Lifeng Hang

A functional hydrogel film attached with a 2D Au nanosphere array and its ultrahigh optical diffraction intensity as a visualized sensor

Free-standing 2D Au nanosphere array/hydrogel composite sensing films were prepared by attaching a 2D Au nanosphere array onto a polyacrylic acid (PAAc) hydrogel film, which could be used as visualized sensors. These 2D Au nanosphere array/hydrogel composite films displayed visually diffraction color and much stronger diffraction intensity due to their periodic structures and large scattering cross-section of the Au nanospheres. Their diffraction intensity was increased by more than one order of magnitude (88 times) compared to that of 2D PS sphere array/hydrogel composite films to external stimuli, which is useful for visual observation by the naked eye and further optical characterization. Such 2D Au nanosphere array/hydrogel composite films exhibit ultrahigh diffraction intensity for them to be used for the visual determination of an analyte. The presented strategy could be extended to develop different visualized sensors based on various functional hydrogel films.

Optical sensor based on hydrogel films with 2D colloidal arrays attached on both the surfaces: anti-curling performance and enhanced optical diffraction intensity

An interesting strategy to create free standing hydrogel composite films with colloidal monolayers attached on both the surfaces, which could act as visualizing sensors with high diffraction intensity, is developed. Owing to the balanced stress on both the surfaces, the colloidal monolayer–hydrogel composite films overcome the curling problem of traditional hydrogel films loaded with a colloidal monolayer on one side. They also display enhanced diffraction intensity compared to those with the attachment of only a single 2D colloidal monolayer due to a multi-diffraction effect. Such sensing hydrogel composite films with anti-curling performance and enhanced optical diffraction intensity are very helpful to improve their practical applications in visual and quantitative detection. In addition, this strategy is universal and could be suitable for fabricating various functional hydrogel films loaded with different nanosphere arrays for novel optical sensors.

Aligned gold nanobowl arrays: their fabrication, anisotropic optical response and optical grating applications

A simple, low-cost and high-throughput technique to fabricate aligned Au nanobowl arrays is presented by combining template-assisted self-assembly and colloidal lithography. Polystyrene (PS) colloids were self-assembled into the aligned grooves on a blank digital versatile disc (DVD) substrate, forming aligned PS colloidal necklace arrays. After being coated with an Au layer, they were inverted onto another glass slide with a polyvinyl alcohol (PVA) thin layer and aligned Au nanobowl arrays were obtained after peeling off the DVD substrate and removing the PS colloidal spheres. If the glass slide substrate was removed, the aligned Au nanobowl arrays on a flexible PVA substrate could be achieved. These Au nanobowl alignments displayed higher reflectance and could be used as an optical grating. They also demonstrated anisotropic optical properties and have important potential applications in optical devices, such as optical gratings, waveguide, and so on. This work will provide new insights and understanding of the control of morphology and enhancement of optical properties of Au nanoparticle arrays and it is helpful to develop new optical devices based on such anisotropic optical performance.

Hierarchical micro/nanostructured C doped Co/Co3O4 hollow spheres derived from PS@Co(OH)2 for the oxygen evolution reaction

Hierarchical micro/nanostructured C doped Co/Co3O4 hollow spheres were prepared by two-step treatment (annealing at 600 °C in an Ar atmosphere and then at 250 °C in air) of PS@Co(OH)2 core–shell structures templated from PS microspheres without any modification. In 1 M KOH, such hollow nanospheres showed an overpotential of 352 mV at a benchmark oxygen evolution reaction (OER) current density of 10 mA cm−2, which was lower than that of RuO2 (364 mV), Co3O4 hollow nanospheres (410 mV) and C-Co/Co3O4 nanoparticles (462 mV). Importantly, the C-Co/Co3O4 hollow spheres exhibited a small onset potential (1.49 V) due to their more active sites, higher electrical conductivity, larger specific surface area, and excellent electron and ion diffusion permeability. This work provides a strategy to design and fabricate earth-abundant, low-cost electrocatalysts for water splitting in practical applications.

Periodic nanostructured Au arrays on an Si electrode for high-performance electrochemical detection of hydrogen peroxide without an enzyme

Periodic gold nanosphere arrays were prepared on a planar silicon substrate, which could be directly developed as an electrode to sensitively and selectively detect H2O2 without an enzyme via an electrochemical method. The arrays of Au nanospheres were fabricated on a large scale (∼cm2) on the Si substrate using polystyrene (PS) colloidal monolayers as the template, after Au deposition and subsequent annealing. The developed biosensor based on the Au nanosphere arrays on the Si substrate demonstrated excellent catalytic activity towards H2O2 over a wide linear range of 0.2 μM–5 mM with a very low detection limit of 0.1 μM. Importantly, the electrochemical biosensor possessed good stability and high reproducibility. The catalytic activity can be enhanced by reducing the gold nanoparticle size and periodic length in the array. The biosensors based on periodic Au nanosphere arrays used to determine the concentration of H2O2 have the advantages of non-enzymatic detection and non-Pt electrode strategy when compared to the conventional method, which may open up new horizons in the production of outstanding biosensors and can be used as a platform for the preparation of various electrochemical biosensors.

Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks

A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10(-10) M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

Functionalized periodic Au@MOFs nanoparticle arrays as biosensors for dual-channel detection through the complementary effect of SPR and diffraction peaks

A facile and low-cost method to prepare periodic Au@metal–organic framework (MOF) (MIL-100(Fe)) nanoparticle arrays was developed. The arrays were fabricated in situ using monolayer colloidal crystals as templates, followed by Au deposition on substrates, and annealing. MIL-100(Fe) coatings were applied on the nanospheres using a simple solvent thermal process. The prepared periodic Au@MIL-100(Fe) nanoparticle (NP) arrays were characterized by two peaks in the visible spectra. The first peak represented the surface plasmon resonance (SPR) of the Au nanospheres, and the other peak, or the diffraction peak, originated from the periodic structure in the NP array. After modification with 3-aminophenylboronic acid hemisulfate (PBA), the Au@MIL-100(Fe) NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity. These responses could be due to the strong interaction between PBA and glucose molecules. The diffraction peak was sensitive at low glucose concentrations (less than 12 mM), whereas the SPR peak rapidly responded at high concentrations. The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions. These results can be used to develop a dual-channel biosensor. We also created a standard diagram, which can be used to efficiently monitor blood glucose levels. The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100(Fe) NP arrays functionalized with different recognition agents.

A novel process to prepare a thin silica shell on the PDDA-stabilized spherical Au nanoparticles assisted by UV light irradiation

A modified polyol process is a convenient route to prepare monodispersed, uniform spherical Au nanospheres stabilized by Poly Diallyl Dimethyl Ammonium Chloride (PDDA). However, Au nanospheres with PDDA coatings possess a high zeta potential and such PDDA coatings can not be removed easily, leading to a difficulty in coating a silica layer on surfaces of Au nanospheres, further resulting in the limitation of the applications of these monodispersed Au nanoparticles (NPs). Herein, we develop a novel route to coat a silica layer on PDDA stabilized Au nanospheres assisted by UV light irradiation without the use of a silane coupling agent as the surface primer. PDDA-stabilized Au nanospheres showed high a positive zeta potential (36.7 mV), which is disadvantageous to coat a layer of thin silica shell. In our strategy, UV light irradiation with high power was applied to PDDA stabilized Au nanoparticles and part of PDDA on Au nanoparticles was degradated, producing lower positive zeta potential (14.7 mV), which guaranteed that silica shell could be easily formed on the surface of Au sphere under such a low zeta potential. The thickness of silica shell could be successfully tuned from 2 nm to 8 nm by adjusting the concentration of TEOS. As far as we know, this is first report to coat the silica layer on PDDA stabilized Au nanospheres. Such monodispersed Au spherical nanoparticles with controlled silica coatings could be extended to important applications in SERS applications, electrochemistry after self-assembled into monolayer particle arrays.

Controlled synthesis of sponge-like porous Au–Ag alloy nanocubes for surface-enhanced Raman scattering properties

We develop an interesting route to prepare new sponge-like Au–Ag alloy nanocubes (NCs) with controlled porosity and atomic percentage through an interparticle alloying and dealloying process. Au@Ag NCs were first synthesized using Au nanooctahedra as initial seeds. Then, the Au@Ag NCs were covered with SiO2 and thermally annealed, forming solid Au–Ag alloy NCs with a SiO2 layer. After removing the majority of the SiO2 layer and leaching less-stable Ag from solid Au–Ag alloy NCs, uniform sponge-like porous Au–Ag alloy NCs were obtained. In this process, SiO2 not only prevents fusion between adjacent Au@Ag NPs under thermal annealing, but also directs the final shape of sponge-like Au–Ag alloy NPs with a cubic shape as a template. Thanks to the high-density “hotspots” in nanopores, sharp corners and edges, and a synergistic effect between Au and Ag species, such sponge-like Au–Ag alloy NCs showed excellent SERS performance with an enhancement factor of ∼108, which can effectively detect 4-aminothiophenol (4-ATP) at a concentration as low as 1 × 10−10 M. This strategy is universal and it can be extended to prepare sponge-like Au–Ag alloy NPs with different accurate shapes. Such sponge-like nanoporous alloy NPs have many potential applications such as in plasmonics, SERS, drug delivery, photothermal therapy, and catalysis systems.

Rapid and Efficient Self-Assembly of Au@ZnO Core–Shell Nanoparticle Arrays with an Enhanced and Tunable Plasmonic Absorption for Photoelectrochemical Hydrogen Generation

High-quality Au@ZnO core-shell nanoparticle (NP) array films were easily and efficiently fabricated through an air/water interfacial self-assembly. These materials have remarkable visible light absorption capacity and fascinating performance in photoelectrochemical (PEC) water splitting with a photocurrent density of ∼3.08 mA/cm2 at 0.4 V, which is superior to most ZnO-based photoelectrodes in studies. Additionally, the interesting PEC performance could be effectively adjusted by altering the thickness of the ZnO shell and/or the layer number of the array films. Results indicated that the bilayer film based on Au@ZnO NPs with 25 nm shell thickness displayed optimal behavior. The remarkable PEC capability could be ascribed to the enhanced light-harvesting ability of the Au@ZnO structured NPs by the SPR effect and the optimum film thickness. This work demonstrates a desirable paradigm for preparing photoelectrodes based on the synergistic effect of plasmatic NPs as the core and a visible optical absorbent and semiconductor as the shell. Moreover, this work provides a new approach for fabricating optoelectronic anode thin film devices through a self-assembly method.