Nanotubes à la Carte: Wetting of Porous Templates

Nanotubes have an outstanding potential both for applications in nanotechnology and as the subject of basic research. Wetting of porous templates is a simple technique that overcomes many limitations of established preparation methods. It extends the range of processable materials, for example, by a broad range of multicomponent mixtures or by high‐performance polymers such as poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) and polytetrafluoroethylene (PTFE). Inducing controlled phase transitions generates a large specific surface, a specific nanoporosity, or oriented crystalline domains within the nanotube walls. Template wetting provides customized nanotubes and allows us to investigate how the wall curvature affects the structure formation.     

Biomimetic DNA Nanotubes: Nanoscale Channel Design and Applications

Biomacromolecular nanotubes play important physiological roles in transmembrane ion/molecule channeling, intracellular transport, and inter‐cellular communications. While genetically encoded protein nanotubes are prevalent in vivo, the in vitro construction of biomimetic DNA nanotubes has attracted intense interest with the rise of structural DNA nanotechnology. The abiotic use of DNA assembly provides a powerful bottom‐up approach for the rational construction of complex materials with arbitrary size and shape at the nanoscale. More specifically, a typical DNA nanotube can be assembled either with parallel‐aligned DNA duplexes or by closing DNA tile lattices. These artificial DNA nanotubes can be tailored and site‐specifically modified to realize biomimetic functions including ionic or molecular channeling, bioreactors, drug delivery, and biomolecular sensing. In this Minireview, we aim to summarize recent advances in design strategies, including the characterization and applications of biomimetic DNA nanotubes.     

Hollow Self‐Doped Polyaniline Micro/Nanostructures: Microspheres,Aligned Pearls,and Nanotubes

Hollow self‐doped polyaniline (SPAN) micro/nanostructures, such as hollow microspheres, aligned pearls, and nanotubes, have been synthesized by a one‐step chemical oxidation copolymerization of aniline (AN) and m‐aminobenzenesulfonic acid (SAN) using ammonium peroxydisulfate (APS) as the oxidant in aqueous solution. The process is facile and free of any template, surfactant, and external dopants. The shapes and sizes of the hollow SPAN micro/nanostructures can be controlled by adjusting the synthetic parameters, such as the molar ratios of AN and SAN, the concentrations of monomers, and the molar ratios of the monomer and APS. The formation of hollow SPAN micro/nanostructures is possibly related to the self‐assembly of SPAN oligomers at the early stage of the copolymerization reaction. The molecular structures of the SPAN micro/nanostructures were determined by FT‐IR spectroscopy, which reveales that SO groups are bonded to the aromatic rings in SPAN chains.

     

Decorating Polypyrrole Nanotubes with Au Nanoparticles by an In Situ Reduction Process

Au nanoparticle‐decorated polypyrrole nanotubes (defined as PPy/Au nanocomposites) are prepared by an in situ reduction process. Polypyrrole (PPy) nanotubes are prepared by a self‐degraded template method, and Au nanoparticles are deposited in situ by the reduction of HAuCl₄. The size and uniformity of the Au nanoparticles that decorate the PPy nanotubes can be controlled by adjusting the experimental conditions, such as the stabilizers used and the reaction temperature. The morphologies and optical properties of the nanocomposites have been characterized by scanning electron microscopy, transmission electron microscopy, UV‐vis, and FT‐IR spectroscopy. Conductivity measurements show that the conductivities of the nanocomposites decrease with a decrease of temperature, and the conductivity–temperature relationship obeys the quasi‐one dimensional variable range hopping model.

