Bolometric IR photoresponse based on a 3D micro-nano integrated CNT architecture

A new 3D micro-nano integrated M-shaped carbon nanotube (CNT) architecture was designed and fabricated. It is based on vertically aligned carbon nanotube arrays composed of low-density, mainly double-walled CNTs with simple lateral external contacts to the surroundings. Standard optical lithography techniques were used to locally tailor the width of the vertical block structure. The complete sensor system, based on a broadband blackbody absorber region and a high-resistance thermistor region, can be fabricated in a single chemical vapor deposition process step. The thermistor resistance is mainly determined by the high junction resistances of the adjacent aligned CNTs. This configuration also provides low lateral thermal conductivity and a high temperature coefficient of resistance (TCR). These properties are advantageous for new bolometric sensors with high voltage responsivity and broadband absorption from the infrared (IR) to the terahertz spectrum. Preliminary performance evaluations have shown current and voltage responsivities of 2 mA/W and 30 V/W, respectively, in response to IR (980 nm) absorption for a 20 × 20 μm2 device. The device exhibits an exceptionally fast response time of ≈0.15 ms, coupled with a TCR of -0.91 %/K. These attributes underscore its high operating speed and responsivity, respectively. In particular, the device maintains excellent thermal stability and reliable operation at elevated temperatures in excess of 200 °C, extending its potential utility in challenging environmental conditions. This design allows for further device miniaturization using optical lithography techniques. Its unique properties for mass production through large-scale integration techniques make it important for real-time broadband imaging systems.

Nanomaterials revolutionize biosensing: 0D-3D designs for ultrasensitive detection of microorganisms and viruses

Various diseases caused by harmful microorganisms and viruses have caused serious harm and huge economic losses to society. Thus, rapid detection of harmful microorganisms and viruses is necessary for disease prevention and treatment. Nanomaterials have unique properties that other materials do not possess, such as a small size effect and quantum size effect. Introducing nanomaterials into biosensors improves the performance of biosensors for faster and more accurate detection of microorganisms and viruses. This review aims to introduce the different kinds of biosensors and the latest advances in the application of nanomaterials in biosensors. In particular, this review focuses on describing the physicochemical properties of zero-, one-, two-, and three-dimensional nanostructures as well as nanoenzymes. Finally, this review discusses the applications of nanobiosensors in the detection of microorganisms and viruses and the future directions of nanobiosensors.

Significant enhancement in the cold emission characteristics of chemically synthesized super-hydrophobic zinc oxide rods by nickel doping

The current article presents a huge enhancement in the field emission characteristics of zinc oxide (ZnO) micro/nanorods by nickel doping. The synthesis of pure and nickel-doped zinc oxide (ZnO) micro/nanorods was done by a simple low-temperature chemical method. Both the as-prepared pure and doped samples were analyzed by X-ray diffraction and electron microscopy to confirm the proper phase formation and the developed microstructure. UV-vis transmittance spectra helped in determining the band gap of the samples. Fourier-Transform Infrared Spectroscopy (FTIR) spectra showed the different bonds present in the sample, whereas X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of nickel in the doped sample. Photoluminescence (PL) spectra showed that after doping, the band-to-band transition was affected, whereas defect-induced transition had increased significantly. After the nickel doping, contact angle measurement revealed a significant decrease in the sample's surface energy, leading to a remarkably high water contact angle (within the superhydrophobic region). Simulation through ANSYS suggested that the doped sample has the potential to function as an efficient cold emitter, which was also verified experimentally. The cold emission characteristics of the doped sample showed a significant improvement, with the turn-on field (corresponding to J = 1 μA cm-2) reduced from 5.34 to 2.84 V μm-1. The enhancement factor for the doped sample reached 3426, approximately 1.5 times higher compared to pure ZnO. Efforts have been made to explain the results, given the favorable band bending as well as the increased number of effective emission sites.

Three-Dimensional Electrochemical Sensors for Food Safety Applications

Considering the increasing concern for food safety, electrochemical methods for detecting specific ingredients in the food are currently the most efficient method due to their low cost, fast response signal, high sensitivity, and ease of use. The detection efficiency of electrochemical sensors is determined by the electrode materials' electrochemical characteristics. Among them, three-dimensional (3D) electrodes have unique advantages in electronic transfer, adsorption capacity and exposure of active sites for energy storage, novel materials, and electrochemical sensing. Therefore, this review begins by outlining the benefits and drawbacks of 3D electrodes compared to other materials before going into more detail about how 3D materials are synthesized. Next, different types of 3D electrodes are outlined together with common modification techniques for enhancing electrochemical performance. After this, a demonstration of 3D electrochemical sensors for food safety applications, such as detecting components, additives, emerging pollutants, and bacteria in food, was given. Finally, improvement measures and development directions of electrodes with 3D electrochemical sensors are discussed. We think that this review will help with the creation of new 3D electrodes and offer fresh perspectives on how to achieve extremely sensitive electrochemical detection in the area of food safety.

