Nanorobots Constructed from Nanoclay: Using Nature to Create Self‐Propelled Autonomous Nanomachines

Self‐propelled, autonomous micro and nanomachines are at the forefront of current nanotechnology. These micro and nanodevices move actively to perform desired tasks, usually using chemical energy from their surrounding environment. Typically, these structures are fabricated via clean room or template‐based electrodeposition methodologies, which yield relatively low numbers of these devices. To utilize these machines in industrial‐scale operations, one would need an inexpensive fabrication route for mass production of nanomachines. The use of naturally occurring nanotubes, Halloysite nanoclay, to fabricate functional nanomotors in great quantities is demonstrated. These nanotubes can be mined in ton quantities and used as base for the fabrication of nanomachines. In addition, it is well known that the surface groups of Halloysite nanoclay bind strongly with heavy metals, which makes it potentially useful in environmental remediation.     

Plasmonic Self‐Propelled Nanomotors for Explosives Detection via Solution‐Based Surface Enhanced Raman Scattering

Nanomotors represent a class of artificial machines that span the chasm between molecular motors and bigger micromotors. Their importance lies in the fact that to effectively navigate and perform tasks in a biological environment without alerting the action of the immune system, the maximal size of the object has to be well below 200 nm. Fully nanosized gold/silver core/shell plasmonic nanomotors using the seeded growth wet chemical approach, which allows high scalability of synthesis of the nanomotors compared to planar substrate‐based methods, is presented. Using the nanoparticle tracking analysis, the catalysis driven enhanced diffusion of the plasmonic nanomotors in the presence of low concentrations of fuel is presented and shown that the prepared nanomotors are good candidates for a solution‐based surface‐enhanced Raman spectroscopy detection of picric acid, a typical explosive. In addition to the mentioned effects, ligand‐exchange is performed on the nanomotors to replace the surfactant with its thiolated analog, a combination which is already proven in literature to be stealthy to the immune response of the living organism.     

Bipolar Electrochemical Synthesis of WS2 Nanoparticles and Their Application in Magneto‐Immunosandwich Assay

WS₂ nanoparticles are prepared using bipolar electrochemistry. Obtained material exhibits high activity for hydrogen evolution reaction (HER) and it is used as a label in standard magneto‐immunosandwich assay for protein detection through HER. This new system shows high analytical performance in terms of a wide range, selectivity, sensitivity, and reproducibility.     

Metal Boride‐Based Catalysts for Electrochemical Water‐Splitting: A Review

Electrocatalytic water‐splitting has gained a firm hold in the area of renewable hydrogen production owing to its integrative compatibility with intermittent energy sources. However, wide‐scale implementation of this technology demands discovery of new electrode materials that strike a good balance between efficiency, stability, and cost. In the pool of inexpensive electrodes capable of catalyzing hydrogen and oxygen evolution reactions, metal borides/borates have made a big splash in the last decade. However, the research in this family of electrocatalysts remains unorganized owing to the diversity of reports. This review summarizes the past and present research progress in metal borides/borates for electrocatalytic water‐splitting. The fundamental reasons for electrochemical behavior in different metal borides/borates are highlighted here, also including some comments regarding erroneous practices in the performance evaluation of metal borides/borates. Various strategies used to enhance the electrocatalytic performance of metal borides/borates are discussed in detail. Different methods evolved over the years for the synthesis of metal borides/borates are also discussed. Finally, an assessment of the commercial viability of metal borides/borates is made and future research directions are suggested.     

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

The development of cost‐effective and high‐performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non‐noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high‐spin Co³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate‐spin Co⁴⁺ sites) in RBaCo₂O_5.5+δ (δ = 1/4; R = lanthanides) can produce a near‐ideal HER reaction path to adsorb H₂O and release H₂, respectively. Experimentally, the as‐synthesized (Gd_0.5La_0.5)BaCo₂O_5.75 outperforms the state‐of‐the‐art Pt/C catalyst in many aspects. The proof‐of‐concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near‐optimal synergistic catalytic effect, which is pivotal for rational design of oxygen‐containing materials.     

