Ju Xu

Direct electrochemistry of horseradish peroxidase immobilized on a monolayer modified nanowire array electrode

Vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three-dimensional (3D) matrix for immobilization of redox proteins. Third-generation H(2)O(2) biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE(5h) (5h deposition time) exhibited remarkable sensitivity (45.86 microA mM(-1) cm(-2)) towards H(2)O(2) with a detection limit of 0.42 microM (S/N=3), linearity up to 15 mM and a response time of 4s. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.

Silver nanowire array-polymer composite as thermal interface material

Silver nanowire arrays embedded inside polycarbonate templates are investigated as a viable thermal interface material for electronic cooling applications. The composite shows an average thermal diffusivity value of 1.89×10−5 m2 s−1, which resulted in an intrinsic thermal conductivity of 30.3 W m−1 K−1. The nanowires’ protrusion from the film surface enables it to conform to the surface roughness to make a better thermal contact. This resulted in a 61% reduction in thermal impedance when compared with blank polymer. An ∼30 nm Au film on the top of the composite was found to act as a heat spreader, reducing the thermal impedance further by 35%. A contact impedance model was employed to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young’s modulus of the composite is the defining factor in the overall thermal impedance of these composites.

Disposable biosensor based on immobilisation of glutamate oxidase on Pt nanoparticles modified Au nanowire array electrode

Novel electrochemical platform based on Pt nanoparticle modified ordered three-dimensional gold nanowire arrays (PtNP/NAEs) for the amperometric sensing of H(2)O(2) and glutamate is developed. Pt nanoparticle (PtNP) is fabricated by electrodeposition onto the 3D nanowires and characterised using scanning electron microscopy (SEM) and cyclic voltammetry. The deposited nanoparticles have an average size of 20 nm. The PtNP/NAE shows a linear response of up to 20 mM for H(2)O(2) detection with a sensitivity of 194.60 μA mM(-1) cm(-2) at 20°C. It can detect 1 μM (S/N=3) of H(2)O(2) at normal condition without using any enzyme or mediator. Analytical performance of this electrode is tested by immobilising glutamate oxidase (GlutOx) through cross-linking in the matrix of bovine serum albumin (BSA), Nafion and glutaraldehyde. At physiological pH, the biosensor showed the sensitivity of 10.76 μA mM(-1) cm(-2), with a linear range of up to 0.8 mM.

Lu2CaMg2(Si1−xGex)3O12:Ce3+ solid-solution phosphors: bandgap engineering for blue-light activated afterglow applicable to AC-LED

Persistent luminescence (PersL) has long commanded the curiosity of researchers owing to the complicated and profound physics behind it. In this work, the PersL mechanism in a new kind of persistent garnet phosphors, Lu2CaMg2(Si1−xGex)3O12:Ce3+, is studied from the new perspective of a “solid-solution” scheme. Different from the conventional study in pursuit of long PersL, we focus on manipulation of afterglow to the millisecond range and tentatively demonstrate its potential to compensate the flickering of the alternating current driven LED (AC-LED) in every AC cycle. Evidently, the tailored host bandgap favors efficient electron charging and facilitates electron detrapping, as well as redeploying trap distribution, which results in a blue light activated afterglow in the millisecond time range, and subsequently a reduced percent flicker of 64.1% for the AC-LED. This investigation is the first attempt to establish the design guidelines for new PersL materials with an adjustable millisecond ranged afterglow, and, hopefully, it paves a pathway to the development of burgeoning low-flickering AC-LED technology.

Metal nanowire-polymer nanocomposite as thermal interface material

Thermal properties of silver nanowire-silicone (AgNW-silicone) composites at different weight percentage of AgNW in the polymer were studied. The thermal conductivity of these composites was measured using the heat stack method according to D5470 standard. The silver nanowires were synthesized using a polyol process. The nanocomposites were prepared by solution mix processing. The effective thermal conductivity of the AgNW-silicone nanocomposite increased with the enhancement of AgNW concentration and the thermal conductivity were found higher than that of traditional silicone composites using micron sized silver flakes as fillers with the same concentration.

Structure and luminescence behavior of a single-ion activated single-phased Ba2Y3(SiO4)3F:Eu white-light phosphor

The development of a single-ion activated single-phased white-light phosphor is of great importance in the field of near ultraviolet based w-LED lighting. In this work, a Ba2Y3(SiO4)3F:Eu fluoride apatite, which shows a broad emission band covering the entire visible region with tunable color rendition, was successfully synthesized via a high-temperature solid-state route. The microstructure and composition of the phosphor were carefully examined with the aid of XRD Rietveld refinement, HRTEM and SEM analyses, as well as XPS measurement. Spectroscopic studies revealed the site occupancy conditions of Eu2+, i.e., the Eu2+(I) band centering at 470 nm originates from the [BaO9] 4f site, while the Eu2+(II) one peaking at 600 nm comes from the [BaO6F] 6h site. Interestingly, the obtained white light can be readily tuned from cool to warm just by varying the Eu doping content. The brightest luminescence was achieved when the Eu concentration reached 1 mol%, beyond which the d–d interaction-based energy transfer between Eu2+ ions would result in concentration quenching. The underlying mechanism of the incomplete conversion from Eu3+ to Eu2+ under a reducing atmosphere was explored, which was believed to be caused by the rigid framework of the crystal structure. After coupling Ba2Y3(SiO4)3F:Eu with a commercial 3W 370 nm UV chip, the constructed w-LED yielded warm white light with a CIE coordinate of (0.402, 0.371), CCT of 3530 K, and CRI of 83.5, upon being driven by a 350 mA forward-biased current.