Recent Advances in Synthesis and Application of Metal Oxide Nanostructures in Chemical Sensors and Biosensors

Nanostructured materials formed from metal oxides offer a number of advantages, such as large surface area, improved mechanical and other physical properties, as well as adjustable electronic properties that are important in the development and application of chemical sensors and biosensor design. Nanostructures are classified using the dimensions of the nanostructure itself and their components. In this review, various types of nanostructures classified as 0D, 1D, 2D, and 3D that were successfully applied in chemical sensors and biosensors, and formed from metal oxides using different synthesis methods, are discussed. In particular, significant attention is paid to detailed analysis and future prospects of the synthesis methods of metal oxide nanostructures and their integration in chemical sensors and biosensor design.

In Situ One-Pot Synthesis of C-Decorated and Cl-Doped Sea-Urchin-like Rutile Titanium Dioxide with Highly Efficient Visible-Light Photocatalytic Activity

Titanium dioxide (TiO₂) that offers high light-harvesting capacity and efficient charge separation holds great promise in photocatalysis. In this work, an in situ one-pot hydrothermal synthesis was explored to prepare a C-decorated and Cl-doped sea-urchin-like rutile TiO₂ (Cl-TiO₂/C). The growth of sea-urchin-like 3D hierarchical nanostructures was governed by a mechanism of nucleation and nuclei growth-dissolution-recrystallization growth from time-dependent morphology evolution. The crystal morphology and the content of Cl and C could be controlled by the volume ratio of HCl to TBOT. Systematic studies indicated that the 0.4Cl-TiO₂/C sample (the volume ratio of HCl to TBOT was 0.4) exhibited the highest visible-light photocatalytic activity for the degradation of rhodamine B, with kinetic rate constant (k) of 0.0221 min^-1, being 6.5 and 3.75 times higher than that of TiO₂ and Cl-TiO₂. The enhanced photocatalytic performance could be attributed to the high charge separation and transfer efficiency induced by Cl-doping and C decoration and the excellent light-harvesting capacity caused by its sea-urchin-like nanostructure. Moreover, the 0.4Cl-TiO₂/C sample exhibited good reusability and excellent structural stability for five cycles. This facile one-pot approach provides new insight for the preparation of a TiO₂-based photocatalyst with excellent photocatalytic performance for potential application in practical wastewater treatment.

The establishment of an immunosensor for the detection of SPOP

In this paper, we first synthesis three-dimensional jasmine-like Cu@L-aspartic acid(L-ASP) inorganic–organic hybrid nanoflowers to load palladium-platinum nanoparticles (Pd–Pt NPs) as the signal enhancer in order to quantify intracellular speckle-type POZ domain protein. Scanning electron microscope, fourier transform infrared, energy dispersive spectrometer, X-ray photoelectron spectroscopy analysis was used to characterize the newly synthesized materials. The newly formed Cu@L-Asp/Pd-PtNPs can catalyze the decomposition of hydrogen peroxide and exhibit excellent catalytic performance. When different concentration of speckle-type POZ domain protein is captured by speckle-type POZ domain protein antibody linked to the surface of Cu@L-Asp/Pd–Pt NPs, the current signal decreases with the increase concentration of speckle-type POZ domain protein. After optimization, the speckle-type POZ domain protein immunosensor exhibited a good linear response over a concentration range from 0.1–1 ng mL⁻¹ with a low detection limit of 19 fg mL⁻¹. The proposed sensor demonstrates good stability within 28 days, acceptable reproducibility (RSD = 0.52%) and selectivity to the speckle-type POZ domain protein in the presence of possible interfering substances and has potential application for detecting other intracellular macromolecular substances.

One-dimensional assembly of β-form anhydrous guanine microrods

Biogenic guanine crystals exhibit excellent optical properties owing to their extremely high refractive index. However, there is no report related to the highly-ordered guanine assemblies in the synthetic systems. Herein, β-phase anhydrous guanine (β-AG) microrods were formed in mixed solvents of formamide and water in the presence of small organic molecules such as uric acid, pyrrole (Py), N-methyl-2-pyrrolidone (NMP), N-vinyl-2-pyrrolidone (NVP). The one-dimensional (1D) assembly of β-AG microrods form spontaneously in water, which is the first reported highly ordered 1D assembly of organic micro- or nanocrystals in the solution. The obtained β-AG microrods obtained in Py system can form reversible 1D assembly in water after being treated in organic solvents such as ethanol, acetone and isopropanol, which have high solubility in water. However, no reversible 1D assembly but only dispersed or aggregated guanine microrods formed in water after similar treatment in the other three organic solvents such as n-hexane, dichloroethane and petroleum ether with low solubility in water. Similar reversible assembly features can also be observed in other three systems, standard system, and NVP and NMP systems. The reversible 1D assemblies of guanine microrods in water and organic solvents with high solubility in water indicate that there is a strong interaction between the (100) planes of β-AG microrods in water. The oriented 1D assembly of guanine microrods with long axes perpendicular to the horizontal magnetic field can form in water under magnetic field.

