ananyo writes "DNA origami, a technique for making structures from DNA, has been used to build devices that can seek out and potentially destroy cancer cells. The nanorobots use a similar system to cells in the immune system to engage with receptors on the outside of cells. The barrel-shaped devices, each about 35 nanometers in diameter, contain 12 sites on the inside for attaching payload molecules and two positions on the outside for attaching aptamers, short nucleotide strands with special sequences for recognizing molecules on the target cell (abstract). The aptamers act as clasps: once both have found their target, they spring open the device to release the payload. The researchers tested six combinations of aptamer locks, each of which were designed to target different types of cancer cells in culture. Those designed to hit a leukemia cell could pick that cell out of a mixture of cell types, then release their payload — in this case, an antibody — to stop the cells from growing. The researchers designed the structure of the nanorobots using open-source software, called Cadnano."