     

In Vivo Remote Control of Reactions in Caenorhabditis elegans by Using Supramolecular Nanohybrids of Carbon Nanotubes and Liposomes

A supramolecular nanohybrid based on carbon nanotubes and liposomes that is highly biocompatible and capable of permeation through cells is described. The nanohybrid can be loaded with a variety of functional molecules and is structurally controlled by near‐infrared laser irradiation for the release of molecules from the nanohybrids in a targeted manner via microscopy. We implemented the controlled release of molecules from the nanohybrids and demonstrated remote regulation of the photoinduced nanohybrid functions. As a proof of principle, nanohybrids loaded with amiloride were successfully used in the spatiotemporally targeted blocking of amiloride‐sensitive mechanosensory neurons in living Caenorhabditis elegans. Our prototype could inspire new designs for biomimetic parasitism and symbiosis, and biologically active nanorobots for the higher‐level manipulation of organisms.     

Polyampholyte‐Wrapped Carbon Nanotubes: Preparation and Internalization by Embryonic Fibroblast Cells

The cytotoxicity and cellular uptake of carbon nanotubes (CNTs) has recently attracted considerable interest because of the issue of biosphere‐nanomaterial interactions. The biocompatibility of CNTs is determined by the metal impurities in the CNTs, the size of the CNTs and the CNT dispersion states; in particular, the type of surface modifications on the CNTs affects how they interact with cells and determines their cytotoxicity and cellular uptake. In this study, biocompatible single‐walled carbon nanotubes (SWNTs) wrapped with a water‐soluble copolymer, poly[2‐(dimethylamino)ethyl methacrylate‐co‐methacrylic acid] (PDM), were prepared. We report that these SWNTs have enhanced water dispersibility and cellular internalization but no significant cytotoxic activity against mouse embryonic fibroblast NIH‐3T3 cells.

     

Diameter Selection of Carbon Nanotubes in Polymer/SWCNT Nanowire Arrays Fabricated by Template Wetting

Arrays of polymer/SWCNT (single‐wall carbon nanotube) nanowires supported on a residual nanocomposite film are prepared by melt wetting using porous anodic aluminum oxide (AAO) as a template. The aggregation parameter of SWCNTs extracted from the analysis of their Raman radial breathing modes gives the highest value for native SWCNTs, indicating that they tend to organize into bundles giving rise to a high degree of aggregation. However, the lowest value achieved at the interface between the nanocomposite film and the nanoarray is explained considering that the forces acting during infiltration are able to disrupt the SWCNT bundles inducing nanotube dispersion. In addition, scanning the nanoarrays along the nanowires length by Raman microscopy has shown a diameter selection of SWCNTs by the AAO membrane. The results reported in this work reveal that it is possible to fabricate arrays of nanowires with homogeneous SWCNT distribution along tens of microns, optimizing nanotube dispersion.     

Nanotubes fabricated from Ni-naphthalocyanine by a template method

Novel naphthalocyanine (Nc) nanotubes with special wall structures were fabricated by a template method using Nc molecules as building blocks. Thermal stabilization of the ordered columnar structures of the tetrakis(tert-butyl)naphthalocyanine (Ni-BNc) molecules, induced from the pi-pi interactions in the nanoscale channels of an alumina template, resulted in Nc nanotubes with walls consisting of well-ordered Nc molecular disks. Further thermal treatment of Ni-BNc at 600 degrees C produced carbonized Nc nanotubes containing ordered columnar, graphitic wall structures with the graphene disks arranged perpendicular to the tube axis. These nanotubes may be useful for extending the application of Nc molecules for nanodevice fabrication.     

Light‐Harvesting Nanotubes Formed by Supramolecular Assembly of Aromatic Oligophosphates

A 2,7‐disubstituted phosphodiester‐linked phenanthrene trimer forms tubular structures in aqueous media. Chromophores are arranged in H‐aggregates. Incorporation of small quantities of pyrene results in the development of light‐harvesting nanotubes in which phenanthrenes act as antenna chromophores and pyrenes as energy acceptors. Energy collection is most efficient after excitation at the phenanthrene H‐band. Fluorescence quantum yields up to 23 % are reached in pyrene doped, supramolecular nanotubes.     

