The machines are so tiny that 50,000 of them together is still about the width of a single strand of human hair. Each machine is engineered to be sensitive to a protein located on a specific type of cell, which helped them find their target. Once you add light, they spin up to 3 million times per second, and this spinning provides the power needed to break into a cell. Without light, the nanomachines can still find the molecule, but just remain on the surface.
When scientists let these nanomachines loose in a dish full of human kidney cells, the nanomachines made holes in the cells and killed them within minutes. The same thing happened when the nanomachines were unleashed on cancerous prostate cells.