Self‐Templated Fabrication of CoO–MoO2 Nanocages for Enhanced Oxygen Evolution

Oxygen evolution reaction (OER) plays a key role in energy conversion and storage processes such as water splitting and carbon dioxide reduction. However, the sluggish kinetics caused by insufficient active surface and limited charge transfer hinder OER's wide applications. In this work, a novel self‐templating strategy for the fabrication of composite CoO–MoO₂ nanocages with enhanced OER performance is proposed. By designing a nanocage structure and incorporating conductive MoO₂ to promote both mass and charge transfer, high OER activity (η = 312 mV at 10 mA cm^?2) as well as good stability in the resulting CoO–MoO₂ composite nanostructure can be achieved. This versatile synthetic strategy can also be extended to other metals (such as W) to provide greater opportunities for the controlled fabrication of mixed metal oxide nanostructures for electrochemical applications.     

Under‐Water Superaerophobic Pine‐Shaped Pt Nanoarray Electrode for Ultrahigh‐Performance Hydrogen Evolution

A pine‐shaped Pt nanostructured electrode with under‐water superaerophobicity for ultrahigh and steady hydrogen evolution reaction (HER) performance is successfully fabricated by a facile and easily scalable electrodeposition technique. Due to the lower bubble adhesive force (11.5 ± 1.2 μN), the higher bubble contact angle (161.3° ± 3.4°) in aqueous solution, and the smaller size of bubbles release for pine‐shaped Pt nanostructured electrode, the incomparable under‐water superaerophobicity for final repellence of bubbles from submerged surface with ease, is successfully achieved, compared to that for nanosphere electrode and for Pt flat electrode. With the merits of superior under‐water superaerophobicity and excellent nanoarray morphology, pine‐shaped Pt nanostructured electrode with the ultrahigh electrocatalytic HER performance, excellent durability, no obvious current fluctuation, and dramatically fast current density increase at overpotential range (3.85 mA mV^?1, 2.55 and 13.75 times higher than that for nanosphere electrode and for Pt flat electrode, respectively), is obtained, much superior to Pt nanosphere and flat electrodes. The successful introduction of under‐water superaerophobicity to in‐time repel as‐formed H₂ bubbles may open up a new pathway for designing more efficient electrocatalysts with potentially practical utilization in the near future.     

Superaerophobic Electrode with Metal@Metal‐Oxide Powder Catalyst for Oxygen Evolution Reaction

A stable and highly active oxygen evolution reaction (OER) electrode is the key for fast and robust O₂ production, which is one of the essential points for various kinds of energy conversion systems, such as water splitting, lithium‐O₂ battery and artificial photosynthesis. Here, superaerophobic electrodes with metal@metal‐oxide powder catalysts are shown, which demonstrate high and stable OER activity. The active‐site‐density of metal@metal‐oxide catalysts is increased over one order of magnitude than those of pure metal oxides due to the large enhancement of electrical conductivity, revealing the substantial enhancement of electrochemical OER kinetics. Furthermore, the superaerophobic property of electrodes is favorable for fast O₂ desorption, which improves electrochemical active surface area (EASA) during OER. The superaerophobic electrode with metal@metal‐oxide powder catalysts provides the new insight for increase of active‐site‐density and EASA simultaneously, which are the key factors to determine the activity of OER electrode.     

Emerging Dual‐Channel Transition‐Metal‐Oxide Quasiaerogels by Self‐Embedded Templating

The lack of precise control of particle sizes is the critical challenge in the assembly of 3D interconnected transition‐metal oxide (TMO) for newly‐emerging energy conversion devices. A self‐embedded templating strategy for preparing the TMO@carbon quasiaerogels (TMO@C‐QAs) is proposed. By mimicking an aerogel structure at a microscale, the TMO@C‐QA successfully assembles size‐controllable TMO nanoparticles into 3D interconnected structure with surface‐enriched carbon species. The morphological evolutions of intermediates verify that the self‐embedded Ostwald ripening templating approach is responsible for the dual‐channel TMO@C‐QA formation. The general self‐embedded templating strategy is easily extended to prepare various TMO@C‐QAs, including the Co₃O₄@C‐QA, Mn₃O₄@C‐QA, Fe₂O₃@C‐QA, and NiO@C‐QA. Benefiting from the unparalleled 3D interconnected network of aerogels, the Co₃O₄@C‐QA displays superior bifunctional catalytic activities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as well as high specific capacity and excellent long‐term stability for lithium‐ion battery (LIB) anode. A proof‐of‐concept battery‐powered electrolyzer with Co₃O₄@C‐QA cathode and anode powered by a full LIB with Co₃O₄@C‐QA anode is presented. The battery‐powered electrolyzer made of the state‐of‐the‐art TMOs can exhibit great competitive advantages due to its supreme multifunctional energy conversion performance for future water electrolysis.     

