Multicolor Conjugated Polymer Thin Films with Tunable Responsivity to Oxidative and Reductive Environments.

Dynamic colors that respond to environmental changes are of great interest for diverse areas of science and technology ranging from chemical and biological sensors to smart information display. Here, we demonstrate a multitude of responsive colors from a conjugated polymer film arising from a thin-film interference. This mechanism provides an excellent control over the thin-film color by varying the film thickness, type of substrate, and degree of polaron population and is generally applicable to various conjugated polymers for further color variation. Furthermore, multiple sets of responsive colors are achieved from a single polymer layer by patterning the underlying substrate to spatially modify the interference conditions. Using this system, we demonstrate the reversible color changes induced by an oxidative or reductive environment with color responsivity controllable with the nature of the polaron state.

Charge-Transfer-Induced Self-Assembly of Doped Conjugated Block Copolymer Nanofibers.

Here, we report charge-transfer-driven self-assembly of conjugated block copolymers (BCP) into highly doped conjugated polymer nanofibers. The ground-state integer charge transfer (ICT) between a BCP composed of poly(3-hexylthiophene) and poly(ethylene oxide) (P3HT-b-PEO) and electron-deficient 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) induced spontaneous self-assembly of the donor and the acceptor into well-defined one-dimensional nanofibers. The presence of the PEO block plays an important role for the self-assembly by providing a polar environment that can stabilize nanoscale charge transfer (CT) assemblies. The doped nanofibers were responsive to various external stimuli such as heat, chemical, and light and exhibited efficient photothermal properties in the near-IR region. The CT-driven BCP self-assembly reported here provides a new platform for the fabrication of highly doped semiconductor nanostructures.

Janus Nanosheets with Face-Selective Molecular Recognition Properties from DNA-Peptide Conjugates.

Chemical and functional anisotropy in Janus materials offer intriguing possibilities for constructing complex nanostructures and regulating chemical and biological reactions. Here, the authors report the fabrication of Janus nanosheets from molecular building blocks composed of two information-carrying biopolymers, DNA and peptides. Experimental and structural modeling studies reveal that DNA-peptide diblock conjugates assemble into Janus nanosheets with distinct DNA and peptide faces. The surprising level of structural control is attributed to the exclusive parallel ß-sheet formation of phenylalanine-rich peptides. This approach is extended to triblock DNA1-peptide-DNA2 conjugates, which assemble into nanosheets presenting two different DNA on opposite faces. The Janus nanosheets with independently addressable faces are utilized to organize an enzyme pair for concerted enzymatic reactions, where enhanced catalytic activities are observed. These results demonstrate that the predictable and designable peptide interaction is a promising tool for creating Janus nanostructures with regio-selective and sequence-specific molecular recognition properties.

DNA-π Amphiphiles: A Unique Building Block for the Crafting of DNA-Decorated Unilamellar Nanostructures.

