Advanced Functional Materials

Organic resistive memory has been extensively investigated as a promising memory technology due to technical advantages such as its simple structure, low fabrication cost, and printing applicability as well as exceptional memory performances. In their Feature Article, on page 2806, Takhee Lee and co-workers focus in particular on important strategies to implement more practical memory applications in terms of performance, integration, and architectures.

The implementation of engineered surfaces with micrometer-sized patterns of cell adhesive ligands against a biologically inert background has led to numerous discoveries in fundamental cell biology. On page 2876, Jennifer L. West and co-workers present a laser-based patterning strategy for the fabrication of surfaces displaying multiple patterned ligands, where each ligand is confined to its own array. Cells cultured on surfaces with two ligands display concurrent adhesion to both ligands simultaneously and utilize both ligands for lamella formation during migration.

Recently, organic resistive memory devices, which have many advantages including simple device structures, low fabrication costs, and printability, have been extensively investigated. The focus of this Feature Article is on essential strategies for memory performance enhancement, high-density integration, and advanced architectural concepts necessary for future memory applications.

With a PEG-based gel serving as a 3D scaffold, the strong fluorescence of semiconductor quantum dots and the plasmonics of metallic gold are combined into a sub-100-nm thermosensitive nano-object for multiple functions: a high-resolution biosensor for temperature sensing over physiological ranges, a fluorescent agent for tumor-cell imaging, and a drug carrier for synergistic chemo-photothermal treatment. This results in a nanoplatform that can execute diagnosis, therapy, and monitoring simultaneously.

The reversible displacement reaction of a MoS₂/PEO/graphene nanocomposite with lithium was systematically investigated. Crystalline Li₂S and amorphous Mo formed during electrochemical lithiation. The incorporation of PEO stabilizes the reversibility of the reaction and contributes to increased ionic conductivity. The irreversible reduction of Mo⁴⁺ to Mo nanoparticles along with the addition of graphene improves the electronic conductivity of the nanocomposite allowing for high rate cycling. The mechanism provides insight into the activation and design of high-performance electrode materials for energy storage.

A microfluidic chip that incorporates colloidal crystals inside a microchannel system for online analysis is demonstrated. Colloidal crystals with varying filtering effects have been integrated into lab-on-a-chip devices to locally enable the selective transmission or blocking of a particular range of wavelengths. Combined double-band colloidal crystals enable further tunability of the stop bands for filtering applications.

A novel organic light-emitting field-effect transistors is presented, consisting of bilayer-crystal organic semiconductors of a p-type and an n-type. In the devices, we observe strong emissions with maximum emission intensities that are larger by hundred times than those of single-layer crystal devices of each type. Emissions come from both of the crystals. The external quantum efficiency of the bilayer devices reaches 0.045%.

A biohybrid hydrogel is synthesized for the drug-inducible release of biopharmaceuticals. The hydrogel consists of linear polyacrylamide crosslinked by the interaction of the tetracycline repressor scTetR with its target DNA sequence tetO. Addition of tetracycline dissociates the protein-DNA interaction and triggers the release of a previously embedded payload protein.

A conductive multi-catalyst system consisting of Fe₃O₄ magnetic nano-particles (MNPs) and oxidative enzyme co-entrapped in the pores of mesoporous carbon is developed as an efficient and robust electrochemical biosensing platform. Immobilized MNPs in MSU-F-C show a high catalytic efficiency as peroxidase and enable the rapid detection of hydrogen peroxide and phenolic compounds.

A laser-based patterning strategy for the fabrication of multifaceted, micropatterned surfaces that display patterned arrays of multiple cell adhesive ligands with each ligand confined to its own array is presented. Cells cultured on these surfaces display concurrent adhesion to both ligands simultaneously and utilize both ligands for lamella formation during migration.

Genetically engineered spider silk was modified to incorporate a short peptide sequence to nucleate silver ions. The resulting hybrid protein combines the strength and biocompatibility of silk with nucleation of silver ions for antimicrobial functions. The table of contents figure shows: a) silver nanoparticles formed on the surface of the silk protein, b) inhibition of microbial growth.

The first use of carbazolyl thiol SAM to modify Au electrode is reported. Luminescent electropolymerization (EP) films are then grafted onto the electrode to prepare highly efficient and stable EP devices. The electroactive SAM can enhance the work function of the electrode and promote the cross-linking efficiency and the adhesion of EP films. This simple approach has potential applications in display devices.

Thickness-dependent measurements of lithium fluoride thin films grown on c-plane sapphire substrates allow the separation of bulk and interface conductions. The normalized conductance decreases linearly with decreasing LiF layer thickness with a negative extrapolated intercept. It indicates depletion of lithium ion vacancies as majority charge carriers and hence a negative space-charge potential. A generalized Mott–Schottky approach within the model of heterogeneous doping fully explains the entire boundary defect chemistry.