Enticing 3D peony-like ZnGa2O4 microstructures for electrochemical detection of N, N-dimethylmethanamide chemical

We demonstrate the hydrothermal synthesis of three dimension (3D) peony-like morphology of zinc gallate (ZnGa₂O₄), dominated by assembled nanosheets and applied as electrode material in electrochemical detection of N,N-dimethylmethanamide chemical. The crystalline, structural and compositional characterizations deduced the formation of high quality ZnGa₂O₄ with spinal crystal structure. Peony-like 3D ZnGa₂O₄ was benefited by a high surface area of ~62.3 m² g^-1, good pore distribution (mean pore diameter of ~23.3 nm) and large pore volume of ~0.3622 cm³ g^-1. N,N-dimethylmethanamide chemical sensor based on peony-like 3D ZnGa₂O₄ electrode presented a linear curve in the working dynamic range of 1 nM-10 mM. Significantly improved chemical sensitivity of ~154.2 mA mM^-1 cm^-2 with low detection limit value of ~0.14 μM were achieved. The fabricated sensor based on peony-like 3D ZnGa₂O₄ electrode endorsed real sample analysis and ascertained the selectivity towards N,N-dimethylmethanamide chemical by analyzing a range of interfering analytes, viz. ethanol, tetrahydrofuran, methyl amine chemical.

Ternary MOF-on-MOF heterostructures with controllable architectural and compositional complexity via multiple selective assembly

Assembly of different metal-organic framework (MOF) building blocks into hybrid MOF-on-MOF heterostructures is promising in chemistry and materials science, however the development of ternary MOF-on-MOF heterostructures with controllable architectural and compositional complexity is challenging. Here we report the synthesis of three types of ternary MOF-on-MOF heterostructures via a multiple selective assembly strategy. This strategy relies on the choice of one host MOF with more than one facet that can arrange the growth of a guest MOF, where the arrangement is site-selective without homogenous growth of guest MOF or homogenous coating of guest on host MOF. The growth of guest MOF on a selected site of host MOF in each step provides the opportunity to further vary the combinations of arrangements in multiple steps, leading to ternary MOF-on-MOF heterostructures with tunable complexity. The developed strategy paves the way towards the rational design of intricate and unprecedented MOF-based superstructures for various applications.

A Peptide-Based Method for the Fabrication of 1D Rail-Like Nanoparticle Chains and 2D Nanoparticle Membranes: Higher-Order Self-Assembly

Functionalized histidine-rich peptide sequences were designed for the site-directed assembly of nanoparticles. TEM and AFM images shown that the peptides self-assembled into well-ordered nanofibrils at pH 7.2. The nanofibrils could lie parallel to one another and form membranes when the solution was acidic (pH 3.8) resulting from the hierarchical assembly of the nanofibrils in the direction of the peptide backbone. These peptide structures served as a template for nucleation and growth of Au nanocrystals. Further characterization showed that the Au nanocrystals grew on both sides of the nanofibrils, and a 1D system with a rail-like structure and a 2D membrane were synthesized after reduction with hydrazine hydrate at neutral and acidic pH values, respectively. The size and packing density of the Au nanocrystals were positively correlated with the incubation time of the Au ions. This approach can be extended further to the controlled synthesis of 1D and 2D architectures formed from metals, metal sulfides, and metal oxides in a low-cost and simple manner. Finally, the nanostructures could catalyze the reduction of p-nitrophenol with rate constants of 0.83±0.14 and 0.69±0.09 min^-1 for the 1D and 2D structures, respectively.

Nanofabrication within unimolecular nanoreactors

Nanoparticles (NPs) have been a research focus over the last three decades owing to their unique properties and extensive applications. It is crucial to precisely control the features of NPs including topology, architecture, composition, size, surface and assembly because these features will affect their properties and then applications. Ingenious nanofabrication strategies have been developed to precisely control these features of NPs, especially for templated nanofabrication within predesigned nanoreactors. Compared with conventional nanoreactors (hard templates and supramolecular nanoreactors), unimolecular nanoreactors exhibit (1) covalently stable nanostructures uninfluenced by environmental variations, (2) extensively regulated features of the structure including topology, composition, size, surface and valence due to the rapid development of polymer chemistry, and (3) effective encapsulation of abundant guests with or without strong interaction to achieve the function of loading, delivery and conversion of guests. Thus, unimolecular nanoreactors have shown fascinating prospects as templates for nanofabrication. Various NPs with expected topologies (sphere, rod, tube, branch, and ring), architectures (compact, hollow, core-shell, and necklace-like), compositions (metal, metal oxide, semiconductor, doping, alloy, silica, and composite), sizes (generally 1-100 nm), surface properties (hydrophilic, hydrophobic, reactivity, valence and responsivity) and assemblies (oligomer, chain, and aggregate) can be fabricated easily within reasonably designed unimolecular nanoreactors in a programmable way. In this review, we provide a brief introduction of the properties and types of unimolecular nanoreactors, a condensed summary of representative methodologies of nanofabrication within various unimolecular nanoreactors and a predicted outlook of the potential further developments of this charming nanofabrication approach.

