Advanced Materials

This Special Section contains sixteen papers covering a range of exciting developments in bionanotechnology. We hope that readers from both the materials science and the biomedical research communities can find the work presented here beneficial to their current research and begin to venture into this interdisciplinary field.

Hybrid nanoparticles with multi-functional capabilities of targeted infection, magnetic resonance (MR) imaging, and gene delivery are developed by fusing virus and MnMEIO magnetic nanoparticles. Their successful utilizations for in vitro target-specific MR imaging and enhanced green fluorescent protein (eGFP) gene delivery into CAR-positive cells are demonstrated.

This Special Section contains sixteen papers covering a range of exciting developments in bionanotechnology. We hope that readers from both the materials science and the biomedical research communities can find the work presented here beneficial to their current research and begin to venture into this interdisciplinary field.

Cell sheet technology utilizing of temperature-responsive culture dishes has been applied to tissue engineering. Via this technology, cell sheets can be transplanted to host tissues without using biodegradable scaffolds. This Progress Report summarizes temperature-controlled cell adhesion-detachment behavior and applications of the cell sheet technology to regeneration of cornea, periodontal ligament, bladder epithelia, oesophageal epithelia, myocardium, and liver.

Au and Ag nanoparticles have optical properties that make them useful as tags in a wide variety of measurement schemes. This Progress Report discusses several different methods by which these nanoparticles can be used as surface-enhanced Raman scattering (SERS) tags for the measurement of biomolecules.

Hybrid nanoparticles with multi-functional capabilities of targeted infection, magnetic resonance (MR) imaging, and gene delivery are developed by fusing virus and MnMEIO magnetic nanoparticles. Their successful utilizations for in vitro target-specific MR imaging and enhanced green fluorescent protein (eGFP) gene delivery into CAR-positive cells are demonstrated.

Signal processing methods and constraints for discerning the fluorescence signals of the QD-barcodes are explored. QD-barcodes and their corresponding fluorescence spectra (see figure) require signal processing algorithms in order to be uniquely identified. Using these algorithms, we determined the number of available barcodes for use in biological detection. We also studied the impact of chemical constraints such as buffer and pH level on the barcode and read-out design.

Micro- to nanoscale elastomeric post arrays with different post geometries were used to probe the effects of local substrate architecture on cell spreading and traction force generation in adherent cells (see figure). As post density increases, cell morphology on the post arrays increasingly resembles that of cells on continuous substrates. In addition, contractile strain energy generated by cells remained constant across substrates with different post stiffness or adhesive surface area.

Human endothelial and lung epithelial cells were exposed to nanosized Pt shapes following acellular analyses of their oxidant potential. Despite clear evidence of particle uptake by cells, the Pt nanoparticles were not found to induce cytotoxicity or oxidative stress in either cell type. Results from in vivo respiratory tract exposures suggest that the particles are retained by lung tissue and that minimal-mild lung inflammation results from exposure to the nanosized Pt particles.

Calcium-doped organosilicate nanoparticles for gene delivery are prepared by using a surfactant-mediated sol-gel synthesis. The enhanced uptake of these nanoparticles by osteoblast cells (see figure) makes them promising candidates for the transfection of bone cells. The complexes of Ca-SiO₂ nanoparticles with DNA transfect bone cells effectively without inducing cytotoxicity in vitro.

Folate-conjugated gold nanorods targeted to tumor cell surfaces produced severe membrane damage upon near-infrared irradiation. Photoinduced injury to the plasma membrane resulted in a rapid increase in intracellular calcium (shown in green) with subsequent disruption of the actin network, featured prominently by the formation of membrane blebs.

Remote control over reactions in multicompartment capsules is investigated. Dual-compartment capsules were constructed by consecutive fabrication of the inner and the outer parts of CaCO₃ microcapsules separated by a polyelectrolyte multilayer IR-sensitized by nanoparticle doping. Upon near-infrared laser illumination the contents of the inner capsules are mixed with the outer one. This research paves the way to a simple method for performing sophisticated bioreactions in confined volumes.

