Eunice can be programmed to recognize specific proteins expressed on the surface of cells. Any cells, actually, but she is usually directed at cancer cells. What is interesting about Eunice is that when she binds to the protein in question, her conformation shifts and she "injects" RNA into the cell. This RNA codes for a protein that poisons the mitochondria of the cell. The mitochondria is the powerhouse of the cell and the cell cannot function without it. Actually, I have billions of sisters named Eunice. When injected into the bloodstream of a cancer patient, she can effectively cure the cancer. She can only inject the RNA after she is bound to the protein. By programming her to bind only to proteins expressed on the surface of the cancer cell, she only affects cancer cells.
Eunice is usually used in combination with Alice. Alice basically does the same thing, but is programmed to recognize a different protein in the same cancer cells. She injects protein that irreversibly binds to the nuclear DNA material, preventing transcription.
Eunice and Alice are used together to prevent the survival of any cells that don't manifest one or the other proteins. Unlikely, but why take chances?
Frieda, another sister, is the golden child. Seriously, she carries nanoshells. These are miniscule beads coated with gold. These can be designed to absorb specific wavelengths of light, including near-infrared light, which can easily penetrate several centimeters of human tissue. The absorption of light by the Frieda creates an intense heat that is lethal to cells.
Did I mention Milton? He is my brother. Milton is one of my favorites. He is sort of like a "bone-glue." When injected into the fracture hematoma, he and his millions of "twins" bind together forming a lattice between the fracture fragments. Within hours, the lattice approximates natural bone strength, allowing full use. Over time, the osteoclasts fill in the lattice.
But my absolute favorite is my little brother Lester. He is a respirocyte. He is a bloodborne spherical 1-micron diamondoid 1000-atm pressure vessel with active pumping powered by endogenous serum glucose, able to deliver 236 times more oxygen to the tissues than natural red cells and to manage carbonic acidity. Release of oxygen is managed by an onboard nanocomputer and numerous chemical and pressure sensors. Obviously, he would function well as a transfusable blood substitute. Imagine, someone with Lester onboard could run full speed for 15 minutes without breathing, or sit on the bottom of a pool for hours.
Maria, another sister, is a silicon-based microcapsule containing pancreatic islet cells. Now most people who receive a pancreas transplant have to be on multiple immune suppressive drugs, with all the attendant complications. Maria is a way around this. She has multiple "nanopores." Now small molecules such as oxygen and glucose can enter, and insulin can exit, but larger molecules such as immune complexes cannot enter. Millions of Marias are implanted beneath the skin of the diabetic patient, allowing natural glucose control functioning without the need for immune suppression.
I am relatively simple, myself. I am used to treat hemachromatosis, or iron overload. I am injected into the bloodstream and I bind iron. After binding, my structure shifts, allowing me to be filtered by the kidneys, taking with the iron. I have numerous relatives that are used as therapy for various toxic ingestions. An emergency room keeps these programmable nanobots handy and programs them for whatever toxic ingestion presents. No more of that nasty n-acetyl cysteine!
The first step to discovering/inventing something is to imagine it and believe that it is possible. This is often the most difficult step, but can be the most fun.