot 1) that its creator i.e. us. And this first robot (Robot 1) again built a robot (Say Robot 2) that was far smaller but an exact copy of the first robot (Robot 1). And then the second robot (Robot 2) built a third Robot (Robot 3) and so on. So each next level robot was tinier and higher precision than its creator.
With the tiniest robot we could make, we sent them to the mission wherein micro-sized intervention was needed. For example studying the atom structure from inside, how similar it was to our big universe etc. Plus many more applications humankind could ever imagine.
I understand though that the material used to construct such a robot and its properties will be limiting and to explore an atom we may not be able to use an atom as the building block.
However, we could possibly build a robot like this which would be small enough to explore the human body from inside.