Quantum dot bioconjugates can be used for multiplexed and quantitative detection of tumor biomarkers in cells and tissues. This new technology should have significant impact on molecular pathology if validated with traditional techniques (such as western blotting, FISH, and IHC), and with large-scale clinical studies. In addition, it could also become the first clinical application of quantum dots.

Enzymatic formation of supramolecular nanofibers is demonstrated as a novel approach to induce intracellular hydrogelation and control the fate of cells or cellular functions, which can lead to a new paradigm for developing biomaterials to manage cellular artificial nanostructures (CAN), understand cellular functions beyond the molecular level, and create novel therapeutics.

A new strategy to construct shell crosslinked nanoparticles has been developed, containing large numbers of effective DOTAlysines per particle (> 400) for ⁶⁴Cu radiolabeling. These ⁶⁴Cu-complexed nanoparticles show impressive specific activities (ca. 400 μCi μg^–1), which suggests that they will serve as highly sensitive in vivo PET tracers at low administering doses.

A dopamine-PEG based ligand is synthesized and used to stabilize monodisperse 9 nm Fe₃O₄ nanoparticles in physiological conditions and against non-specific uptake by macrophage cells. Such stable nanoparticles can be used to enhance the efficiency in target-specific drug delivery and to increase the signal-to-noise ratio in magnetic resonance imaging (MRI).

Studies of silver nanoparticle formation using MWNT-protein/polypeptide conjugates are reported. Our findings suggest that there is selectivity in the formation of silver nanoparticles depending on the nature of the protein. Protein-mediated mineralization is facile and can be carried out under mild conditions, thereby enabling retention of the biological activity of the protein.

The binding kinetics of fluorescently labeled microtubules to kinesin-coated surfaces permits the determination of the density of kinesin motor proteins adhered to the surface in the range of 0.1 – 30 μm^–2. This extreme sensitivity, corresponding to protein coverages of 0.004 – 1 ng cm^–2, enables the characterization of advanced non-fouling coatings, such as (EG)₃OH-terminated SAMs and PEGMA with applications in biomedical engineering and bionanotechnology.

Gold nanocages represent a novel class of biocompatible nanostructures, with potential cancer diagnostic and therapy properties intrinsic to their surface plasmon resonance (SPR). They are prepared by the galvanic replacement reaction between Ag nanocubes and HAuCl₄ solution, and their SPR peak position can be precisely tuned into the near-infrared. Recent advances in the use of Au nanocages as optical contrast enhancement and photothermal therapy agents are discussed.

Liquid-electrolyte and solid-state dye-sensitized solar cells (DSCs) are an important candidate for future energy solutions. Recent developments in DSC research are highlighted in this Progress Report . Underlying processes, such as charge generation, transport, recombination, and charge collection are discussed. Recently developed alternative device concepts are also described, including extremely thin absorber cells, inorganic p-type hole-transporter cells, and a range of non-TiO2 mesoporous metal-oxide electrodes employed in DSCs.

Bioelectronics is a technology platform that enables signal transduction between biology and traditional electronics. This technology becomes successful only if electronic signals can be translated into biological equivalences, and vice versa, at proper temporal and spatial resolution. In addition, bioelectronic devices must exhibit proper biocompatibility and biostability to function properly over time. Organic electronic devices enable several advantages as compared to inorganic electronics, in many respects, and recent progress in organic bioelectronics is described in this Review.

Achieving high sensitivity and low detection limits are major challenges in biosensing. In this Review, recent advances in carbon nanotube-assisted biodetection through field effect transistor and electrochemical architectures (see figure) are summarized, along with various methodologies for signal amplification.

Spatially forced self-organized microwrinkles using a substrate with periodic nanopatterns are fabricated by nanolithography. The hard (metal, organic or inorganic/organic) film formed on the patterned substrate forms precisely directed wrinkles under lateral compression. The wavelength is resonantly forced to the integral multiples of the periodicity of nanopatterns.

