Zhenyu Chu

Subnanometer Two-Dimensional Graphene Oxide Channels for Ultrafast Gas Sieving

Two-dimensional (2D) materials with atomic thickness and extraordinary physicochemical properties exhibit unique mass transport behaviors, enabling them as emerging nanobuilding blocks for separation membranes. Engineering 2D materials into membrane with subnanometer apertures for precise molecular sieving remains a great challenge. Here, we report rational-designing external forces to precisely manipulate nanoarchitecture of graphene oxide (GO)-assembled 2D channels with interlayer height of ∼0.4 nm for fast transporting and selective sieving gases. The external forces are synergistic to direct the GO nanosheets stacking so as to realize delicate size-tailoring of in-plane slit-like pores and plane-to-plane interlayer-galleries. The 2D channels endow GO membrane with excellent molecular-sieving characteristics that offer 2-3 orders of magnitude higher H2 permeability and 3-fold enhancement in H2/CO2 selectivity compared with commercial membranes. Formation mechanism of 2D channels is proposed on the basis of the driving forces, nanostructures, and transport behaviors.

An ultrasensitive electrochemical sensing platform for Hg2+ based on a density controllable metal-organic hybrid microarray.

A novel electrochemical Hg(2+) biosensor was developed on the basis of a metal-organic hybrid microarray, in which the nicking endonuclease (NE) assisted target-triggered strand release strategy was realized via the DNA cyclic amplification technique. The metal-organic hybrid microarray was fabricated using the SAM of 1, 4-benzenendithiol as soft template, and the density of the microarray could be adjusted by controlling the surface coverage of 1,4-benzenendithiol molecules. In the presence of Hg(2+), capture DNA (cDNA) with an indicator at one end could hybridize with the reporter DNA (rDNA) through the stable T-Hg(2+)-T linkage, forming the nicking recognition site. After the nicking reaction, the electrochemical indicator dissociated from the electrode surface. The released rDNA and Hg(2+) could be reused in the sensing system and initiate the next cycle, and more electroactive indicator dissociated from the electrode surface, resulting in a significant signal decrease. The constructed DNA biosensor could detect Hg(2+) in a wide linear range from 15 pM to 500 nM, with an ultrasensitive detection limit of 5 pM (S/N=3). Furthermore, the biosensor exhibited excellent stability, good reproducibility and high selectivity towards other divalent ions. The proposed sensing system also showed a promising potential for the application in real aquatic product sample analysis.

Template-free growth of regular nano-structured Prussian blue on a platinum surface and its application in biosensors with high sensitivity

Prussian blue (PB) is considered as a promising material for electrochemical biosensors. However, the PB microstructure, which is essential for biosensor performance, is difficult to control on the electrode surface due to its rapid formation reaction. In this report, the growth of a regular nano-structured PB on the platinum (Pt) electrode surface was realized by an aerosol deposition approach without a template. The morphology of PB could be controlled well via deposition time and temperature, as characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The cuboid and cubic shapes of PB nano-crystals were formed at 25 and 35 °C, respectively. When the Pt electrode with nano-cubic PB was used to detect hydrogen peroxide, it exhibited a high sensitivity (1163 mA M−1 cm−2) and an excellent anti-interference to ascorbic acid. Our observations suggest that the proposed approach may be used for regular growth of crystals having rapid formation reaction, and the prepared amperometric biosensor will have potential applications in the detection of physiological substances.

Facile synthesis of hierarchically aloe-like gold micro/nanostructures for ultrasensitive DNA recognition

Well-defined hierarchically aloe-like gold micro/nanostructures (HAG) are one-step electrochemically fabricated without introducing any template or surfactant. The formation kinetics of the HAG can be described as a nucleation and three-dimensional growth process controlled by the reactant diffusion from the solution side. As the applied electro-deposition potential moved in the negative direction, the gold crystal density increased, and the crystal shape changed from a quasi-spherical to dendritic fractal morphology. Under the optimal potential of -0.1 V and the time of 10 min, well-defined HAG possessing a hydrophilic surface with large effective area (ca. 8 times of its geometrical area) were obtained, which was used as the substrate for fabricating an ultrasensitive DNA biosensor. The DNA biosensor displayed a significantly enhanced detection limit of 12 aM, a wide linear response from 50 aM to 1 pM, as well as good selectivity, stability and reusability. This efficient DNA molecule immobilization platform may have implications in the preparation of many other gold micro/nanostructures (GMNs) with interesting properties and application potentials in many fields, such as biosensing, biocatalysis and biofuel cells.

