Local pH-Responsive Diazoketo-Functionalized Photoresist for Multicomponent Protein Patterning

Selective surface immobilization of multiple biomolecule components, under mild conditions where they do not denature, is attractive for applications in biosensors and biotechnology. Here, we report on a biocompatible and pH-responsive photoresist containing diazoketo-functionalized methacrylate, methacrylic acid, and poly­(ethylene glycol) methacrylate monomers, where the photolithographic process may be carried out in a local pH range to minimize biomolecular denaturation. The polymer is insoluble or sparsely soluble in pH 6.4 or more acidic solution or deionized water, but soluble in a basic solution, pH 7.9 or more. After UV exposure, however, carboxylic acid groups are generated by Wolff rearrangement and photodissociation of the diazoketo groups in the polymer chain, leading to dissolution of UV-exposed polymer at pH 6.4. Using the property of the pH-solubility switching, we demonstrate dual streptavidin patterning using only biological buffers, pH 6.4 and 7.9 solutions, and double exposure patterning to confirm the sustainability of the diazoketo groups in unexposed regions despite carrying out several wet processes

Polycrystalline and Mesoporous 3‑D Bi₂O₃ Nanostructured Negatrodes for High-Energy and Power-Asymmetric Supercapacitors: Superfast Room-Temperature Direct Wet Chemical Growth

Superfast (≤10 min) room-temperature (300 K) chemical synthesis of three-dimensional (3-D) polycrystalline and mesoporous bismuth­(III) oxide (Bi₂O₃) nanostructured negatrode (as an abbreviation of negative electrode) materials, viz., coconut shell, marigold, honey nest cross section and rose with different surface areas, charge transfer resistances, and electrochemical performances essential for energy storage, harvesting, and even catalysis devices, are directly grown onto Ni foam without and with poly­(ethylene glycol), ethylene glycol, and ammonium fluoride surfactants, respectively. Smaller diffusion lengths, caused by the involvement of irregular crevices, allow electrolyte ions to infiltrate deeply, increasing the utility of inner active sites for the following electrochemical performance. A marigold 3-D Bi₂O₃ electrode of 58 m²·g^–1 surface area has demonstrated a specific capacitance of 447 F·g^–1 at 2 A·g^–1 and chemical stability of 85% even after 5000 redox cycles at 10 A·g^–1 in a 6 M KOH electrolyte solution, which were higher than those of other morphology negatrode materials. An asymmetric supercapacitor (AS) device assembled with marigold Bi₂O₃ negatrode and manganese­(II) carbonate quantum dots/nickel hydrogen–manganese­(II)–carbonate (MnCO₃QDs/NiH–Mn–CO₃) positrode corroborates as high as 51 Wh·kg^–1 energy at 1500 W·kg^–1 power and nearly 81% cycling stability even after 5000 cycles. The obtained results were comparable or superior to the values reported previously for other Bi₂O₃ morphologies. This AS assembly glowed a red-light-emitting diode for 20 min, demonstrating the scientific and industrial credentials of the developed superfast Bi₂O₃ nanostructured negatrodes in assembling various energy storage devices

Enhancing the Directed Self-assembly Kinetics of Block Copolymers Using Binary Solvent Mixtures

The rapid pattern formation of well-ordered block copolymer (BCP) nanostructures is practical for next-generation nanolithography applications. However, there remain critical hurdles to achieve the rapid self-assembly of BCPs with a high Flory–Huggins interaction parameter (χ), owing to their slow kinetics. In this article, we report that a binary solvent vapor annealing methodology can significantly accelerate the self-assembly kinetics of poly­(dimethylsiloxane-<i>b</i>-styrene) (PDMS-<i>b</i>-PS) BCPs with a high-χ. In particular, we systemically analyzed the effects of the mixing ratio of a binary solvent composed of a PDMS-selective solvent (heptane) and a PS-selective solvent (toluene), showing an ultrafast self-assembly time (≤1 min) to obtain a well-ordered nanostructure. Moreover, we successfully accomplished extremely fast generation of sub-20 nm dot patterns within an annealing time of 10 s in a 300 nm-wide trench by means of binary solvent annealing. We believe that these results are also applicable to other solvent-based annealing systems of BCPs and that they will contribute to the realization of next-generation ultrafine lithography applications

