In exemplary implementations of this invention, hierarchical, nanometer-precise assembly is performed: A first structural unit is attached to a solid substrate in a first fluidic flow. A second structural unit is attached to the first structural unit in a second fluidic flow, a third structural unit is attached to the second structural unit in a third fluidic flow, and so on, until a target structure comprising the structural units is assembled. The first, second, third and so on fluidic flows are separate and occur in order in a temporal sequence. During the temporal sequence, a specific permutation of nucleobases is used repeatedly, in separate fluidic flows which occur at different times, to form multiple attachments between structural units in an assembly. The assembled target structure is removed from the solid substrate. Attachments between the structural units may be formed by nucleobase pairing.