Two dimensional PNA/DNA arrays: estimating the helicity of unusual nucleic acid polymersElectronic supplementary information (ESI) available: sequence data, experimental protocols for assembly of the tiles and arrays and gel electrophoresis data demonstrating formation of the tiles. See http://www.rsc.org/suppdata/cc/b4/b401103a/

We extend the generality of nucleic acid-based structural nanotechnology by incorporating non-natural nucleic acids into a DNA double crossover (DX) molecule; visualizing two-dimensional arrays of these DX molecules by Atomic Force Microscopy (AFM) enables us to measure the helical repeat of any heteroduplex sequence capable of forming the outer arms of a DX.