Cheng Tian

DNA-directed three-dimensional protein organization.

All bound together: self-assembled symmetric DNA polyhedra were used to organize proteins in 3D space. Biotin moieties were incorporated into the self-assembled symmetric DNA polyhedra. Upon incubation with streptavidin (STV) protein, an STV protein became bound to each polyhedral face, thus resulting in well-structured DNA polyhedra/STV complexes. This strategy was also applied to different 3D DNA nanostructures and different proteins.

DNA nanocages swallow gold nanoparticles (AuNPs) to form AuNP@DNA cage core-shell structures.

DNA offers excellent programming properties to nanomaterials syntheses. Host-guest interaction between DNA nanostructures and inorganic nanoparticles (NPs) is of particular interest because the resulting complexes would possess both programming properties intrinsic to DNA and physical properties associated with inorganic NPs, such as plasmonic and magnetic features. Here, we report a class of core-shell complexes (AuNP@DNA cages): hard gold NPs (AuNPs) are encapsulated in geometrically well-defined soft DNA nanocages. The AuNP guest can be further controllably released from the host (DNA nanocages), pointing to potential applications in surface engineering of inorganic NPs and cargo delivery of DNA nanocages.

A smart DNA tetrahedron that isothermally assembles or dissociates in response to the solution pH value changes.

This communication reports a DNA tetrahedron whose self-assembly is triggered by an acidic environment. The key element is the formation/dissociation of a short, cytosine (C)-containing, DNA triplex. As the solution pH value oscillates between 5.0 and 8.0, the DNA triplex will form and dissociate that, in turn, leads to assembly or disassembly of the DNA tetrahedron, which has been demonstrated by native polyacrylamide gel electrophoresis (PAGE). We believe that such environment-responsive behavior will be important for potential applications of DNA nanocages such as on-demand drug release.

Directed Self‐Assembly of DNA Tiles into Complex Nanocages

Tile-based self-assembly is a powerful method in DNA nanotechnology and has produced a wide range of well-defined nanostructures. But the resulting structures are relatively simple. Increasing the structural complexity and the scope of the accessible structures is an outstanding challenge in molecular self-assembly. A strategy to partially address this problem by introducing flexibility into assembling DNA tiles and employing directing agents to control the self-assembly process is presented. To demonstrate this strategy, a range of DNA nanocages have been rationally designed and constructed. Many of them can not be assembled otherwise. All of the resulting structures have been thoroughly characterized by gel electrophoresis and cryogenic electron microscopy. This strategy greatly expands the scope of accessible DNA nanostructures and would facilitate technological applications such as nanoguest encapsulation, drug delivery, and nanoparticle organization.

Construction of RNA nanocages by re-engineering the packaging RNA of Phi29 bacteriophage

RNA nanotechnology promises rational design of RNA nanostructures with wide array of structural diversities and functionalities. Such nanostructures could be used in applications such as small interfering RNA delivery and organization of in vivo chemical reactions. Though having impressive development in recent years, RNA nanotechnology is still quite limited and its programmability and complexity could not rival the degree of its closely related cousin: DNA nanotechnology. Novel strategies are needed for programmed RNA self-assembly. Here, we have assembled RNA nanocages by re-engineering a natural, biological RNA motif: the packaging RNA of phi29 bacteriophage. The resulting RNA nanostructures have been thoroughly characterized by gel electrophoresis, cryogenic electron microscopy imaging and dynamic light scattering.

DNA Polyhedra with T-Linkage

This paper reports a strategy for DNA self-assembly. Cross-over-based DNA nanomotifs are held together by T-junctions instead of commonly used sticky-end cohesion. We have demonstrated this strategy by assembling a DNA tetrahedron, an octahedron, and an icosahedron. The resulting DNA polyhedra contain out-pointing, short DNA hairpin spikes. These hairpins are well-structured relative to the polyhedra core and provide potential locations for introduction of functional chemicals such as proteins and gold nanoparticles. The T-linked DNA polyhedra have been characterized by polyacrylamide gel electrophoresis, atomic force microscopy, and dynamic light scattering.

Reversibly Switching the Surface Porosity of a DNA Tetrahedron

The ability to reversibly switch the surface porosity of nanocages would allow controllable matter transport in and out of the nanocages. This would be a desirable property for many technological applications, such as drug delivery. To achieve such capability, however, is challenging. Herein we report a strategy for reversibly changing the surface porosity of a self-assembled DNA nanocage (a DNA tetrahedron) that is based on DNA hydridization and strand displacement. The involved DNA nanostructures were thoroughly characterized by multiple techniques, including polyacrylamide gel electrophoresis, dynamic light scattering, atomic force microscopy, and cryogenic electron microscopy. This work may lead to the design and construction of stimuli-responsive nanocages that might find applications as smart materials.

Synchronization of Two Assembly Processes To Build Responsive DNA Nanostructures

Herein, we report a strategy for the synchronization of two self-assembly processes to assemble stimulus-responsive DNA nanostructures under isothermal conditions. We hypothesized that two independent assembly processes, when brought into proximity in space, could be synchronized and would exhibit positive synergy. To demonstrate this strategy, we assembled a ladderlike DNA nanostructure and a ringlike DNA nanostructure through two hybridization chain reactions (HCRs) and an HCR in combination with T-junction cohesion, respectively. Such proximity-induced synchronization adds a new element to the tool box of DNA nanotechnology. We believe that it will be a useful approach for the assembly of complex and responsive nanostructures.

Structural Transformation: Assembly of an Otherwise Inaccessible DNA Nanocage†

A strategy of structural transformation for the assembly of DNA nanocages that can not be assembled directly is described. In this strategy, a precursor DNA nanocage is assembled first and then is isothermally transformed into a desired, complicated nanocage. A dramatic, conformational change accompanies the transformation. This strategy has been proven to be successful by native polyacrylamide gel electrophoresis (PAGE) and cryogenic electron microscopy (cryoEM) imaging. We expect that the strategy of structural transformation will be useful for the assembly of many otherwise inaccessible DNA nanostructures and help to increase the structural complexity of DNA nanocages.

Controlling the chirality of DNA nanocages.

We report a rational approach for controlling the chirality of self-assembled DNA nanocages at the nanoscale. Chirality on the nanoscale originates from the asymmetric characteristics of the component DNA building block (DNA nanomotif), but is distinct from the intrinsic, molecular-level chirality of the DNA duplex. By purposely removing two-dimensional (2D) rotation symmetry from the DNA nanomotif, we can control the three-dimensional (3D) chirality of the DNA nanocages. Such chiral control would be useful for tuning the photonic/ optical properties of nanophotonic devices when DNA nanostructures are used as structural scaffolds. [1–3] Chirality is an important structural feature across all size scales, from molecules to galaxies. Nanoscaled (1–100 nm) chirality bridges between the intrinsic chirality of molecules and the macroscale chirality of materials. Chemical synthesis and stereo-selective separation readily allow preparation of chiral molecules, and advanced fabrication methods can be used to fabricate chiral structures at the micrometer scale. However, there is a gap between these two approaches, how to rationally design and prepare chiral objects at the nanometer scale (1–100 nm). Such nanoscaled chiral structures have many technological applications, for example, chiral plasmonic devices. [4–6] Biomimetic, supramolecular DNA selfassembly is a powerful technique for building nanostructures because of its programmability and well-established secondary structure. [7–9] DNA nanocages [10–22] are intrinsically chiral at the molecular level, because DNA duplexes are chiral. In addition, the geometric folding, twisting, bending, and association of the component DNA duplexes in DNA nanostructures could also lead to nanoscaled chiral features. [14] Turberfield and co