The unparalleled ability of DNA to recognize its complementary strand through Watson and Crick base pairing is one of the most reliable molecular recognition events found in natural systems. This highly specific sequence information encoded in DNA enables it to be a versatile building block for bottom-up self-assembly. Hence, the decoration of functional nanostructures with information-rich DNA is extremely important as this allows the integration of other functional molecules onto the surface of the nanostructures through DNA hybridization in a highly predictable manner. DNA amphiphiles are a class of molecular hybrids where a short hydrophilic DNA is conjugated to a hydrophobic moiety. Since DNA amphiphiles comprise DNA as the hydrophilic segment, their self-assembly in aqueous medium always results in the formation of nanostructures with shell made of DNA. This clearly suggests that self-assembly of DNA amphiphiles is a straightforward strategy for the ultradense decoration of a nanostructure with DNA. However, initial attempts toward the design of DNA amphiphiles were primarily focused on long flexible hydrocarbon chains as the hydrophobic moiety, and it has been demonstrated in several examples that they typically self-assemble into DNA-decorated micelles (spherical or cylindrical). Hence, molecular level control over the self-assembly of DNA amphiphiles and achieving diverse morphologies was extremely challenging and unrealized until recently.In this Account, we summarize our recent efforts in the area of self-assembly of DNA amphiphiles and narrate the remarkable effect of the incorporation of a large π-surface as the hydrophobic domain in the self-assembly of DNA amphiphiles. Self-assembly of DNA amphiphiles with flexible hydrocarbon chains as the hydrophobic moiety is primarily driven by the hydrophobic effect. The morphology of such nanostructures is typically predicted based on the volume ratio of hydrophobic to hydrophilic segments. However, control over the self-assembly and prediction of the morphology become increasingly challenging when the hydrophobic moieties can interact with each other through other noncovalent interactions. In this Account, the unique self-assembly behaviors of DNA-π amphiphiles, where a large π-surface acts as the hydrophobe, are described. Due to the extremely strong π-π stacking in aqueous medium, the assembly of the amphiphile is found to preferably proceed in a lamellar fashion (bilayer) and hence the morphology of the nanostructures can easily be tuned by the structural modification of the π-surface. Design principles for crafting various DNA-decorated lamellar nanostructures including unilamellar vesicles, two-dimensional (2D) nanosheets, and helically twisted nanoribbons by selecting suitable π-surfaces are discussed. Unilamellar vesicular nanostructures were achieved by using linear oligo(phenylene ethynylene) (OPE) as the hydrophobic segment, where lamellar assembly undergoes folding to form unilamellar vesicles. The replacement of OPE with a strongly π-stacking hydrophobe such as hexabenzocoronene (HBC) or tetraphenylethylene (TPE) provides extremely strong π-stacking compared to OPE, which efficiently directed the 2D growth for the lamellar assembly and led to the formation of 2D nanosheets. A helical twist in the lamella was achieved by the replacement of HBC with hexaphenylbenzene (HPB), which is the twisted analogue of HBC, directing the assembly into helically twisted nanoribbons. The most beneficial structural feature of this kind of nanostructure is the extremely dense decoration of their surface with ssDNA, which can further be used for DNA-directed organization of other functional nanomaterials. By exploring this, their potential as a nanoscaffold for predefined assembly of plasmonic nanomaterials into various plasmonic 1D, 2D, and 3D nanostructures through DNA hybridization is discussed. Moreover, the design of pH-responsive DNA-based vesicles and their application as a nanocarrier for payload delivery is also demonstrated.

Peptide-Driven Shape Control of Low-Dimensional DNA Nanostructures.

We report the rational design and fabrication of unusual low-dimensional DNA nanostructures through programmable and sequence-specific peptide interactions. Dual-bioactive block copolymers composed of DNA and amino acid-based polymers (DNA-b-poly(amino acid)) were synthesized by coupling oligonucleotides to phenylalanine (Phe)-based polymers. Unlike prototypical DNA block copolymers, which typically form simple spherical micelles, DNA-b-poly(amino acid) assemble into various low-dimensional structures such as nanofibers, ribbons, and sheets through controllable amino acid interactions. Moreover, DNA-b-poly(amino acid) assemblies can undergo protease-induced fiber-to-sheet shape transformations, where the morphology change is dictated by the type of enzymes and amino acid sequences. The peptide-based self-assembly reported here provides a programmable approach to fabricate dynamic DNA assemblies with diverse and unusual low-dimensional structures.

Dynamic Nanostructures from DNA-Coupled Molecules, Polymers, and Nanoparticles.

Dynamic and reconfigurable systems that can sense and react to physical and chemical signals are ubiquitous in nature and are of great interest in diverse areas of science and technology. DNA is a powerful tool for fabricating such smart materials and devices due to its programmable and responsive molecular recognition properties. For the past couple of decades, DNA-based self-assembly is actively explored to fabricate various DNA-organic and DNA-inorganic hybrid nanostructures with high-precision structural control. Building upon past development, researchers have recently begun to design and assemble dynamic nanostructures that can undergo an on-demand transformation in the structure, properties, and motion in response to various external stimuli. In this Review, recent advances in dynamic DNA nanostructures, focusing on hybrid structures fabricated from DNA-conjugated molecules, polymers, and nanoparticles, are introduced, and their potential applications and future perspectives are discussed.