Assembly of reduced graphene oxides into a three-dimensional porous structure via confinement within robust cellulose oligomer networks

The assembly of nanomaterials into a networked superstructure is a strategy used to construct macroscopic porous materials having the functional properties of nanomaterials. However, because nanomaterials generally prefer densely packed assembled states owing to their high surface energies, the construction of a fine porous structure is still a challenge. In this study, we demonstrate the assembly of reduced graphene oxides (rGOs) into a fine porous structure via confinement within robust cellulose oligomer networks. The confinement of rGOs within cellulose oligomer networks was achieved in one step via the enzymatic synthesis of cellulose oligomers. When the resultant cellulose oligomer gels confining rGOs were reduced by hydrogen iodide, the robust cellulose oligomer networks served as a confinement space for rGOs, preventing excessive aggregation of the rGOs and thus encouraging their assembly into a fine porous structure. Electrochemical measurements revealed that the porous rGO materials could act as electrode materials for supercapacitors. Our strategy based on simple physical confinement will allow for the creation of functional porous materials with excellent nanomorphologies from various nanomaterials.

Ce4+ as a facile and versatile surface modification reagent for templated synthesis in electrical applications

Surface modification for templated synthesis is crucial to achieving three-dimensional (3D) architectured materials for catalysis, photonics, energy storage, etc. However, the existing facile and versatile modification methods (e.g. with dopamine and catechol) generate modification layers that are unstable in harsh environments. These methods are thus unsuitable for electrical applications. Here we report that Ce4+ can act as an effective surface modification reagent for a broad range of substrates (chitinous butterfly wings, carbon paper, nickel foam, and polyethylene terephthalate planks) with various structural features owing to its strong oxidizing ability and Lewis acid nature. The modification yields discrete CeO2 seed layers on substrate surfaces in ca. 0.25-2 h, important for the subsequent conformal growth of CeO2 nanoparticles, Ni(OH)2 nanowires, FeOOH nanosheets, and WO3 nanosheets into 3D architectured materials. The conformally synthesized FeOOH on nickel foam (NF) yields an overpotential of 241 mV at 10 mA cm-1 for an oxygen evolution reaction. This value is comparable to a typical catalyst Ni(Fe)OOH-NF for which the Ni/Fe ratio must be well-optimized. This facile and versatile strategy might have broad applications in the conformal fabrication and application of 3D architectured materials, especially when applied in electrical applications of architectured materials (e.g. Li-ion battery).

Generalized Preparation of Two-Dimensional Quasi-nanosheets via Self-assembly of Nanoparticles

Two-dimensional (2D) nanomaterials are attracting increasing research interest because of their unique properties and promising applications. Here, we report a facile method to manipulate the assembly of nanoparticles (NPs) to fabricate free-standing 2D quasi-nanosheets. The as-generated 2D products are composed of few-layer NPs; that is, their thicknesses are only tens of nanometers but lateral dimensions could be up to several micrometers. Therefore, the novel structure was denoted as 2D "quasi-nanosheets (QNS)". Specifically, several types of building blocks could be assembled into 2D unary, binary, ternary, and even quaternary QNS by a universal procedure. The entire assembly process is carried out in solution and mediated simply by tuning the concentration of ligands surrounding the NPs. In contrast to traditional assembly techniques, even without any substrate or template, these QNS showed exceptionally high stability. They can remain intact for several days without any disassembly regardless of the solvent environment (e.g., water, ethanol, methanol, and hexane). In general, our method has effectively tackled several limitations associated with traditional assembly techniques and allows more freedom in manipulating assembly of NPs, which may hold great potential for future fabrication of 2D devices with rich functionalities.

Fluoropolymer-Containing Opals and Inverse Opals by Melt-Shear Organization

The preparation of highly ordered colloidal architectures has attracted significant attention and is a rapidly growing field for various applications, e.g., sensors, absorbers, and membranes. A promising technique for the preparation of elastomeric inverse opal films relies on tailored core/shell particle architectures and application of the so-called melt-shear organization technique. Within the present work, a convenient route for the preparation of core/shell particles featuring highly fluorinated shell materials as building blocks is described. As particle core materials, both organic or inorganic (SiO₂) particles can be used as a template, followed by a semi-continuous stepwise emulsion polymerization for the synthesis of the soft fluoropolymer shell material. The use of functional monomers as shell-material offers the possibility to create opal and inverse opal films with striking optical properties according to Bragg’s law of diffraction. Due to the presence of fluorinated moieties, the chemical resistance of the final opals and inverse opals is increased. The herein developed fluorine-containing particle-based films feature a low surface energy for the matrix material leading to good hydrophobic properties. Moreover, the low refractive index of the fluoropolymer shell compared to the core (or voids) led to excellent optical properties based on structural colors. The herein described fluoropolymer opals and inverse opals are expected to pave the way toward novel functional materials for application in fields of coatings and optical sensors.

