Metallic Heterostructures for Plasmon-Enhanced Electrocatalysis.

Metallic heterogeneous nanostructures with plasmonic functionality have attracted great attention in the field of plasmon-enhanced electrocatalysis, where surface plasmons produced under light excitation could facilitate the overall electrocatalytic performances. Owing to their controllability, multifunctionality, and complexity, heterogeneous metallic nanostructures take advantages of the properties from individual components and synergistic effects from adjacent components, thus may achieve remarkable electrocatalytic performances. This review highlights the state-of-the-art progress of the application of metallic heterostructures for plasmon-enhanced electrocatalysis. First, a brief introduction to plasmonic heterogeneous nanostructures is demonstrated. Then, fundamental principles of localized surface plasmon resonance and the underlying mechanisms of plasmonic heterogeneous nanostructures in catalysis are discussed. This is followed by a discussion of recent advances of plasmonic heterogeneous nanostructures in plasmon-enhanced electrocatalysis, in which the enhanced activity, selectivity, and stability are particularly emphasized. Finally, an outlook of remaining challenges and future opportunities for plasmonic heterogeneous nanomaterials and plasmon-related electrocatalysis is presented.

Engineering the Metal/Oxide Interface of Pd Nanowire@CuOx Electrocatalysts for Efficient Alcohol Oxidation Reaction.

The development of new type electrocatalysts with promising activity and antipoisoning ability is of great importance for electrocatalysis on alcohol oxidation. In this work, Pd nanowire (PdNW)/CuOx heterogeneous catalysts with different types of PdOCu interfaces (Pd/amorphous or crystalline CuOx ) are prepared via a two-step hydrothermal strategy followed by an air plasma treatment. Their interface-dependent performance on methanol and ethanol oxidation reaction (MOR and EOR) is clearly observed. The as-prepared PdNW/crystalline CuOx catalyst with 17.2 at% of Cu on the PdNW surface exhibits better MOR and EOR activity and stability, compared with that of PdNW/amorphous CuOx and pristine PdNW catalysts. Significantly, both the cycling tests and the chronoamperometric measurements reveal that the PdNW/crystalline CuOx catalyst yields excellent tolerance toward the possible intermediates including formaldehyde, formic acid, potassium carbonate, and carbon monoxide generated during the MOR process. The detailed analysis of their chemical state reveals that the enhanced activity and antipoison ability of the PdNW/crystalline CuOx catalyst originates from the electron-deficient Pdδ+ active sites which gradually turn into Pd5 O4 species during the MOR catalysis. The Pd5 O4 species can likely be stabilized by moderate crystalline CuOx decorated on the surface of PdNW due to the strong PdOCu interaction.

A Separation-Sensing Membrane Performing Precise Real-Time Serum Analysis During Blood Drawing.

Dynamic and on-site analysis of serum from human blood is crucial, however, state-of-the-art blood-assay methods can only collect single or discrete data of physiological analytes; thus, the online reports of the dynamic fluctuation of key analytes remains a great challenge. Here, we propose a novel separation-sensing membrane by constructing a heterogeneous-nanostructured architecture, wherein a surface nanoporous layer continuously extracts serum, while the biosensing nanochannels underneath dynamically recognise biotargets, thereby achieving a continuous testing of vital clinical indices as blood is drawn. By precisely controlling the pore structure and nanoshape of biosensing crystals, this membrane achieved accurate and online glucose and lactate monitoring in patients with a variety of medical conditions within 1 min, which is one order of magnitude faster than state-of-the-art techniques. Moreover, various kinds of bio-recognisers can be introduced into this membrane to accurately detect glutamate, transaminase, and cancer biomarkers.

Self-Assembly of Heterogeneous Ferritin Nanocages for Tumor Uptake and Penetration.

Well-defined nanostructures are crucial for precisely understanding nano-bio interactions. However, nanoparticles (NPs) fabricated through conventional synthesis approaches often lack poor controllability and reproducibility. Herein, a synthetic biology-based strategy is introduced to fabricate uniformly reproducible protein-based NPs, achieving precise control over heterogeneous components of the NPs. Specifically, a ferritin assembly toolbox system is developed that enables intracellular assembly of ferritin subunits/variants in Escherichia coli. Using this strategy, a proof-of-concept study is provided to explore the interplay between ligand density of NPs and their tumor targets/penetration. Various ferritin hybrid nanocages (FHn) containing human ferritin heavy chains (FH) and light chains are accurately assembled, leveraging their intrinsic binding with tumor cells and prolonged circulation time in blood, respectively. Further studies reveal that tumor cell uptake is FH density-dependent through active binding with transferrin receptor 1, whereas in vivo tumor accumulation and tissue penetration are found to be correlated to heterogeneous assembly of FHn and vascular permeability of tumors. Densities of 3.7 FH/100 nm2 on the nanoparticle surface exhibit the highest degree of tumor accumulation and penetration, particularly in tumors with high permeability compared to those with low permeability. This study underscores the significance of nanoparticle heterogeneity in determining particle fate in biological systems.

Element specific atom counting for heterogeneous nanostructures: Combining multiple ADF STEM images for simultaneous thickness and composition determination.