Biofunctionalization of Multiwalled Carbon Nanotubes by Irradiation of Electropolymerized Poly(pyrrole–diazirine) Films

A photoactivatable poly(pyrrole–diazirine) film was synthesized and electropolymerized as a versatile tool for covalent binding of laccase and glucose oxidase on multiwalled carbon nanotube coatings and Pt, respectively. Irradiation of the functionalized nanotubes allowed photochemical grafting of laccase and its subsequent direct electrical wiring, as illustrated by the electrocatalytic reduction of oxygen. Moreover, covalent binding of glucose oxidase as model enzyme, achieved by UV activation of electropolymerized pyrrole–diazirine, allowed a glucose biosensor to be realized. This original method to graft biomolecules combines electrochemical and photochemical techniques. The simplicity of this new method allows it to be extended easily to other biological systems.     

Extraction of (9,8) Single‐Walled Carbon Nanotubes by Fluorene‐Based Polymers

Selective polymer wrapping is a promising approach to obtain high‐chiral‐purity single‐walled carbon nanotubes (SWCNTs) needed in technical applications and scientific studies. We showed that among three fluorene‐based polymers with different side‐chain lengths and backbones, poly[(9,9‐dihexylfluorenyl‐2,7‐diyl)‐co‐(9,10‐anthracene)] (PFH‐A) can selectively extract SWCNTs synthesized from the CoSO₄/SiO₂ catalyst, which results in enrichment of 78.3 % (9,8) and 12.2 % (9,7) nanotubes among all semiconducting species. These high‐chiral‐purity SWCNTs may find potential applications in electronics, optoelectronics, and photovoltaics. Furthermore, molecular dynamics simulations suggest that the extraction selectivity of PFH‐A relates to the bending and alignment of its alkyl chains and the twisting of its two aromatic backbone units (biphenyl and anthracene) relative to SWCNTs. The strong π–π interaction between polymers and SWCNTs would increase the extraction yield, but it is not beneficial for chiral selectivity. Our findings suggest that the matching between the curvature of SWCNTs and the flexibility of the polymer side chains and the aromatic backbone units is essential in designing novel polymers for selective extraction of (n,m) species.     

Nanospheres,Nanotubes, Toroids,and Gels with Controlled Macroscopic Chirality

The interaction of a highly dynamic poly(aryl acetylene) (poly‐ 1 ) with Li⁺, Na⁺_, and Ag⁺ leads to macroscopically chiral supramolecular nanospheres, nanotubes, toroids, and gels. With Ag⁺, nanospheres with M helicity and tunable sizes are generated, which complement those obtained from the same polymer with divalent cations. With Li⁺ or Na⁺, poly‐ 1 yields chiral nanotubes, gels, or toroids with encapsulating properties and M helicity. Right‐handed supramolecular structures can be obtained by using the enantiomeric polymer. The interaction of poly‐ 1 with Na⁺ produces nanostructures whose helicity is highly dependent on the solvation state of the cation. Therefore, structures with either of the two helicities can be prepared from the same polymer by manipulation of the cosolvent. Such chiral nanotubes, toroids, and gels have previously not been obtained from helical polymer–metal complexes. Chiral nanospheres made of poly(aryl acetylene) that were previously assembled with metal(II) species can now be obtained with metal(I) species.     

Nanoparticle‐Assisted Alignment of Carbon Nanotubes on DNA Origami

Aligning carbon nanotubes (CNTs) is a key challenge for fabricating CNT‐based electronic devices. Herein, we report a spherical nucleic acid (SNA) mediated approach for the highly precise alignment of CNTs at prescribed sites on DNA origami. We find that the cooperative DNA hybridization occurring at the interface of SNA and DNA‐coated CNTs leads to an approximately five‐fold improvement of the positioning efficiency. By combining this with the intrinsic positioning addressability of DNA origami, CNTs can be aligned in parallel with an extremely small angular variation of within 10°. Moreover, we demonstrate that the parallel alignment of CNTs prevents incorrect logic functionality originating from stray conducting paths formed by misaligned CNTs. This SNA‐mediated method thus holds great potential for fabricating scalable CNT arrays for nanoelectronics.