Fabrication of pioneering 3D sakura-shaped metal-organic coordination polymers Cu@L-Glu phenomenal for signal amplification in highly sensitive detection of zearalenone

Low molecular weight pollutants from foods have aroused global attention due to their toxicity after long-time exposure. There is an increased demand for appropriate methods to detect these pollutants in foods. In this study, a brand-new type of nano metal-organic coordination polymers (MOCPs) nanocarriers (3D sakura-shaped copper (II) ions@L-glutamic acid (L-Glu)) has been first synthesized. We herein demonstrate a facile chelated method that allows the combination of copper (II) ions and L-Glu. A series of controlled experiments have revealed that the reaction time and the ratio of reactants played the crucial roles in affecting the morphology of the final product. 3D sakura-shaped Cu@L-Glu combined with palladium-platinum nanoparticle (Pd-PtNPs) to obtain Cu@L-Glu/Pd-PtNPs acting as the signal tag, which applied in electrochemical aptasensor for ultrasensitive detection of zearalenone (ZEN). A glassy carbon electrode was first modified with spherical Au-PANI-Au nanohybrids to enhance the conductivity and immobilize more amino modified ZEN aptamer. Cu@L-Glu/Pd-PtNPs were labeled with Complementary DNA (partial matching with ZEN aptamer) to form bioconjugates for signal amplification. After the hybridization reaction of ZEN aptamer and the bioconjugates, a significant electrochemical signal from the catalysis of H₂O₂ by Cu@L-Glu/Pd-PtNPs can be observed. ZEN competed with bioconjugates for binding to ZEN aptamer, resulting in decreased the electrochemical signal. Chronoamperometry was applied to record the final electrochemical signals. Under optimal conditions, the electrochemical aptasensor exhibited desirable sensitive detection of ZEN with a wide linearity ranging from 1 fg/mL to 100 ng/mL and a relatively low detection limit of 0.45 fg/mL (S/N = 3). Furthermore, the proposed electrochemical aptasensor shows excellent selectivity to the ZEN in the presence of possible interfering substances, and has potential application for ZEN detection in food samples.

POSS-Containing Polymethacrylates on Cellulose-Based Substrates: Immobilization and Ceramic Formation

The combination of cellulose-based materials and functional polymers is a promising approach for the preparation of porous, biotemplated ceramic materials. Within this study, cellulose substrates were functionalized with a surface-attached initiator followed by polymerization of (3methacryloxypropyl)heptaisobutyl-T8-silsesquioxane (MAPOSS) by means of surface-initiated atom transfer radical polymerization (ATRP). Successful functionalization was proven by infrared (IR) spectroscopy as well as by contact angle (CA) measurements. Thermal analysis of the polymer-modified cellulose substrates in different atmospheres (nitrogen and air) up to 600 °C led to porous carbon materials featuring the pristine fibre-like structure of the cellulose material as shown by scanning electron microscopy (SEM). Interestingly, spherical, silicon-containing domains were present at the surface of the cellulose-templated carbon fibres after further ceramisation at 1600 °C, as investigated by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) measurements.

High performance electronic devices based on nanofibers via a crosslinking welding process

Recently, metal oxide nanofibers fabricated by electrospinning have been considered as promising components for next-generation electronic devices. Unfortunately, the nanofiber-based electronic devices usually exhibited inferior electrical performance, due to the high contact resistance between the nanofibers and the inferior interfacial adhesion between the nanofibers and the substrate. In this report, an amine-hardened epoxy resin was selected as an adhesion agent to weld nanofiber junctions and improve the interfacial adhesion performance. It was confirmed that the physical properties of the nanofibers were greatly improved after the crosslinking welding process. Taking advantage of the welding process, field-effect transistors (FETs) based on In₂O₃ nanofiber networks (NFNs) with various nanofiber densities were integrated and investigated. It was found that the FETs based on In₂O₃ NFNs with a nanofiber density of 0.4 μm^-1 exhibited the optimal electrical performance. When high-k ZrO_x was integrated into the FETs as the dielectric layer, the FETs based on In₂O₃ NFNs/ZrO_x exhibited superior performance, including a μ_FE of 13.2 cm² V^-1 s^-1, an I_on/I_off of 10⁷, and an SS of 90 mV per decade. The crosslinking welding process is a simple, versatile and low-cost technique, which has great possibility for various applications.

Nanowire Assemblies for Flexible Electronic Devices: Recent Advances and Perspectives

The fabrication of nanowire (NW)-based flexible electronics including wearable energy storage devices, flexible displays, electrical sensors, and health monitors has received great attention both in fundamental research and market requirements in our daily lives. Other than a disordered state after synthesis, NWs with designed and hierarchical structures would not only optimize the intrinsic performance, but also create new physical and chemical properties, and integration of individual NWs into well-defined structures over large areas is one of the most promising strategies to optimize the performance of NW-based flexible electronics. Here, the recent developments and achievements made in the field of flexible electronics composed of integrated NW structures are presented. The different assembly strategies for the construction of 1D, 2D, and 3D NW assemblies, especially the NW coassembly process for 2D NW assemblies, are comprehensively discussed. The improvements of different NW assemblies on flexible electronics structure and performance are described in detail to elucidate the advantages of well-defined NW assemblies. Finally, a short summary and outlook for future challenges and perspectives in this field are presented.

