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In biological systems and nanoscale assemblies, the self-association of DNA is typically studied and applied in the context of the evolved or directed design of base sequences that give complementary pairing, duplex formation, and specific structural motifs. Here we consider the collective behavior of DNA solutions in the distinctly different regime where DNA base sequences are chosen at random or with varying degrees of randomness. We show that in solutions of completely random sequences, corresponding to a remarkably large number of different molecules, e.g., approximately 10(12) for random 20-mers, complementary still emerges and, for a narrow range of oligomer lengths, produces a subtle hierarchical sequence of structured self-assembly and organization into liquid crystal (LC) phases. This ordering follows from the kinetic arrest of oligomer association into long-lived partially paired double helices, followed by reversible association of these pairs into linear aggregates that in turn condense into LC domains.

We demonstrate that topographic confinement in micro-channels can produce aligned domains of the columnar liquid crystal phase of complementary duplex short deoxyribonucleic acid (DNA) oligomers. Optical microscopy probing birefringence and fluorescence polarisation showed that the columnar liquid crystal phase of a 1:1 mixture of the complementary dodecamers 5′–CCTCAAAACTCC–3′ and 5′–GGAGTTTTGAGG–3′ in aqueous solution was aligned with the duplex DNA chains oriented normal to the channel axis. [ABSTRACT FROM AUTHOR]