Syntheses of complex mesoporous silicas using mixtures of nonionic block copolymer surfactants: understanding formation of different structures using solubility parameters.

The use of block copolymer (BCP) nonionic surfactant mixtures (including Pluronic, Brij and Tetronic types) as templates for synthesizing porous silica materials of mixed pore sizes is explored here. These systems have important applications because combinations of pore sizes can allow rapid access of reactants (via large pores) whilst providing the very high surface area of small pores for higher reaction rates or size selectivity. Examples of the materials prepared here include pore size bimodal hexagonal p6mm channel structures and cubic Im3m cage structures. It is shown here that the chemical similarity, as indicated by the solubility parameter, of the surfactants is an important factor in determining the pore structure and size distribution (PSD) of the pores. Monomodal pore structures are usually obtained when the solubility parameters of the surfactants are similar and bimodal pore structures when the solubility parameters are reasonably different. When the interaction parameter is very high disordered porous systems are formed. Ternary co-surfactant systems, e.g. P123-25R4-P65, can also yield highly ordered bimodal mesoporous silica with a hexagonal structure.

A highly-distorted octahedron with a C2v group symmetry inducing an ultra-intense zero phonon line in Mn4+-activated oxyfluoride Na2WO2F4

Owing to the magnetic dipole nature, the zero phonon line (ZPL) of Mn4+:2E → 4A2 transition is weak unless Mn4+ is situated at a site deviating from the centrosymmetric nature. Herein, we report a brand-new oxyfluoride, Na2WO2F4:Mn4+(NWOF:Mn4+), which shows unprecedented intense red ZPL at ∼620 nm along with relatively weak vibronic transitions under blue light excitation. This peculiar spectral feature is demonstrated to be originated from the highly distorted octahedral coordination environment in the C2v group symmetry surrounding Mn4+. High-resolution spectroscopic studies at 10 K disclose the fine structured electronic/vibronic transitions of Mn4+:2E, 2T1 → 4A2 and the weak electron–phonon interaction (Huang–Rhys factor S < 1) on the Mn4+ emissive state. Benefiting from the intense ZPL, an ultra-high color rendering index with Ra = 92.7 and R9 = 90.0 is achieved in the w-LED using YAG:Ce3+and NWOF:Mn4+ as color converters, and a wide color gamut of 107.1% NTSC in the w-LED using CsPbBr3 quantum dots and NWOF:Mn4+ is obtained. Herein, we first demonstrate that Mn4+-activated oxyfluorides have great potential in w-LED lighting and display applications. Our study can also enlighten researchers to design highly distorted octahedral sites for Mn4+ doping to achieve an ultra-intense ZPL.

One-Step Synthesis of Stoichiometrically Defined Metal Oxide Nanoparticles at Room Temperature

A great variety of metal oxide nanoparticles have been readily synthesized by using alkali metal oxides, M(2)O (M is Na or Li) and soluble metal salts (metal chlorides) in polar organic solutions, for example, methanol and ethanol, at room temperature. The oxidation states of the metals in the resulting metal oxides (Cu(2)O, CuO, ZnO, Al(2)O(3), Fe(2)O(3), Bi(2)O(3), TiO(2), SnO(2), CeO(2), Nb(2)O(5), WO(3), and CoFe(2)O(4)) range from 1 to 6 and remain invariable through the reactions where good control of stoichiometry is achieved. Metal oxide nanoparticles are 1-30 nm and have good monodispersivity and displayed comparable optical spectra. These syntheses are based on a general ion reaction pathway during which the precipitate occurs when O(2-) ions meet metal cations (M(n+)) in anhydrous solution and the reaction equation is M(n+) + n/2 O(2-) --> MO(n/2) (n=1-6).

Ultra-long metal nanowire arrays on solid substrate with strong bonding

Ultra-long metal nanowire arrays with large circular area up to 25 mm in diameter were obtained by direct electrodeposition on metalized Si and glass substrates via a template-based method. Nanowires with uniform length up to 30 μm were obtained. Combining this deposition process with lithography technology, micrometre-sized patterned metal nanowire array pads were successfully fabricated on a glass substrate. Good adhesion between the patterned nanowire array pads and the substrate was confirmed using scanning acoustic microscopy characterization. A pull-off tensile test showed strong bonding between the nanowires and the substrate. Conducting atomic force microscopy (C-AFM) measurements showed that approximately 95% of the nanowires were electrically connected with the substrate, demonstrating its viability to use as high-density interconnect.