We introduce the concept and operation of ab inding-induced DNAn anomachine that can be activated by proteins and nucleic acids.T his new type of nanomachine harnesses specific target binding to trigger assembly of separate DNAc omponents that are otherwise unable to spontaneously assemble.T hree-dimensional DNAt racks of high density are constructed on gold nanoparticles functionalizedw ith hundreds of single-stranded oligonucleotides and tens of an affinity ligand. AD NA swing arm, free in solution, is linked to asecond affinity ligand. Binding of atarget molecule to the two ligands brings the swing arm to AuNP and initiates autonomous,stepwise movement of the swing arm around the AuNP surface.T he movemento ft he swing arm, powered by enzymatic cleavage of conjugated oligonucleotides,c leaves hundreds of oligonucleotides in response to as ingle binding event. We demonstrate three nanomachines that are specifically activated by streptavidin, platelet-derived growth factor,a nd the Smallpox gene.S ubstituting the ligands enables the nanomachine to respond to other molecules.The new nanomachines have several unique and advantageous features over DNA nanomachines that rely on DNAs elf-assembly.