DNA nanotechnology | applications

Applications

DNA nanotechnology provides one of the few ways to form designed, complex structures with precise control over nanoscale features. The field is beginning to see application to solve basic science problems in structural biology and biophysics. The earliest such application envisaged for the field, and one still in development, is in crystallography, where molecules that are difficult to crystallize in isolation could be arranged within a three-dimensional nucleic acid lattice, allowing determination of their structure. Another application is the use of DNA origami rods to replace liquid crystals in residual dipolar coupling experiments in protein NMR spectroscopy; using DNA origami is advantageous because, unlike liquid crystals, they are tolerant of the detergents needed to suspend membrane proteins in solution. DNA walkers have been used as nanoscale assembly lines to move nanoparticles and direct chemical synthesis. Further, DNA origami structures have aided in the biophysical studies of enzyme function and protein folding.[10][59]

DNA nanotechnology is moving toward potential real-world applications. The ability of nucleic acid arrays to arrange other molecules indicates its potential applications in molecular scale electronics. The assembly of a nucleic acid structure could be used to template the assembly of a molecular electronic elements such as molecular wires, providing a method for nanometer-scale control of the placement and overall architecture of the device analogous to a molecular breadboard.[10][26] DNA nanotechnology has been compared to the concept of programmable matter because of the coupling of computation to its material properties.[60]

In a study conducted by a group of scientists from iNANO and CDNA centers in Aarhus University, researchers were able to construct a small multi-switchable 3D DNA Box Origami. The proposed nanoparticle was characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and Förster resonance energy transfer (FRET). The constructed box was shown to have a unique reclosing mechanism, which enabled it to repeatedly open and close in response to a unique set of DNA or RNA keys. The authors proposed that this "DNA device can potentially be used for a broad range of applications such as controlling the function of single molecules, controlled drug delivery, and molecular computing."[61]

There are potential applications for DNA nanotechnology in nanomedicine, making use of its ability to perform computation in a biocompatible format to make "smart drugs" for targeted drug delivery. One such system being investigated uses a hollow DNA box containing proteins that induce apoptosis, or cell death, that will only open when in proximity to a cancer cell.[59][62] There has additionally been interest in expressing these artificial structures in engineered living bacterial cells, most likely using the transcribed RNA for the assembly, although it is unknown whether these complex structures are able to efficiently fold or assemble in the cell's cytoplasm. If successful, this could enable directed evolution of nucleic acid nanostructures.[26] Scientists at Oxford University reported the self-assembly of four short strands of synthetic DNA into a cage which can enter cells and survive for at least 48 hours. The fluorescently labeled DNA tetrahedra were found to remain intact in the laboratory cultured human kidney cells despite the attack by cellular enzymes after two days. This experiment showed the potential of drug delivery inside the living cells using the DNA ‘cage’.[63][64] A DNA tetrahedron was used to deliver RNA Interference (RNAi) in a mouse model, reported a team of researchers in MIT. Delivery of the interfering RNA for treatment has showed some success using polymer or lipid, but there are limits of safety and imprecise targeting, in addition to short shelf life in the blood stream. The DNA nanostructure created by the team consists of six strands of DNA to form a tetrahedron, with one strand of RNA affixed to each of the six edges. The tetrahedron is further equipped with targeting protein, three folate molecules, which lead the DNA nanoparticles to the abundant folate receptors found on some tumors. The result showed that the gene expression targeted by the RNAi, luciferase, dropped by more than half. This study shows promise in using DNA nanotechnology as an effective tool to deliver treatment using the emerging RNA Interference technology.[65][66] The DNA tetrahedron was also used in an effort to overcome the phenomena multidrug resistance. Doxorubicin (DOX) was conjugated with the tetrahedron and was loaded into MCF-7 breast cancer cells that contained the P-glycoprotein drug efflux pump. The results of the experiment showed the DOX was not being pumped out and apoptosis of the cancer cells was achieved.The tetrahedron without DOX was loaded into cells to test its biocompatibility, and the structure showed no cytotoxicity itself.[67]

Applications for DNA nanotechnology in nanomedicine also focus on mimicking the structure and function of naturally occurring membrane proteins with designed DNA nanostructures. In 2012, Langecker et al.[68] introduced a pore-shaped DNA origami structure that can self-insert into lipid membranes via hydrophobic cholesterol modifications and induce ionic currents across the membrane. This first demonstration of a synthetic DNA ion channel was followed by a variety of pore-inducing designs ranging from a single DNA duplex,[69] to small tile-based structures,[70][71][72][73][74] and large DNA origami transmembrane porins.[75] Similar to naturally occurring protein ion channels, this ensemble of synthetic DNA-made counterparts thereby spans multiple orders of magnitude in conductance. The study of the membrane-inserting single DNA duplex showed that current must also flow on the DNA-lipid interface as no central channel lumen is present in the design that lets ions pass across the lipid bilayer. This indicated that the DNA-induced lipid pore has a toroidal shape, rather than cylindrical, as lipid headgroups reorient to face towards the membrane-inserted part of the DNA.[69] Researchers from the University of Cambridge and the University of Illinois at Urbana-Champaign then demonstrated that such a DNA-induced toroidal pore can facilitate rapid lipid flip-flop between the lipid bilayer leaflets. Utilizing this effect, they designed a synthetic DNA-built enzyme that flips lipids in biological membranes orders of magnitudes faster than naturally occurring proteins called scramblases.[76] This development highlights the potential of synthetic DNA nanostructures for personalized drugs and therapeutics.

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