Nucleic acid has been used extensively to build nano-sized objects by controlling assembly through design of base pair interactions in oligo-and poly-nucleotides.Complex nano-objects have been obtained by recursive folding of long nucleic acid sequences and the inclusion of alternating double-stranded and single-stranded regions,junctions and helper oligonucleotides.Structural motifs observed in nucleic acid crystal structures have been employed in the design of nano objects.