Fabrication of Functional Polymer Structures through Bottom-Up Selective Vapor Deposition from Bottom-Up Conductive Templates

An electrically induced bottom-up process was introduced for the fabrication of multifunctional nanostructures of polymers. Without requiring complicated photolithography or printing techniques, the fabrication process first produced a conducting template by colloidal lithography to create an interconnected conduction pathway. By supplying an electrical charge to the conducting network, the conducting areas were enabled with a highly energized surface that generally deactivated the adsorbed reactive species and inhibited the vapor deposition of poly- p-xylylene polymers. However, the template allowed the deposition of ordered poly- p-xylylene nanostructures only on the confined and negative areas of the conducting template, in a relatively large centimeter-scale production. The wide selection of functionality and multifunctional capability of poly- p-xylylenes naturally rendered the synergistic and orthogonal chemical reactivity of the resulting nanostructures. With only a few steps, the construction of a nanometer topology with the functionalization of multiple chemical conducts can be achieved, and the selected deposition process represents a state-of-the-art nanostructure fabrication in a simple and versatile approach from the bottom up.

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21^st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.

Fabrication of Core-Shell Nanotube Array for Artificial Photosynthesis Featuring an Ultrathin Composite Separation Membrane

Macroscale arrays of cobalt oxide-silica core-shell nanotubes with high aspect ratio and ultrathin walls of less than 20 nm have been fabricated. The silica shells feature embedded oligo-para(phenylenevinylene) molecules for charge transport across the insulating silica layer, which is tightly controlled by their electronic properties. The assembly is based on the use of a sacrificial Si nanorod array template combined with atomic layer deposition, covalent anchoring of organic wire molecules, and dry cryo-etching. High-resolution TEM imaging of samples prepared by microtome affords structural details of single core-shell nanotubes. The integrity of silica-embedded organic wire molecules exposed to atomic layer deposition, thermal treatment, and harsh etching procedures is demonstrated by grazing angle ATR FT-IR, FT-Raman, and XPS spectroscopy. The inorganic oxide-based core-shell nanotubes with ultrathin gas-impermeable, proton-conducting silica shells functionalized by molecular wires enable complete nanoscale photosynthetic units for CO₂ reduction by H₂O under membrane separation. Arrays of massive numbers of such core-shell nanotube units afford a design that extends the separation of the incompatible H₂O oxidation and CO₂ reduction catalysis environments across the continuum of length scales from nanometers to centimeters.

A 3D Self-Shaping Strategy for Nanoresolution Multicomponent Architectures

3D printing or fabrication pursues the essential surface behavior manipulation of droplets or a liquid for rapidly and precisely constructing 3D multimaterial architectures. Further development of 3D fabrication desires a self-shaping strategy that can heterogeneously integrate functional materials with disparate electrical or optical properties. Here, a 3D liquid self-shaping strategy is reported for rapidly patterning materials over a series of compositions and accurately achieving micro- and nanoscale structures. The predesigned template selectively pins the droplet, and the surface energy minimization drives the self-shaping processing. The as-prepared 3D circuits assembled by silver nanoparticles carry a current of 208-448 µA at 0.01 V impressed voltage, while the 3D architectures achieved by two different quantum dots show noninterfering optical properties with feature resolution below 3 µm. This strategy can facilely fabricate micro-nanogeometric patterns without a modeling program, which will be of great significance for the development of 3D functional devices.

Terminating DNA Tile Assembly with Nanostructured Caps

Precise control over the nucleation, growth, and termination of self-assembly processes is a fundamental tool for controlling product yield and assembly dynamics. Mechanisms for altering these processes programmatically could allow the use of simple components to self-assemble complex final products or to design processes allowing for dynamic assembly or reconfiguration. Here we use DNA tile self-assembly to develop general design principles for building complexes that can bind to a growing biomolecular assembly and terminate its growth by systematically characterizing how different DNA origami nanostructures interact with the growing ends of DNA tile nanotubes. We find that nanostructures that present binding interfaces for all of the binding sites on a growing facet can bind selectively to growing ends and stop growth when these interfaces are presented on either a rigid or floppy scaffold. In contrast, nucleation of nanotubes requires the presentation of binding sites in an arrangement that matches the shape of the structure's facet. As a result, it is possible to build nanostructures that can terminate the growth of existing nanotubes but cannot nucleate a new structure. The resulting design principles for constructing structures that direct nucleation and termination of the growth of one-dimensional nanostructures can also serve as a starting point for programmatically directing two- and three-dimensional crystallization processes using nanostructure design.

