This nanobot serves a very specific purpose. This travels through the bloodstream and destroys unwanted clots. It is currently depicted with its scythe-like claws out, but they are retractable. Normally, when it is just traveling around, it is smooth as a bullet, with no sinister blades visible. Here, it is about to preform minor surgery on another unsuspecting clot. As for the green blood - it is obvious that these nanobots are traveling through an alien bloodstream.
Created for my concept art class. We had to create 75 different robots. This is one of mine. Originally I didn't have blood, but then I realized that blood would perfectly complete the image - it gave the nanobot purpose, as well as gave a size reference.
Drawn in pencil, then colored with Photoshop and GiMP.