The aim of nanotechnology is to put specific atomic and molecular species where we want them, when we want them there. Achieving such dynamic and functional control could lead to programmable chemical synthesis and nanoscale systems that are responsive to their environments. Structural DNA nanotechnology offers a powerful route to this goal by combining stable branched DNA motifs' with cohesive ends to produce programmed nanomechanical devices(2) and fixed(3-5) or modified(6,7) patterned lattices. Here, we demonstrate a dynamic form of patterning(8) in which a pattern component is captured between two independently programmed DNA devices. A simple and robust error-correction protocol has been developed that yields programmed targets in all cases. This capture system can lead to dynamic control either on patterns or on programmed elements; this capability enables computation or a change of structural state as a function of information in the surroundings of the system.