In this paper, a methodology is presented to count the number of atoms in heterogeneous nanoparticles based on the combination of multiple annular dark field scanning transmission electron microscopy (ADF STEM) images. The different non-overlapping annular detector collection regions are selected based on the principles of optimal statistical experiment design for the atom-counting problem. To count the number of atoms, the total intensities of scattered electrons for each atomic column, the so-called scattering cross-sections, are simultaneously compared with simulated library values for the different detector regions by minimising the squared differences. The performance of the method is evaluated for simulated Ni@Pt and Au@Ag core-shell nanoparticles. Our approach turns out to be a dose efficient alternative for the investigation of beam-sensitive heterogeneous materials as compared to the combination of ADF STEM and energy dispersive X-ray spectroscopy.

Optimal experiment design for element specific atom counting using multiple annular dark field scanning transmission electron microscopy detectors.

This paper investigates the possible benefits for counting atoms of different chemical nature when analysing multiple 2D scanning transmission electron microscopy (STEM) images resulting from independent annular dark field (ADF) detector regimes. To reach this goal, the principles of statistical detection theory are used to quantify the probability of error when determining the number of atoms in atomic columns consisting of multiple types of elements. In order to apply this theory, atom-counting is formulated as a statistical hypothesis test, where each hypothesis corresponds to a specific number of atoms of each atom type in an atomic column. The probability of error, which is limited by the unavoidable presence of electron counting noise, can then be computed from scattering-cross sections extracted from multiple ADF STEM images. Minimisation of the probability of error as a function of the inner and outer angles of a specified number of independent ADF collection regimes results in optimal experimental designs. Based on simulations of spherical Au@Ag and Au@Pt core-shell nanoparticles, we investigate how the combination of two non-overlapping detector regimes helps to improve the probability of error when unscrambling two types of atoms. In particular, the combination of a narrow low angle ADF detector with a detector formed by the remaining annular collection regime is found to be optimal. The benefit is more significant if the atomic number Z difference becomes larger. In addition, we show the benefit of subdividing the detector regime into three collection areas for heterogeneous nanostructures based on a structure consisting of three types of elements, e.g., a mixture of Au, Ag and Al atoms. Finally, these results are compared with the probability of error resulting when one would ultimately use a pixelated 4D STEM detector and how this could help to further reduce the incident electron dose.

Shape-Controlled and Well-Arrayed Heterogeneous Nanostructures via Melting Point Modulation at the Nanoscale.

A novel method for fabricating shape-controlled and well-arrayed heterogeneous nanostructures by altering the melting point of the metal thin film at the nanoscale is proposed. Silver nanofilms (AgNFs) are transformed into silver nanoislands (AgNIs), silver nanoparticles (AgNPs), and silver nanogaps (AgNGs) that are well-ordered and repositioned inside the gold nanoholes (AuNHs) depending on the diameter of the AuNHs, the thickness of the AgNF, and the heating temperature (120-200 °C). This method demonstrates the ability to fabricate uniform, stable, and unique structures with a fast, simple, and mass-producible process. For demonstrating the diverse applicability of the developed structures, high-density AgNGs inside the AuNHs are utilized as surface-enhanced Raman spectroscopy (SERS) substrates. These AgNGs-based SERS substrates exhibit a performance enhancement, which is 1.06 × 106 times greater than that of a metal film, with a relative standard deviation of 19.8%. The developed AgNP/AgNI structures are also used as nonreproducible anti-counterfeiting signs, and the anti-counterfeiting/readout system is demonstrated via image processing. Therefore, our method could play a vital role in the nanofabrication of high-demand nanostructures.

DNA-Based Plasmonic Heterogeneous Nanostructures: Building, Optical Responses, and Bioapplications.

The integration of multiple functional nanoparticles into a specific architecture allows the precise manipulation of light for coherent electron oscillations. Plasmonic metals-based heterogeneous nanostructures are fabricated by using DNA as templates. This comprehensive review provides an overview of the controllable synthesis and self-assembly of heterogeneous nanostructures, and analyzes the effects of structural parameters on the regulation of optical responses. The potential applications and challenges of heterogeneous nanostructures in the fields of biosensors and bioanalysis, in vivo monitoring, and phototheranostics are discussed.

Heterogeneous Nanostructures Fabricated via Binding Energy-Controlled Nanowelding.

A novel concept for fabricating heterogeneous nanostructures based on different melting temperatures is developed. Au-Ag composite cross-structures are fabricated by nanowelding technologies. During the fabrication of Au-Ag composite cross-structures, Ag nanowires transform into ordered particles decorating the Au nanowire surfaces with an increase in the welding temperature because of the different melting temperatures of Au and Ag. To compare and explain the melting temperatures, the thicknesses of Au and Ag nanowires as parameters are analyzed. Scanning electron microscopy and focused ion beam imaging are used to observe the morphologies and cross sections of the fabricated samples. The evolution of 3D nanostructures is observed by atomic force microscopy, whereas the compositions and binding energies of the nanostructures are determined by X-ray diffraction and X-ray photoelectron spectroscopies. In addition, the atomic structures are analyzed by transmission electron microscopy, and the optical properties of the fabricated nanostructures are evaluated by spectrometry. Furthermore, color filter electrodes are fabricated, and their polarization properties are evaluated by sheet resistance measurements and observing the color and brightness of light-emitting diodes. The proposed method is suitable for application in various fields such as biosensors, optics, and medicine.