DNA Nanotechnology: A foundation for Programmable Nanoscale Materials
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Introduction In 1982, N. Seeman published a landmark theoretical paper that spawned a new field—structural DNA nanotechnology.1 Motivated by the need to design artificial crystals rationally, Seeman proposed that DNA could be used as a programmable nanoscale building material. Rather than exist simply as isolated double helices, DNA strands could be designed to self-assemble into “branched junctions,” in which several DNA helices came together at a single point. These branched junctions brought DNA into the world of geometric design— they could be combined to fill space with a periodic threedimensional (3D) latticework, and that latticework could serve as a scaffold to arrange otherwise difficult-to-crystallize proteins so that the protein’s structures could be determined by x-ray crystallography. Seeman’s vision quickly widened to other applications, including a 3D “biochip,”2 which would use metal complexes as the bits of a molecular memory to store an unprecedented four petabytes per cubic centimeter. As of 2017, the synthesis of crystalline scaffolds for proteins, biochip memories, and other ambitious projects remain incomplete, yet the field of DNA nanotechnology has grown to be practiced by more than 100 labs worldwide and touches fields as different as plasmonics and biophysics. Key current questions include: What advantages does DNA offer over other materials? What challenges limit the widespread use of DNA nanotechnology? And, how might materials scientists
accelerate its impact on real-world applications in industry? To address these questions, we begin by comparing DNA to other materials. The most exciting new materials from the last quarter of a century, from high-temperature superconductors to quantum dots and graphene, have all had signature capabilities—for some physical property these supermaterials exhibit performance that exceeds all others. At first glance, DNA has no such signature capability. Optically, it is a simple UV absorber with technologically unimportant circular dichroism and weak fluorescence—DNA is no competition for tunable and bright quantum dots. Electronically, DNA shows nanometer-scale charge transport via tunneling,3 but this behavior pales in comparison to the micron-scale ballistic transport exhibited by carbon nanotubes and graphene. Catalytically, DNA can be coaxed into cutting other nucleic acids, and its enzymatically gifted cousin RNA likely played a central part in the origin of life, but neither is endowed with the catalytic prowess of protein. Instead, DNA’s role as stable genetic material, as well as recent interest in its use for mass data storage,4 might suggest that DNA’s signature capability is its ability to encode information. However, closer inspection reveals that it is in fact the information processing capabilities of DNA that render it immensely powerful: Solely DNA, RNA, and related unnatural polymers possess the exquisite specificity of Watson–Crick complementarity in which A pairs exclusively with T, and C
Mark Bathe, Massachusetts Institute of Technolo
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