Metal‐Organic Precursor–Derived Mesoporous Carbon Spheres with Homogeneously Distributed Molybdenum Carbide/Nitride Nanoparticles for Efficient Hydrogen Evolution in Alkaline Media

The generation of hydrogen through water electrolysis is considered as a sustainable approach for future fuel production. Molybdenum (Mo)‐based compounds are reported as highly active and inexpensive alternatives to platinum‐based electrocatalysts for the hydrogen evolution reaction (HER). Currently, the major challenge for Mo‐based HER electrocatalysts lies in establishing new concepts of micro‐/nanostructure design to enhance the hydrogen evolution kinetics and realizing facile, large‐scale, and green fabrication processes. Here, a fast, scalable, and eco‐friendly metal‐organic coordination precursor–assisted strategy is reported for synthesizing novel hierarchically mesoporous Mo‐based carbon electrocatalysts for efficient hydrogen production. Benefiting from homogeneously distributed Mo‐based nanocrystallites/heterojunctions and uniform mesopores, the Mo‐based mesoporous electrocatalyst shows high hydrogen evolution activity and stability with a low overpotential of 222 mV at 100 mA cm^?2 (Pt/C: 263 mV), ranging among the best non‐noble metal HER catalysts in alkaline condition. Overall, the discovery of using dopamine–molybdate coordination precursor with silica nanoparticles will not only create a new pathway for controllable synthesis of diverse kinds of micro‐/nanostructured Mo‐based catalysts, but also take a step toward the fast and scale‐up production of advanced mesoporous carbon electrodes for a broad range of applications.     

Protein Fragment Reconstitution as a Driving Force for Self‐Assembling Reversible Protein Hydrogels

Due to their potential biomedical applications, protein‐based hydrogels have attracted considerable interest. Although various methods have been developed to engineer self‐assembling, physically‐crosslinked protein hydrogels, exploring novel driving forces to engineer such hydrogels remains challenging. Protein fragment reconstitution, also known as fragment complementation, is a self‐assembling mechanism by which protein fragments can reconstitute the folded conformation of the native protein when split into two halves. Although it has been used in biophysical studies and bioassays, fragment reconstitution has not been explored for hydrogel construction. Using a small protein GL5 as a model, which is capable of fragment reconstitution to reconstitute the folded GL5 spontaneously when split into two halves, GN and GC, we demonstrate that protein fragment reconstitution is a novel driving force for engineering self‐assembling reversible protein hydrogels. Fragment reconstitution between GN and GC crosslinks GN and GC‐containing proteins into self‐assembling reversible protein hydrogels. These novel hydrogels show temperature‐dependent reversible sol‐gel transition, and excellent property against erosion in water. Since many proteins can undergo fragment reconstitution, we anticipate that such fragment reconstitution may offer a general driving force for engineering protein hydrogels from a variety of proteins, and thus significantly expanding the ‘toolbox’ currently available in the field of biomaterials.     

Hierarchical Graphene‐Based Films with Dynamic Self‐Stiffening for Biomimetic Artificial Muscle

Biological tissues such as muscle cells can adapt their structural and mechanical response upon external mechanical stimuli. Conversely, artificial muscles, intended to reproduce the salient functional features of biological muscles, usually undergo mechanical fatigue when subjected to dynamic stress. Besides passively improving the resilience to dynamic loads, here, it is reported that macroscopic films based on graphene and its chemical derivate exhibit an increase in modulus by up to 84% after subjected to a low‐amplitude (0.1%) dynamic tension. Through a combination of experimental testing and molecular dynamics simulations, the unique self‐stiffening behavior is attributed to the straightening and reorientation of graphene sheets and is further tuned through tailoring interlayer adhesion. Meanwhile, artificial muscles based on graphene films are designed and interestingly improved stiffness of our muscle materials after “training” are demonstrated. These results help to harness the stiffening mechanism and can be useful for the development of adaptable structural materials for biomechanical applications.     