Annealing environment effects on the electrochemical behavior of supercapacitors using Ni foam current collectors

Nickel (Ni) foam-based symmetric/asymmetric electrochemical supercapacitors benefit from a randomly 3D structured porous geometry that functions as an active material support and as a current collector. The surface composition stability and consistency of the current collector is critical for maintaining and consistency supercapacitor response, especially for various mass loading and mass coverage. Here we detail some annealing environment conditions that change the surface morphology, chemistry and electrochemical properties of Ni foam by NiO formation. Air-annealing at 400 and 800 °C and annealing also in N2 and Ar at 800 °C result in the in situ and ex situ formation of NiO on the Ni foam (NiO@Ni). Oxidation of Ni to NiO by several mechanisms in air and inert atmospheres to form a NiO coating is subsequently examined in supercapacitors, where the electrochemical conversion through Ni(OH)2 and NiOOH phases influence the charge storage process. In parallel, the grain boundary density reduction by annealing improves the electronic conductivity of the foam current collector. The majority of stored charge occurs at the oxidized Ni-electrolyte interface. The changes to the Ni metal surface that can be caused by chemical environments, heating and high temperatures that typically occur when other active materials are grown on Ni directly, should be considered in the overall response of the electrode, and this may be general for metallic current collectors and foams that can oxidize at elevated temperatures and become electrochemically active

Two-Minute Assembly of Pristine Large-Area Graphene Based Films

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2–3 layer pristine graphene platelets temporally solvated with <i>N</i>-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility

Complementary p- and n‑Type Polymer Doping for Ambient Stable Graphene Inverter

Graphene offers great promise to complement the inherent limitations of silicon electronics. To date, considerable research efforts have been devoted to complementary p- and n-type doping of graphene as a fundamental requirement for graphene-based electronics. Unfortunately, previous efforts suffer from undesired defect formation, poor controllability of doping level, and subtle environmental sensitivity. Here we present that graphene can be complementary p- and n-doped by simple polymer coating with different dipolar characteristics. Significantly, spontaneous vertical ordering of dipolar pyridine side groups of poly(4-vinylpyridine) at graphene surface can stabilize n-type doping at room-temperature ambient condition. The dipole field also enhances and balances the charge mobility by screening the impurity charge effect from the bottom substrate. We successfully demonstrate ambient stable inverters by integrating p- and n-type graphene transistors, which demonstrated clear voltage inversion with a gain of 0.17 at a 3.3 V input voltage. This straightforward polymer doping offers diverse opportunities for graphene-based electronics, including logic circuits, particularly in mechanically flexible form

Two-Minute Assembly of Pristine Large-Area Graphene Based Films

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2–3 layer pristine graphene platelets temporally solvated with <i>N</i>-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility

Biomineralized N-Doped CNT/TiO₂ Core/Shell Nanowires for Visible Light Photocatalysis

We report an efficient and environmentally benign biomimetic mineralization of TiO₂ at the graphitic carbon surface, which successfully created an ideal TiO₂/carbon hybrid structure without any harsh surface treatment or interfacial adhesive layer. The N-doped sites at carbon nanotubes (CNTs) successfully nucleated the high-yield biomimetic deposition of a uniformly thick TiO₂ nanoshell in neutral pH aqueous media at ambient pressure and temperature and generated N-doped CNT (NCNT)/TiO₂ core/shell nanowires. Unlike previously known organic biomineralization templates, such as proteins or peptides, the electroconductive and high-temperature-stable NCNT backbone enabled high-temperature thermal treatment and corresponding crystal structure transformation of TiO₂ nanoshells into the anatase or rutile phase for optimized material properties. The direct contact of the NCNT surface and TiO₂ nanoshell without any adhesive interlayer introduced a new carbon energy level in the TiO₂ band gap and thereby effectively lowered the band gap energy. Consequently, the created core/shell nanowires showed a greatly enhanced visible light photocatalysis. Other interesting synergistic properties such as stimuli-responsive wettabilites were also demonstrated