Origami is nothing new to us. Origami refers to the art of folding and sculpting a flat sheet of paper to create different funny shapes. The word 'origami' is a blend of two Japanese words our (to fold) and kami (paper). So, origami is the art of paper folding which is basically an ancient Japanese culture. However, in modem usage, the word ‘origami’ is used as an inclusive term for all folding practices, regardless of their culture of origin. Origami folders often use the Japanese word ‘kirigami’ (kirimas – to cut) to refer to designs which use cuts, although cutting is more characteristic of Chinese paper crafts. The most classical origami model is probably the Japanese paper crane and it is believed that its wings carry souls up to paradise in Japanese culture. It is often used as a ceremonial wrapper or restaurant table decoration. Akira Yoshizawa, Japanese master paper folder is widely acclaimed as the father of modern origami.

Interestingly, the art of paper folding is no more confined in making funny paper shapes; rather the concept is now being used in making various useful patterns and structures with DNA strands called DNA origami. The number of folds is usually less compared to paper-origami, but they can be combined in a variety of ways to make intricate designs.

The idea of using DNA as a construction material was first introduced in the early 1980s by Nadrian Seeman, professor of DNA Nanotechnology at New York University (NYU) and the field began to attract widespread interest in the mid-2000s. Inspired by the M.C. Escher’s woodcut Depth which is pretty similar in shape to a six-arms DNA junctions, Ned realized that a 3D lattice could be constructed from DNA. In pursuit of this goal, Seeman's laboratory published the synthesis of the first three-dimensional nanoscale object, a cube made of DNA, in 1991. The first DNA nanomachine—a device that changes its structure in response to an input—was also demonstrated by him in 1999. In 2006, Rothemund at California Institute of Technology (Caltech) first demonstrated the DNA origami method for forming folded DNA structures of arbitrary shape.

It is very well known that DNA is a double helix, discovered by Watson & Crick in 1953. DNA is an easily programmable material that is useful for building molecular machines. The components of its opposite strands, which we call genetic alphabets (A, T, G, C) are complementary to each other enabling them to bind together to form a rigid double helical architecture pretty similar to a spiral staircase.

Nanotechnology is often defined as the study of materials and devices with features on a scale below 100 nanometers. Nano means 1 X 10-9 i.e. one billionth of anything. One nanometer (1 nm) equals one-billionth of a meter. The DNA molecule has appealing features for use in nanotechnology: its minuscule size, with a diameter of about 2 nm, its short structural repeat of about 3.5 nm, and its 'stiffness', with a persistence length around 50 nm. Due to its high degree of customization and spatial addressability, DNA origami provides a versatile platform to engineer nanoscale structures and devices that can sense, compute, and actuate. DNA nanotechnology is the design and manufacture of artificial DNA structures for technological uses. In this field, DNAs are used as non-biological engineering materials rather than as the carriers of genetic information in living cells. Because of its high level of programmability, reliable base-pairing specificity, high physicochemical stability, and readily automated synthesis, DNA is a suitable candidate for making customized structures. Researchers in the field have created stable structures such as 2D and 3D crystal lattices, nanotubes, branched junctions of arbitrary shapes, and functional devices such as molecular machines, DNA computers, nanorobots and much more!

DNA machine is a molecular machine constructed from DNA strands. Since DNA assembly of the double helix is based on strict rules of base pairing that allow portions of the strand to be connected based on their sequence. This "selective stickiness" is a key advantage in the construction of DNA machines. In 2000, Bernard Yurke and co-workers reported the construction of molecular tweezers out of DNA. The DNA tweezers contain three strands: A, B and C where Strand A is fastened to half of strand B and half of strand C. Strand A acts as a hinge so that the two "arms" — AB and AC — can move. The 2016 Nobel Prize in Chemistry was awarded to Jean-Pierre Sauvage, Sir J. Fraser Stoddart, and Bernard L. Feringa for the design and synthesis of molecular machines for chemical synthesis.

DNA walker is another kind of nanomachines capable of moving along a DNA "track". The concept of a DNA walker was first defined and named by John H. Reif in 2003. DNA walkers have potential applications ranging from nanomedicine to nanorobotics. In late 2015, Yehl et al. improved the DNA walker's function by increasing its velocity, with a low-cost, low-tech diagnostics machine capable of detecting heavy-metal contamination in water. In 2018 Nils Walter and his team designed a DNA walker that can move at a speed of 300 nm per minute.

Nanomedicine is a branch of medicine that applies the knowledge and tools of nanotechnology for the prevention and treatment of disease. It involves the use of nanoscale materials, such as biocompatible nanoparticles and nanorobots, for diagnosis, delivery or sensing purposes in living organisms. There are multitude of applications of DNA structures in nanomedicine, making use of its ability to make "smart drugs" for targeted drug delivery, as well as for diagnostic applications. One such a system uses a hollow DNA box containing proteins capable of inducing cell death, that will only open while it is in proximity to a cancer cell. Scientists at Oxford University reported the self-assembly of four short arms of synthetic DNA into a cage forming a tetrahedron which can enter cells and survive. Doxorubicin, a well-known anti-cancer drug was loaded into the tetrahedron and injected into MCF-7, a category of breast cancer cells. The results of the experiment showed that Doxorubicin was able to kill cancer cells efficiently.

DNA computer is an assembly of DNA strands that can process data in a similar way as an electronic computer, and has the potential to solve complex problems and store a greater amount of information, for substantially less energy costs than do electronic microprocessors. DNA-based computation dates from Leonard Adleman's landmark report in 1994, where he used DNA to solve the 'Hamiltonian path' problem, a variant of the 'travelling salesman' problem. The idea is to establish whether there is a path between two cities, given an incomplete set of available roads. Adleman used strands of DNA to represent cities and roads and encoded the sequences so that a strand representing a road would connect (according to the rules of base pairing) to any two strands representing a city. By mixing the strands, joining the cities connected by roads, and weeding out any 'wrong answers', he showed that the strands could self-assemble to solve the problem.

Over the last four decades, researchers in the field of DNA nanotechnology have successfully demonstrated that DNA is not merely a genetic material in cells, rather, it is a powerful building material for creating useful objects with nanometer precision. DNA origami techniques are capable of engineering custom structures with high addressability helping nanoscience research. It will be exciting if we see its more widespread real-life applications in human healthcare, materials fabrication, electronics and beyond.

References

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