An Inkjet‐Printed Field‐Effect Transistor for Label‐Free Biosensing

A flexible, biological field‐effect transistor (BioFET) for use in biosensing is reported. The BioFET is based on an organic thin‐film transistor (OTFT) fabricated mainly by inkjet printing and subsequently functionalized with antibodies for protein recognition. The BioFET is assessed for label‐free detection of a model protein, human immunoglobulin G (HIgG). It is characterized electrically to evaluate the contribution of each step in the functionalization of the OTFT and to detect the presence of the target protein. The fabrication, structure, materials optimization, electrical characteristics, and functionality of the starting OTFT and final BioFET are also discussed. Different materials are evaluated for the top insulator layer, with the aim of protecting the lower layers from the electrolyte and preserving the BioFET electrical performance.     

Localized Laser‐Based Photohydrothermal Synthesis of Functionalized Metal‐Oxides

We discuss the rapid in situ hydrothermal synthesis of metal oxide materials based on the photothermal superheating of light‐absorbing metal layers for simple and facile on‐demand placement of semiconductor materials with micrometer‐scale lateral resolution. Localized heating from pulsed and focused laser illumination enables ultrafast growth of metal oxide materials with high spatiotemporal precision in aqueous precursor solution. Among many possible electronic and optoelectronic applications, the proposed method can be used for laser‐based in situ real‐time soldering of separated metal structures and electrodes with functionalized semiconductor materials. Resistive electrical interconnections of metal strip lines as well as sensitive UV detection using photohydrothermally grown metal oxide bumps are experimentally demonstrated.     

Protein Particles Formed by Protein Activation and Spontaneous Self‐Assembly

In this article, a non‐chemical crosslinking method is used to produce pure protein microparticles with an innovative approach, so‐called protein activation spontaneous and self‐assembly (PASS). The fabrication of protein microparticles is based on the idea of using the internal disulfide bridges within protein molecules as molecular linkers to assemble protein molecules into a microparticle form. The assembly process is triggered by an activating reagent–dithiothreitol (DTT), which only involved in the intermediate step without being incorporated into the resulting protein microparticles. Conventional protein microparticle fabrication methods usually involve emulsification process and chemical crosslink reactions using amine reactive reagents such as glutaraldehdye or EDC/NHS. The resulting protein microparticles are usually having various size distributions. Most importantly crosslinking reactions using amine reactive reagents will result in producing protein microparticles with undesired properties such as auto‐fluorescence and high toxicity. In contrast to the conventional methods, our technology provides a simple and robust method to produce highly homogeneous, stable and non‐fluorescence pure protein microparticles under mild conditions at physiological pH and temperature. The protein microparticles are found to be biodegradable, non‐toxic to MDCK cells and with preserved biological activities. Results on the cytotoxcity study and enzyme function demonstrate the potential applications of the protein microparticles in the area of pharmaceutics and analytical chemistry.     

Quantum‐Dot‐Tagged Bioresponsive Hydrogel Suspension Array for Multiplex Label‐Free DNA Detection

A novel hydrogel suspension array, which possesses the joint advantages of quantum‐dot‐encoded technology, bioresponsive hydrogels, and photonic crystal sensors with full multiplexing label‐free DNA detection capability is developed. The microcarriers of the suspension array are quantum‐dot‐tagged DNA‐responsive hydrogel photonic beads. In the case of label‐free DNA detection, specific hybridization of target DNA and the crosslinked single‐stranded DNA in the hydrogel grid will cause hydrogel shrinking, which can be detected as a corresponding blue shift in the Bragg diffraction peak position of the beads that can be used for quantitatively estimating the amount of target DNA. The results of the label‐free DNA detection show that the suspension array has high selectivity and sensitivity with a detection limit of 10^?9 M . This method has the potential to provide low cost, miniaturization, and simple and real‐time monitoring of hybridization reaction platforms for detecting genetic variations and sequencing genes.