Vertically Aligned Carbon Nanotubes as Platform for Biomimetically Inspired Mechanical Sensing, Bioactive Surfaces, and Electrical Cell Interfacing

Vertically aligned carbon nanotubes (VACNTs) are one dimensional carbon objects anchored atop of a solid substrate. They are geometrically fixed in contrast to their counterparts, randomly oriented carbon nanotubes (CNTs). In this progress report, the breadth in which these one dimensional, mechanically flexible, though robust and electrical conducting carbon nanostructures can be employed as functional material is shown and our research is put in perspective to work in the last five to ten years. The connection between the different areas touched in this report is the biomimetic-materials approach, which rely on the hairy morphology of VACNTs. These properties in connection with their electrical conductivity offer possibilities towards new functional features and applications of VACNTs. To appreciate the possibilities of biomimetic research with VACNTs, first their material characteristics are given to make the reader familiar with specific features of their synthesis, the peculiarities in arranging and controlling the morphology of CNTs in a vertical alignment as well as a current understanding of these properties on a microscopic basis. In doing so, similarities as well as differences, which offer new possibilities for biomimetic studies of VACNTS with respect to multiwalled randomly oriented CNTs, will become clear.

Morphology Transition Engineering of ZnO Nanorods to Nanoplatelets Grafted Mo8O23-MoO2 by Polyoxometalates: Mechanism and Possible Applicability to other Oxides

A new fundamental mechanism for reliable engineering of zinc oxide (ZnO) nanorods to nanoplatelets grafted Mo8O23-MoO2 mixed oxide with controlled morphology, composition and precise understanding of the nanoscale reaction mechanism was developed. These hybrid nanomaterials are gaining interest due to their potential use for energy, catalysis, biomedical and other applications. As an introductory section, we demonstrate a new expansion for the concept 'materials engineering' by discussing the fabrication of metal oxides nanostructures by bottom-up approach and carbon nanoparticles by top-down approach. Moreover, we propose a detailed mechanism for the novel phenomenon that was experienced by ZnO nanorods when treated with phosphomolybdic acid (PMA) under ultra-sonication stimulus. This approach is expected to be the basis of a competitive fabrication approach to 2D hybrid nanostructures. We will also discuss a proposed mechanism for the catalytic deposition of Mo8O23-MoO2 mixed oxide over ZnO nanoplatelets. A series of selection rules (SRs) which applied to ZnO to experience morphology transition and constitute Abdelmohsen theory for morphology transition engineering (ATMTE) will be demonstrated through the article, besides a brief discussion about possibility of other oxides to obey this theory.

Facile synthesis of ultrathin Ni-MOF nanobelts for high-efficiency determination of glucose in human serum

Ultrathin Ni-MOF nanobelts, [Ni₂₀(C₅H₆O₄)₂₀(H₂O)₈]·40H₂O(Ni-MIL-77 NBs), were synthesized by a facile one-pot solution process and can be used as an efficient catalyst electrode for glucose oxidation under alkaline conditions. Electrochemical measurements demonstrate that the NB/GCE, when used as a non-enzymatic glucose sensor, offers superior analytical performances with a wide linear range (from 1 μM to 500 μM), a low detection limit (0.25 μM, signal-to-noise = 3), and a response sensitivity of 1.542 μA mM^-1 cm^-2. Moreover, it can also be applied for glucose detection in human blood serum with the relative standard deviation (RSD) of 7.41%, showing the high precision of the sensor in measuring real samples.

Plasma assisted deposition of single and multistacked TiO2 hierarchical nanotube photoanodes

We present herein an evolved methodology for the growth of nanocrystalline hierarchical nanotubes combining physical vapor deposition of organic nanowires (ONWs) and plasma enhanced chemical vacuum deposition of anatase TiO₂ layers. The ONWs act as vacuum removable 1D and 3D templates, with the whole process occurring at temperatures ranging from RT to 250 °C. As a result, a high density of hierarchical nanotubes with tunable diameter, length and tailored wall microstructures are formed on a variety of processable substrates as metal and metal oxide films or nanoparticles including transparent conductive oxides. The reiteration of the process leads to the development of an unprecedented 3D nanoarchitecture formed by stacking the layers of hierarchical TiO₂ nanotubes. As a proof of concept, we present the superior performance of the 3D nanoarchitecture as a photoanode within an excitonic solar cell with efficiencies as high as 4.69% for a nominal thickness of the anatase layer below 2.75 μm. Mechanical stability and straightforward implementation in devices are demonstrated at the same time. The process is extendable to other functional oxides fabricated by plasma-assisted methods with readily available applications in energy harvesting and storage, catalysis and nanosensing.

Cell Guidance on Nanostructured Metal Based Surfaces

Metal surface nanostructuring to guide cell behavior is an attractive strategy to improve parts of medical implants, lab-on-a-chip, soft robotics, self-assembled microdevices, and bionic devices. Here, we discus important parameters, relevant trends, and specific examples of metal surface nanostructuring to guide cell behavior on metal-based hybrid surfaces. Surface nanostructuring allows precise control of cell morphology, adhesion, internal organization, and function. Pre-organized metal nanostructuring and dynamic stimuli-responsive surfaces are used to study various cell behaviors. For cells dynamics control, the oscillating stimuli-responsive layer-by-layer (LbL) polyelectrolyte assemblies are discussed to control drug delivery, coating thickness, and stiffness. LbL films can be switched "on demand" to change their thickness, stiffness, and permeability in the dynamic real-time processes. Potential applications of metal-based hybrids in biotechnology and selected examples are discussed.