DNA-Decorated, Helically Twisted Nanoribbons: A Scaffold for the Fabrication of One-Dimensional, Chiral, Plasmonic Nanostructures.

Crafting of chiral plasmonic nanostructures is extremely important and challenging. DNA-directed organization of nanoparticle on a chiral template is the most appealing strategy for this purpose. Herein, we report a supramolecular approach for the design of DNA-decorated, helically twisted nanoribbons through the amphiphilicity-driven self-assembly of a new class of amphiphiles derived from DNA and hexaphenylbenzene (HPB). The ribbons are self-assembled in a lamellar fashion through the hydrophobic interactions of HPB. The transfer of molecular chirality of ssDNA into the HPB core results in the bias of one of the chiral propeller conformations for HPB and induces a helical twist into the lamellar packing, and leads to the formation of DNA-wrapped nanoribbons with M-helicity. The potential of the ribbon to act as a reversible template for the 1D chiral organization of plasmonic nanomaterials through DNA hybridization is demonstrated.

DNA-Grafted Poly(acrylic acid) for One-Step DNA Functionalization of Iron Oxide Nanoparticles.

Here, we report one-step DNA functionalization of hydrophobic iron oxide nanoparticles (IONPs) using DNA-grafted poly(acrylic acid) (PAA- g-DNA). PAA- g-DNA was synthesized by coupling PAA to amine-modified oligonucleotides via solid-phase amide chemistry, which yielded PAA grafted with multiple DNA strands with high graft efficiencies. Synthesized PAA- g-DNA was utilized as a phase-transfer and DNA functionalization agent for hydrophobic IONPs, taking advantage of unreacted carboxylic acid groups. The resulting DNA-modified IONPs were well dispersed in aqueous solutions and possessed DNA binding properties characteristic of polyvalent DNA nanostructures, showing that this approach provides a simple one-step method for DNA functionalization of hydrophobic IONPs.

Self-assembly of DNA-tetraphenylethylene amphiphiles into DNA-grafted nanosheets as a support for the immobilization of gold nanoparticles: a recyclable catalyst with enhanced activity.

Preventing the aggregation of NPs and their recovery are the two major hurdles in NP based catalysis. Immobilization of NPs on a support has proven to be a promising strategy to overcome these difficulties. Herein we report the design of high aspect ratio two-dimensional (2D) crystalline DNA nanosheets formed from the amphiphilicity-driven self-assembly of DNA-tetraphenylethylene amphiphiles and also demonstrate the potential of DNA nanosheets for the immobilization of catalytically active NPs. The most remarkable feature of this approach is the high loading of NPs in a non-aggregated manner, and hence exhibiting enhanced catalytic activity. Recycling of NP loaded nanosheets for several cycles without reduction in catalytic efficiency by simple ultrafiltration is also demonstrated.

DNA-Decorated Two-Dimensional Crystalline Nanosheets.

Design and synthesis of high aspect ratio 2D nanosheets with surface having ultradense array of information-rich molecule such as DNA is extremely challenging. Herein, we report a universal strategy based on amphiphilicity-driven self-assembly for the crafting of high aspect ratio, 2D sheets that are densely surface-decorated with DNA. Microscopy and X-ray analyses have shown that the sheets are crystalline. The most unique feature of the sheets is DNA-directed surface addressability, which is demonstrated through the decoration of either faces of the sheet with gold nanoparticles through sequence-specific DNA hybridization. Our results suggest that this design strategy can be applied as a general approach for the synthesis of DNA decorated high aspect ratio sheets, which may find potential applications in materials science, drug delivery, and nanoelectronics.

Size controllable DNA nanogels from the self-assembly of DNA nanostructures through multivalent host-guest interactions.

