Huilin Li

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.

Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly Sensitive SERS Performance with Good Reproducibility and High Density of Hotspots

Periodic porous alloyed Au-Ag nanosphere (NS) arrays with different periodic lengths and tunable composition ratios were prepared on Si substrates on a large scale (∼cm2) using stepwise metal deposition-annealing and subsequent chemical corrosion from a monolayer of colloidal polystyrene (PS) microspheres as the initial template. The porous alloyed Au-Ag NSs possessed a high porosity and bicontinuous morphology composed of hierarchically interconnected ligaments, which were obtained from an optimized dealloying process in nitric acid. Interestingly, when the dealloying time was prolonged, the average size of the porous alloyed NSs slightly decreased, and the width of the ligaments gradually increased. The periodic length of the array could be facilely changed by controlling the initial particle size of the PS template. Moreover, the porous alloyed Au-Ag NS arrays were explored as a platform for the surface-enhanced Raman scattering (SERS) detection of 4-aminothiophenol (4-ATP) and exhibited excellent reproducibility and high sensitivity because of the periodic structure of the arrays and the abundance of inherent hotspots. After optimization experiments, a low concentration of 10-10 M 4-ATP could be detected on these porous Au-Ag NS array substrates. Such highly reproducible SERS activity is meaningful for improving the practical application of portable Raman detection equipment.

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.

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.

Strong Electronic Interaction in Dual-Cation-Incorporated NiSe2 Nanosheets with Lattice Distortion for Highly Efficient Overall Water Splitting

Exploring highly efficient and low-cost electrocatalysts for electrochemical water splitting is of importance for the conversion of intermediate energy. Herein, the synthesis of dual-cation (Fe, Co)-incorporated NiSe2 nanosheets (Fe, Co-NiSe2 ) and systematical investigation of their electrocatalytic performance for water splitting as a function of the composition are reported. The dual-cation incorporation can distort the lattice and induce stronger electronic interaction, leading to increased active site exposure and optimized adsorption energy of reaction intermediates compared to single-cation-doped or pure NiSe2 . As a result, the obtained Fe0.09 Co0.13 -NiSe2 porous nanosheet electrode shows an optimized catalytic activity with a low overpotential of 251 mV for oxygen evolution reaction and 92 mV for hydrogen evolution reaction (both at 10 mA cm-2 in 1 m KOH). When used as bifunctional electrodes for overall water splitting, the current density of 10 mA cm-2 is achieved at a low cell voltage of 1.52 V. This work highlights the importance of dual-cation doping in enhancing the electrocatalyst performance of transition metal dichalcogenides.

Optical sensing properties of Au nanoparticle/hydrogel composite microbeads using droplet microfluidics

Uniform Au nanoparticle (NP)/poly (acrylamide-co-acrylic acid) [P(AAm-co-AA)] hydrogel microbeads were successfully prepared using droplet microfluidics technology. The microbeads exhibited a good stimuli-responsive behavior to pH value. Particularly in the pH value ranging from pH 2-pH 9, the composite microbead sizes gradually increased along with the increase of pH value. The homogeneous Au NPs, which were encapsulated in the P(AAm-co-AA) hydrogel microbeads, could transform the volume changes of hydrogel into optical signals by a tested single microbead with a microspectrometre system. The glucose was translated into gluconic acid by glucose oxidase. Thus, the Au NP/P(AAm-co-AA) hydrogel microbeads were used for detecting glucose based on pH effects on the composite microbeads. For this, the single Au NP/P(AAm-co-AA) hydrogel microbead could act as a good pH- or glucose-visualizing sensor.

Surface enhanced Raman scattering properties of dynamically tunable nanogaps between Au nanoparticles self-assembled on hydrogel microspheres controlled by pH

We developed an interesting route for preparing a poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogel microsphere with a coating of Au nanospheres (hydrogel microsphere @ Au nanospheres) through self-assembly based on electrostatic interaction. The fabricated composites could be used as highly sensitive enhanced Raman scattering substrates. The nanogaps between adjacent Au nanospheres were dynamically tuned by volume changes in the hydrogel microspheres in the semiwet state under different pH conditions. At pH 6, the hydrogel microsphere @ Au nanospheres demonstrated highly sensitive SERS with an enhancement factor of 109. The product could detect very low concentrations of analytes up to 10-12M 4-aminothiophenol (4-ATP) molecules. This paper proposes a new method for detecting trace amounts of environmental organic pollutants by dynamically tuning the SERS enhancement in the semiwet testing state.

Physical process-aided fabrication of periodic Au–M (M = Ag, Cu, Ag–Cu) alloyed nanoparticle arrays with tunable localized surface plasmon resonance and diffraction peaks

Periodic alloyed (Au–Ag, Au–Cu, Au–Ag–Cu) nanoparticle (NP) arrays with uniform size, controllable composition and center-to-center spacing were fabricated by a novel and facile strategy based on physical vapor deposition on a monolayer colloidal crystal template and further heat treatment. The composition and center-to-center spacing were manipulated by adjusting the sputtering target in the deposition process and the size of colloidal spheres of the template, respectively. The shadow effect and a dewetting model were employed to analyze the whole process of evolution from a metallic thin film to spherical nanoparticles with uniform size. The localized surface plasmon resonance (LSPR) and diffraction peaks of these alloyed arrays were systematically measured. The dielectric constant has an important influence on LSPR peaks and diffraction peaks. Both the LSPR and diffraction peaks of Au–Ag alloyed NPs arrays exhibit a blue shift due to their lower dielectric constant than that of pure Au NPs. However, compared with Au, Cu possesses a higher dielectric constant, leading to a red shift of the LSPR and diffraction peaks of Au–Cu alloyed NPs arrays. With the increase of NP size, the diffraction peaks of both binary alloyed NPs exhibit a slight red shift. Moreover, the LSPR absorption peaks were more sensitive to the composition of the NPs than the diffraction peaks. This work would open up a novel strategy in the production of alloyed NP arrays with tunable LSPR peaks and diffraction peaks, which would be very helpful to improve their practical applications in various fields.