Complex solid-state hydrides can store hydrogen at very high volumetric and gravimetric densities. We present a theoretical framework, which automatically determines phase diagrams and thermodynamically favored hydrogen storage reactions in complex multicomponent systems, such as Li-Mg-N-H (see figure). This method can be used to efficiently scan the phase space and pinpoint those compositions, which have the greatest potential for thermodynamically reversible H₂ storage.

Quarterthiophenes with long pendant alkyl side-chains exhibit a unique, hitherto unreported polymorphism arising from side-chain comformational changes. Those with long backbone structures show two different side-chain conformationally induced polymorphs, one with a fully extended side-chain and one with a bent side-chain conformations. This unique polymorphism is a result of subtle differences in molecular architecture and can be induced by crystallization conditions.

The photoinduced isotropic (PHI) state of cholesteric liquid crystals (CLCs) induced by the UV irradiation of a highly doped (azobenzene liquid crystal) CLC can be stable for tens of hours dominated by the lifetime of the cis isomers. Low-power laser light can be used to write complex 2D images (a car is shown), where the contrast arises from restoration of the reflective cholesteric phase.

Highly-conductive organic charge-transfer complex films are successfully fabricated by an inkjet printing technique in which the soluble donor and acceptor components are printed individually and combine on the substrate to form complex films. The method enables us to produce conductive (10 S/cm) tetrathiafulvalene-tetracyanoquinodimethane thin film electrodes that afford high performance organic transistors and inverters operating at low voltages.

Inorganic-organic hybrid TFTs have been fabricated at room temperature using IAD-derived high-quality semiconducting In₂O₃ and a crosslinked spin-coatable polymer gate dielectric. TFTs exhibiting field-effect mobilities up to 160 cm² V^–1 s^–1, on Si and 10 cm² V^–1 s^–1 on PET substrates have been demonstrated. TFTs on PET combine good transport characteristics as well as optical transparency and flexibility.

Molecular-acceptor doping of polythiophene results in high conductivity, ca. 1 S cm^–1, in solution-processed thin films. Charge-transfer complex formation leads to new hybrid orbitals (see figure), which are derived from the highest occupied level of the donor (polythiophene) and the lowest unoccupied level of the acceptor (tetrafluorotetracyanoquinodimethane).

A simple and versatile new method for fast micropatterning of conductive polymers has been demonstrated. Features sizes down to 2 μm have been realized in a conductive polymer (PEDOT) using a gel stamp impregnated with hypochlorite. The stamp is molded in bas-relief which enables spatially selective transfer of a chemical deactivation agent from the stamp to the conductive polymer in areas of contact.

Complex core/shell nanoparticles are synthesized with multiple rare-earth ions constrained to individual layers (see figure). A detailed analysis of the growth of the complex core/shell architectures through electron microscopy, X-ray analysis, and photoluminescence spectroscopy is presented. It is found that with controlled nucleation, a simple model can be used to predict the internal structure of the nanoparticles.

A novel complex nanostructure, produced by the directed assembly of a block copolymer thin film on chemically patterned surfaces, is presented. The new nanostructure, which consists of cylinders oriented alternately parallel and perpendicular to the surface (see figure, a result of self-consistent field calculations), demonstrates that a judiciously designed chemical pattern may be used to fabricate a well-ordered complex nanostructure in block copolymer thin films.

Photoluminescence decays from PbSe quantum dots (QDs) at different depths inside a 3D woodpile photonic crystal (PC) are investigated. The figure demonstrates that the average lifetimes of QDs with emitting wavelengths within the band gap region increase when the excitation position moves into the structure, indicating the inhibition of QD emission by the stop gap of the PC.

A room-temperature magnet of V[MeTCEC]₂·0.6(CH₂Cl₂) composition (MeTCEC = methyl tricyanoethylenecarboxylate) is formed by the reaction of MeTCEC and V(CO)₆ (see figure). Analysis of the magnetization indicates a less disordered structure of V[MeTCEC]₂·0.6(CH₂Cl₂) with respect to similarly synthesized V[TCNE]_x·0.34(CH₂Cl₂), presumably because of the much slower reaction of MeTCEC and V(CO)₆.