CO2-tolerant oxygen-permeable perovskite-type membranes with high permeability

There is a desire for CO2-tolerant oxygen-permeable membranes for CO2 capture based on the oxyfuel process. Here we report a general doping strategy for developing CO2-tolerant SrFeO3−δ-based oxygen-permeable membranes. To combine excellent CO2 tolerance and high permeability, two novel CO2-tolerant oxygen-permeable membranes of SrFe0.9Ta0.1O3−δ (SFT) and SrFe0.8Sb0.2O3−δ (SFS) have been developed based on this doping strategy. Both SFT and SFS oxides possessed high phase stability especially in a pure CO2 atmosphere for 96 h at 1173 K. The high CO2-tolerant properties were mainly associated with high acidity, high valence and appropriate ionic radius of the Ta or Sb cation and high average metal bond energy of SFT or SFS oxide. Both SFT and SFS disk membranes (1 mm-thick) with low oxygen permeation activation energies exhibited high oxygen permeation fluxes of 0.3 and 0.22 ml min−1 cm−2, respectively, which were unchanged during the long-term operation (130 h) under air/CO2 gradient at 1173 K. Furthermore, the highest oxygen permeation flux of 1.15 ml min−1 cm−2 through the SFT multichannel hollow fiber (MHF) membrane at 1173 K under air/CO2 gradient can meet the requirement of commercial application in the oxyfuel process. The present results would give guidance for the design of CO2-tolerant SF-based membranes.

Single layer Prussian blue grid as a versatile enzyme trap for low-potential biosensors

A single layer Prussian blue (PB) grid was constructed on a Pt substrate using a self-assembly approach with nanosphere lithography in order to create a matrix for the uniform and ordered immobilization of proteins. Enzymes were captured in the cavities of the PB grid with the aid of an alkoxy silane linker, which enabled strong interaction between the silanes alkoxy groups and Pt. Using a low applied potential of −0.1 V vs. Ag/AgCl the as-prepared biosensors exhibited excellent performance in the detection of glucose, lactate and glutamate, indicating the versatile application of this specific PB architecture in the area of biosensors.

Facile fabrication of a Prussian Blue film by direct aerosol deposition on a Pt electrode

A facile aerosol deposition approach, which was simulated as feasible by density functional theory (DFT), was applied to synthesize a Prussian Blue (PB) film directly on a Pt electrode surface.

A facile and green strategy for preparing newly-designed 3D graphene/gold film and its application in highly efficient electrochemical mercury assay

In this work, we report a facile and green strategy for in situ and one step preparation of a novel 3D graphene/gold (G/Au) film. Triggering with unique driving force from hydrothermal growth, a 3D interlaced graphene framework with hierarchically porous structures was directly attached on a gold substrate pretreated with a self-assembled monolayer. Simultaneously, highly dispersive Au nanoparticles with tunable morphologies were anchored on the framework utilizing generated graphene as an endogenous reductant. Newly-designed 3D G/Au film possessed excellent properties of significantly large specific area, good electrical conductivity, high structure stability and substrate binding strength, etc. As a paradigm, an electrochemical Hg2+ biosensor was constructed on 3D G/Au film, in which an exonuclease III-assisted target recycling was introduced. Impressively, an ultralow detection limit of 50 aM (S/N=3), a wide linear range from 0.1 fM to 0.1μM, a high selectivity and a good reliability for Hg2+ assay in real water and serum samples were realized using prepared biosensor. It is highly envisioned that this work opens the door towards simply fabricating varying types of 3D graphene based hybrid films, and such G/Au film will have widespread applications in electroanalysis and electrocatalysis.

In-situ growth of micro-cubic Prussian blue–TiO2 composite film as a highly sensitive H2O2 sensor by aerosol co-deposition approach

Assisted by the aerosol co-deposition approach, Prussian blue (PB)-TiO2 composite film can be in-situ formed in one step. The architecture of this film is constructed by two layers: PB-TiO2 nano-particles as a ground layer and individual PB micro-cubes as a top layer. Together with the strong electrocatalytic ability from regular PB morphology, TiO2 can denote its high catalysis in H2O2 detection attributed by the extinction of band gap since the combination of PB. Under a low operation potential -0.05V, this sensor exhibits an ultrasensitive ability (1726.8μAmM(-1)cm(-2)), stability and low detection limit (1.5μM) in H2O2 analysis. The application of this composite material is hopeful to extend in complex physiological analysis, and the preparation approach is promising to extend in more composite materials in-situ synthesis.

Facile fabrication of a three-dimensional gold nanowire array for high-performance electrochemical sensing

Great challenges remain in the template-assisted fabrication of metal nanowire arrays on substrates, because enormous effort is required to address the adhesion issues between substrates and adopted templates, e.g. anodic aluminum oxide (AAO). Therefore, novel and promising templates are highly desired for the construction of proposed structures. Here, vertical 1,5-diaminoanthraquinone (DAAQ) nanowires were prepared in situ on substrates by a facile method, and these were proven to be a reliable and alternative template for the preparation of a metal nanowire array. As an example, with the wet chemical reduction of HAuCl4, a three-dimensional gold nanowire array (3D GNA) was successfully obtained with a DAAQ template. The proposed 3D GNA has an extremely large roughness factor of ca. 15, as well as high stability and a favorable surface structure for the diffusion of analytes, making it a suitable candidate for the construction of high-performance electrochemical biosensors. As a result, an ultrasensitive aptasensor was constructed for the detection of thrombin, with a general sensing scheme. The fabricated aptasensor displays an impressively ultralow detection limit of 3 fM (S/N = 3) with a wide linear response from 10 fM to 1 nM, as well as excellent selectivity, good reproducibility and acceptable stability. Further, the biosensor exhibits potential for application in the analysis of real serum samples. The developed DAAQ nanowires are envisaged to become a general template for the fabrication of more nanowire arrays and the as-synthesized 3D GNA could open up a wide range of possibilities for potential applications in biological sensing.