Sustained release and bone regeneration: Solid free-form fabrication of tissue- engineering scaffold is successfully carried out with a poly(lactic-co-glycolic acid) grafted hyaluronic acid (HA-PLGA) conjugate encapsulating an intact bone morphogenetic protein–2/poly(ethylene glycol) (BMP-2/PEG) complex. In vitro release tests confirm the sustained release of intact BMP-2 from the scaffolds for up to a month. Furthermore, microcomputed tomography and histological analysis reveal effective bone regeneration on the HA-PLGA/PEG/BMP-2 scaffolds implanted into calvarial bone defects of Sprague Dawley rats.

Flexural–torsional oscillations consisting of in-plane bending and out-of-plane twisting are observed in cantilevers composed of monodomain, photoresponsive liquid crystal polymers with the nematic director offset at intermediate angles to the long axis of the cantilever.

A new cell-exclusion patterning technique is presented by Shuichi Takayama and co-workers on page 2920. Rehydration of dried polymeric aqueous two-phase systems results in well-defined cell-excluded circular gaps within a cell monolayer to serve as a migration niche for cells. The utility of this approach is demonstrated for high-throughput quantitative cancer-cell migration studies.

Utilizing rehydration of dried polymeric aqueous two-phase systems, well-defined cell-excluded circular gaps are patterned within a cell monolayer to serve as migration niche for cells. The utility of this approach is demonstrated for high throughput quantitative cancer cell migration studies.

A new model to interpret the anisotropic sliding behavior of the rice leaf is proposed based on three-level microstructures (macrogrooves, micropapilla, and nanostructures). The three-level hierarchical surfaces were reproduced by combining photolithography, PDMS imprinting, and micro/nanostructure coating, and a new method was developed, named curvature-assisted droplet oscillation (CADO), to quantitatively characterize the weak frictional interaction between the liquid droplet and the structured surface.

Single-electron tunneling via molecular quantum dots is successfully demonstrated in a practical device configuration of a metal-insulator-semiconductor structure. The phenomenon is observable up to 280 K, which is almost room temperature. Based on these attractive features, our device can be regarded as a prototype device for “More than Moore”, in which molecular functionalities can be integrated into Si-based devices.

A streptavidin-functionalized silver-nano-particle-enriched carbon nanotube is designed as a trace tag for ultrasensitive multiplexed detection of tumor markers by combination with silver-deposition enhancement and electrochemical stripping analysis of silver nanoparticles on a disposable immunosensor array. The excellent analytical performance of this method demonstrates that the functionalized nanohybrid is a promising and versatile amplified probe for application in biotechnology.

Organic dye sensitizers D35 and M14 have been employed in both liquid and solid state DSCs. This study shows that careful modifications in dye structure with high extinction coefficient as well as suitable surface blocking behavior will lead to more efficient sensitizers for DSCs.

Plastic surgery on the nanoscale: Functionalized pockets inside the pore walls of periodically ordered mesoporous organosilicas can be created by the scission of ethylene-containing bridging groups. However, one needs to be highly aware of the influence of the inorganic matrix. An in situ solid-state NMR spectroscopy study showed that total amputation resulting in a topotactic transformation is caused by the α-silicon effect.

A novel hybrid resist based on the thiol–ene photopolymerization is presented here. Our system is comprised of mercaptopropyl polyhedral oligomeric silsesquioxane and benzyl methacrylate, with trimethylolpropane trimethacrylate as the crosslinker. The obtained hybrid resists possess a variety of characteristics desirable for UV nanoimprint lithography, such as low viscosity, low bulk-volumetric shrinkage, high Young's modulus, high thermal stability, and excellent dry-etch resistance.

Control of the amorphous state by serum proteins is essential for homeostasis and mineralization processes in vivo. For the first time, the ability of the three most abundant serum proteins to stabilise the amorphous state of three key calcium biominerals is compared. Their effect on the formation of functional nanostructured gold particles that can be used as a biosensing device is also investigated.

Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of ultralarge graphene oxide sheets (with an aspect ratio of over 30 000) to water above a critical concentration of about 0.1 wt%. Self-assembled, free-standing GO papers with a highly aligned layered structure are fabricated by simple casting of graphene oxide liquid-crystal dispersions.

A new one-step electrochemical synthesis of graphene/polyaniline composite films was developed using graphite oxide and aniline as the starting materials. Horseradish peroxidase was entrapped onto the film-modified electrode and used to construct a H₂O₂ biosensor. A supercapacitor was also fabricated based on the composite film.