We demonstrate a new, flexible, one-step approach to direct the synthesis of FePt nanoparticle clusters or Fe₃O₄ nanoparticles, and their assembly into molecularly interconnected chains without the use of inorganic templates. The chain length as well as the diameter of the nanoparticle cluster can be varied by modifying the surfactants-precursor ratio.

Cationic polyfluorene colloids are prepared and adsorbed on cellulose to obtain fibers and paper sheets with high photoluminescence (see figure). The oxidative pretreatment of cellulose allows the tailoring of the fiber uptake capacity of polyfluorene colloids and the final photoluminescence intensity. Paper sheet strength is not affected by the adsorption of a sufficient amount of the colloid.

Fungal nanosynthesis of ternary CuAlO₂phase is achieved at 50 °C. This phase is chemically difficult to synthesize at low temperatures because of the incompatible oxidation chemistry of Cu and Al. The synthesized protein-capped water-dispersible nanoparticles show blue luminescence and radio-frequency absorption (see figure).

A self-releasing technique combining the catalytic growth of carbon nanotubes by chemical vapor deposition with an oxidation step is used to obtain ultrathick freestanding carbon nanotube films. Several millimeter thick films, such as the one depicted in the figure, are grown by controlling the gas flow rates and the catalyst deposition process. The freestanding nanotube films are used as supercapacitors and superhydrophobic surfaces.

With a facile one-pot strategy, up-conversion and down-conversion luminescent LaF₃ and NaLaF₄ nanorods are successfully prepared. Owing to their high up-conversion and down-conversion luminescence, ease of processing, and simple fabrication, these luminescent inorganic nanocrystals may find great potential applications in polymer-based devices.

A new conjugated polymer, LBPP-1, with an unusually low band-gap (ca. 1.0 eV) is presented. Light absorption and photovoltaic response up to 1200 nm in composites with a fullerene is demonstrated. Solar cell performance is presented and the polymer's suitability for photodetection in the infrared region is discussed.

Nitrogen K-shell near-edge X-ray absorption fine structure (NEXAFS) measurements have been used for the first time to demonstrate 1D alignment of cobalt phthalocyanine (CoPc) molecules inside carbon nanotubes (see figure), revealing a stacking order consistent with the metastable α-CoPc phase. In addition, transmission electron microscopy images show pristine nanotubes surfaces and near-optimal filling. The smallest internal diameter to host CoPc molecules is found to be 15 Å.

Poly(1,3-phenylene-5-phosphonic acid) is characterized by a high density of functional groups (less than 100 g/mol equivalent weight per proton), good thermo-oxidative stability up to at least 200 °C, the absence of a softening point, and a proton conductivity of more than 2 × 10^–3 S/cm between 110 °C and 160 °C under water vapor. Based on these properties, this polymer appears to be well suited as proton conducting component in polymer electrolyte membranes.

A bilayer organic field effect transistor (OFET) sensor utilizing a phenol functionalized molecule as a receptor layer, designed to enhance interaction with a target vapor dimethyl methylphosphonate (DMMP) is presented. The presence of this receptor layer is shown to enhance the sensing properties of the device, supporting the hypothesis that the phenolic receptor material is hydrogen bonding to the DMMP vapor molecules.

Double-walled SnO₂nano-cocoons with movable α-Fe₂O₃cores have been prepared by hydrothermal shell-by-shell deposition of polycrystalline SnO₂ on ellipsoidal α-Fe₂O₃/SiO₂ core/shell nanotemplates followed by removal of SiO₂. The present templating approach also leads to two other nano-architectures, namely single-walled and porous double-shelled nano-cocoons. The α-Fe₂O₃ cores can be reduced to magnetic Fe₃O₄ post-synthesis.

The role of dislocations in stable p-type phosphorus-doped ZnO epitaxial films is investigated. It is shown that good p-type conductivity is always associated with a considerable increase in the density of dislocations, which can aid the formation of shallow complex acceptors and provide sinks for native donors.