Nanogels made of biomolecules are one of the potential candidates as a nanocarrier for drug delivery applications. The unique structural characteristics and excellent biocompatibility of DNA suggest that DNA nanogels would be an ideal candidate. Herein, a general design strategy for the crafting of DNA nanogels with controllable size using the multivalent host-guest interaction between ß-CD functionalized branched DNA nanostructures as the host and a star-shaped adamantyl-terminated 8-arm poly(ethylene glycol) polymer as the guest is reported. Our results reveal that multivalent host-guest interactions are necessary for the nanogel formation. Nanogels exhibit excellent biocompatibility, good cell permeability and high drug encapsulation ability, which are promising features for their application as a drug carrier. The encapsulation of doxorubicin, an anticancer drug, inside the hydrophobic network of the nanogel and its delivery into cancer cells are also reported. We hope that the general design strategy demonstrated for the creation of DNA nanogels may encourage other researchers to use this approach for the design of DNA nanogels of other DNA nanostructures, and explore the potential of DNA nanogels in drug delivery applications.

A pH-Responsive DNAsome from the Self-Assembly of DNA-Phenyleneethynylene Hybrid Amphiphile.

A pH-responsive DNAsome derived from the amphiphilicity-driven self-assembly of DNA amphiphile containing C-rich DNA sequence is reported. The acidification of DNAsome induces a structural change of C-rich DNA from random coil to an i-motif structure that triggers the disassembly of DNAsome and its subsequent morphological transformation into an open entangled network. The encapsulation of a hydrophobic guest into the membrane of DNAsome and its pH-triggered release upon acidification of DNAsome is also demonstrated.

Modular synthesis of supramolecular DNA amphiphiles through host-guest interactions and their self-assembly into DNA-decorated nanovesicles.

DNA nanostructures have found potential applications in various fields including nanotechnology, materials science and nanomedicine, hence the design and synthesis of DNA nanostructures is extremely important. Self-assembly of DNA amphiphiles provides an efficient strategy for the crafting of soft DNA nanostructures. However, the synthesis of DNA amphiphiles is always challenging. Herein, we show a non-covalent approach based on the host-guest interaction between ß-CD and adamantane for the synthesis of DNA amphiphiles, and report their amphiphilicity-driven self-assembly into DNA decorated vesicles. The DNA-directed surface addressability of the vesicles is demonstrated through their surface decoration with Au-NPs through DNA hybridization. Our results suggest that the non-covalent approach represents a simple, efficient and universal method for the synthesis of DNA amphiphiles, and provides an excellent strategy for the creation of smart DNA nanostructures.

Synthesis and self-assembly of DNA-chromophore hybrid amphiphiles.

DNA based spherical nanostructures are one of the promising nanostructures for several biomedical and biotechnological applications due to their excellent biocompatibility and DNA-directed surface addressability. Herein, we report the synthesis and amphiphilicity-driven self-assembly of two classes of DNA (hydrophilic)-chromophore (hydrophobic) hybrid amphiphiles into spherical nanostructures. A solid-phase "click" chemistry based modular approach is demonstrated for the synthesis of DNA-chromophore amphiphiles. Various spectroscopic and microscopic analyses reveal the self-assembly of the amphiphiles into vesicular and micellar assemblies with the corona made of hydrophilic DNA and the hydrophobic chromophoric unit as the core of the spherical nanostructures.

Self-assembly of DNA-oligo(p-phenylene-ethynylene) hybrid amphiphiles into surface-engineered vesicles with enhanced emission.

Surface-addressable nanostructures of linearly π-conjugated molecules play a crucial role in the emerging field of nanoelectronics. Herein, by using DNA as the hydrophilic segment, we demonstrate a solid-phase "click" chemistry approach for the synthesis of a series of DNA-chromophore hybrid amphiphiles and report their reversible self-assembly into surface-engineered vesicles with enhanced emission. DNA-directed surface addressability of the vesicles was demonstrated through the integration of gold nanoparticles onto the surface of the vesicles by sequence-specific DNA hybridization. This system could be converted to a supramolecular light-harvesting antenna by integrating suitable FRET acceptors onto the surface of the nanostructures. The general nature of the synthesis, surface addressability, and biocompatibility of the resulting nanostructures offer great promises for nanoelectronics, energy, and biomedical applications.