Photochemical Activation of Electrospun In2O3 Nanofibers for High-Performance Electronic Devices

Electrospun metal oxide nanofibers have been regarded as promising blocks for large-area, low-cost, and one-dimensional electronic devices. However, the electronic devices based on electrospun nanofibers usually suffer from poor performance and inferior viability. Here, we report an efficient photochemical process using UV light generated by a high-pressure mercury lamp to promote the electrical performance of the nanofiber-based electronic devices. Such UV treatment can lead to strong photochemical activation of electrospun nanofibers, and therefore, a stable adherent nanofiber network and electronic-clean interface were formed. By use of UV treatment, high-performance indium oxide (In₂O₃) nanofiber based field-effect transistors (FETs) with highly efficient modulation of electrical characteristics have been successfully fabricated. To reduce the operating voltage and further improve the device performance, the In₂O₃ nanofiber FETs based on solution-processed high-k AlO_x dielectrics were integrated and investigated. The as-fabricated In₂O₃/AlO_x FETs exhibit superior electrical performance, including a high mobility of 19.8 cm² V^-1 s^-1, a large on/off current ratio of 10⁶, and high stability over time and cycling. The improved performance of the UV-treated FETs was further confirmed by the integration of the electrospun In₂O₃/AlO_x FETs into inverters. This work presents an important advance toward the practical applications of electrospun nanofibers for functional electronic devices.

Large-scale self-assembly of uniform submicron silver sulfide material driven by precise pressure control

The controllable self-assembly of nanosized building blocks into larger specific structures can provide an efficient method of synthesizing novel materials with excellent properties. The self-assembly of nanocrystals by assisted means is becoming an extremely active area of research, because it provides a method of producing large-scale advanced functional materials with potential applications in the areas of energy, electronics, optics, and biologics. In this study, we applied an efficient strategy, namely, the use of 'pressure control' to the assembly of silver sulfide (Ag₂S) nanospheres  with a diameter of approximately 33 nm into large-scale, uniform Ag₂S sub-microspheres with a size of about 0.33 μm. More importantly, this strategy realizes the online control of the overall reaction system, including the pressure, reaction time, and temperature, and could also be used to easily fabricate other functional materials on an industrial scale. Moreover, the thermodynamics and kinetics parameters for the thermal decomposition of silver diethyldithiocarbamate (Ag(DDTC)) are also investigated to explore the formation mechanism of the Ag₂S nanosized building blocks which can be assembled into uniform sub-micron scale architecture. As a method of producing sub-micron Ag₂S particles by means of the pressure-controlled self-assembly of nanoparticles, we foresee this strategy being an efficient and universally applicable option for constructing other new building blocks and assembling novel and large functional micromaterials on an industrial scale.

Free-Standing Networks of Core-Shell Metal and Metal Oxide Nanotubes for Glucose Sensing

Nanotube assemblies represent an emerging class of advanced functional materials, whose utility is however hampered by intricate production processes. In this work, three classes of nanotube networks (monometallic, bimetallic, and metal oxide) are synthesized solely using facile redox reactions and commercially available ion track membranes. First, the disordered pores of an ion track membrane are widened by chemical etching, resulting in the formation of a strongly interconnected pore network. Replicating this template structure with electroless copper plating yields a monolithic film composed of crossing metal nanotubes. We show that the parent material can be easily transformed into bimetallic or oxidic derivatives by applying a second electroless plating or thermal oxidation step. These treatments retain the monolithic network structure but result in the formation of core-shell nanotubes of altered composition (thermal oxidation: Cu₂O-CuO; electroless nickel coating: Cu-Ni). The obtained nanomaterials are applied in the enzyme-free electrochemical detection of glucose, showing very high sensitivities between 2.27 and 2.83 A M^-1 cm^-2. Depending on the material composition, varying reactivities were observed: While copper oxidation reduces the response to glucose, it is increased in the case of nickel modification, albeit at the cost of decreased selectivity. The performance of the materials is explained by the network architecture, which combines the advantages of one-dimensional nano-objects (continuous conduction pathways, high surface area) with those of a self-supporting, open-porous superstructure (binder-free catalyst layer, efficient diffusion). In summary, this novel synthetic approach provides a fast, scalable, and flexible route toward free-standing nanotube arrays of high compositional complexity.

Fabrication of a silica/titania hollow nanorod and its electroresponsive activity

In this study, a 1D oriented hollow SiO₂/TiO₂ (HST) rod-like material was successfully fabricated via a sequential combination of sol–gel use, TiO₂ incorporation, and a sonication-mediated etching and redeposition method.

Grand challenges for catalysis in the Science and Technology Roadmap on Catalysis for Europe: moving ahead for a sustainable future

This perspective discusses the general concepts that will guide future catalysis and related grand challenges based on the Science and Technology Roadmap on Catalysis for Europe prepared by the European Cluster on Catalysis.

Synthesis and magnetic properties of nanostructured metallic Co, Mn and Ni oxide materials obtained from solid-state metal-macromolecular complex precursors

Reaction of chitosan with metallic salts gives nanostructured Mn₂O₃, Co₃O₄ and NiO. Graphitic carbon is formed over the nanostructured oxides.