A quasi-solid state dye-sensitized solar cell has been constructed by employing a nanocomposite organic-inorganic solid gel electrolyte. The titania film was a combination of nanoparticles of two distinct sizes obtained by separate sol-gel syntheses using different organic templates. The synergy between these entities raised cell efficiency to 6.9% under 1 sun. This value is very high, considering the fact that it is obtained with a quasi-solid state cell.

Confining surface-pinned micelles consisting of a block copolymer onto a topographically patterned substrate is demonstrated (see figure) with a novel approach to control both the local as well as global structural symmetry and periodicity of the self-assembled block copolymer. No surface micelles are confined into the dents at the position of 1a. The surface micelles formed with bimodal size distribution are assembled into two different tetragonal symmetries indicated by the solid and dotted lines, respectively.

SmCo₅magnets are synthesized by the facile Ca reduction of core/shell-structured Co/Sm₂O₃nanoparticles, as schematically illustrated in the figure. The magnets exhibit coercivities reaching 24 kOe at 100 K and 8 kOe at room temperature. The synthesis represents an important first step towards the fabrication of SmCo-based exchange-spring nanocomposites for high-performance permanent magnet applications.

Dopant-induced helical conformations of polyaniline (PANI) nanofibers are presented. Right- and left-handed helical nanofibers of conducting PANI are produced using respectively D- and L-camphorsulfonic acid as the dopant, it is reported, as proved by the mirror-image chiral dichroism spectra (see figure). The authors suggest a mechanism for the formation of nanofibrillar bundles of helical nanofibers.

Improved electron transport along a carbon nanotube (CNT) fiber when it is spun from an array of longer nanotubes is reported. The effect of chemical post-treatments is also demonstrated. For example, the covalent bonding of gold nanoparticles to the CNT fibers remarkably improves conductivity (see figure), whereas annealing CNT fibers in a hydrogen-containing atmosphere leads to a dramatic decrease in conductivity.

Electrode material diffusion in polymer/nanoparticle composite devices has been detected after the application of high electric fields (10⁷ V m^–1). Composition depth profiles obtained with SIMS show diffusion of material from both the aluminium cathode and the ITO anode. This diffusion can cause device failure even in low current regimes. The growth of the aluminium oxide is explained in terms of the Mott model.

A biomimetic cellulose I nanolayer with a parallel chain alignment was successfully designed through the chemoselective modification of cellulose and self-assembly of its thiosemicarbazone on a gold substrate (see figure). This is the first time replication of the crystalline structure of native cellulose, that is, cellulose I, in the layer state has been achieved.

Quantum dot light-emitting diodes with high external quantum efficiency and luminous power efficiency are realized through in situ thermal annealing of a quasi-monolayer of colloidal nanocrystals on a crosslinked hole-transport layer. Partial desorption of quantum-dot surface ligands and improved film morphology contribute to better electrical injection from the organic layers to the quantum dots, resulting in a 3 to 4 fold enhancement of device efficiency with emission exclusively from the quantum dots.

A protein-based dynamic hydrogel was generated via photo-crosslinking of an engineered protein-polymer conjugate. The protein calmodulin was used in this study due to its pronounced hinge motion in the presence of a variety of ligands. The resulting hydrogel is capable of undergoing substantial (>65%) and controllable volume transitions in the presence of calmodulin ligands, and the change can be attributed to a shift in protein conformation upon ligand binding.

A series of functionalized pentacene derivatives based on symmetric and asymmetric substitutions of the terminal rings are synthesized (see figure). Field-effect mobilities as high as 0.23 cm² V^–1 s^–1 are obtained with 2,3-dibrompentacene. These devices show improved stability compared to pentacene and exhibit no significant decrease in mobility or on/off ratio when stored in air, with and without light exposure, even after three months.

The shape-controlled synthesis of Pd nanostructures is featured in this Research News article. A number of useful parameters can be tuned to control the formation of Pd nanostructures with a specific shape in a solution-phase synthesis are discussed. The ability to control the shape provides an opportunity to systematically evaluate electrical, plasmonic, and catalytic properties as well as to fully explore applications of Pd nanostructures.