Xiaoxue Xu

Bioelectrochemistry of hemoglobin immobilized on a sodium alginate-multiwall carbon nanotubes composite film

This study described the bioelectrochemistry of hemoglobin (Hb) at multiwall carbon nanotubes (MWCNTs) noncovalently functionalized with biopolymers of sodium alginate (SA). The characteristics of Hb/SA-MWCNTs composite film were studied by using FT-IR spectroscopy, UV-vis spectroscopy and electrochemical methods. Hb immobilized on SA-MWCNTs composite film retained its native secondary structure, achieved direct electron transfer with the apparent heterogeneous electron transfer rate constant (k(s)) of (9.54+/-0.883) s(-1) and showed excellent bioelectrocatalytic activity to the reduction of hydrogen peroxide. The amperometric response of the biosensor varied linearly with the H(2)O(2) concentration ranging from 40 to 200 microM, with a detection limit of 16.41x10(-6) M (S/N=3) and the good long-term stability. Finally, we applied this proposed method to investigate the concentration of hydrogen peroxide in real samples.

Preparation and characterization of electrospun PLGA/gelatin nanofibers as a potential drug delivery system

Drug (Fenbufen, FBF)-loaded poly(D,L-lactide-co-glycolide) (PLGA) and PLGA/gelatin nanofibrous scaffolds were fabricated via electrospinning technique. The influences of gelatin content, fiber arrangement, crosslinking time and pH value of the buffer solution on FBF release behavior of the resulting nanofibrous scaffolds were investigated, with the corresponding FBF-loaded PLGA and PLGA/gelatin solvent-cast films as controls. The release rate of FBF was found to be increased with the increment of gelatin content for all the composite samples, and the FBF release rate of aligned nanofibrous scaffold was lower than that of randomly oriented scaffold. Moreover, the crosslinking treatment depressed effectively the burst release of FBF at initial release stage of PLGA/gelatin (9/1) nanofibrous scaffold. In addition, the pH value of the buffer solution could change the physical state of the polymer and affect the FBF release rate.

Three-dimensional controlled growth of monodisperse sub-50 nm heterogeneous nanocrystals

The ultimate frontier in nanomaterials engineering is to realize their composition control with atomic scale precision to enable fabrication of nanoparticles with desirable size, shape and surface properties. Such control becomes even more useful when growing hybrid nanocrystals designed to integrate multiple functionalities. Here we report achieving such degree of control in a family of rare-earth-doped nanomaterials. We experimentally verify the co-existence and different roles of oleate anions (OA−) and molecules (OAH) in the crystal formation. We identify that the control over the ratio of OA− to OAH can be used to directionally inhibit, promote or etch the crystallographic facets of the nanoparticles. This control enables selective grafting of shells with complex morphologies grown over nanocrystal cores, thus allowing the fabrication of a diverse library of monodisperse sub-50 nm nanoparticles. With such programmable additive and subtractive engineering a variety of three-dimensional shapes can be implemented using a bottom–up scalable approach.

Phase formation of Ni–Ti via solid state reaction

Phase formation of NiTi alloys via solid-state diffusion reactions is investigated. Samples of different Ni–Ti compositions were synthesized from elemental powders. The study revealed that the sintered samples consisted of Ti(Ni), NiTi2, NiTi and Ni3Ti in co-existence. Such co-existence is not expected from the equilibrium phase diagram, but can be explained in terms of Ni/Ti inter-diffusion processes. Thermodynamic analysis indicates that formation of NiTi is not favoured in primary reactions between Ni and Ti, but can be formed via secondary reactions involving primary reaction products of NiTi2 and Ni3Ti. Such reactions are difficult in solid state due to the difficulties of long-distance diffusion required. The synthesized alloys were found to exhibit much reduced martensitic transformation intensity, implying low transformation volume.

A novel amperometric hydrogen peroxide biosensor based on immobilized Hb in Pluronic P123-nanographene platelets composite

In this paper, an amperometric biosensor of hydrogen peroxide (H(2)O(2)) was fabricated by immobilization of Hemoglobin (Hb) on a Pluronic P123-nanographene platelet (NGP) composite. Direct electron transfer in the Hb-immobilized P123-NGP composite film was greatly facilitated. The surface concentration (Γ*) and apparent heterogeneous electron transfer rate constant (k(s)) were calculated to be (1.60±0.17)×10(-10) mol cm(-2) and 48.51 s(-1), respectively. In addition, the Hb/Pluronic P123-NGP composite showed excellent bioelectrocatalytic activity toward the reduction of H(2)O(2). The biosensor of H(2)O(2) exhibited a linear response to H(2)O(2) in the range of 10-150 μM and a detection limit of 8.24 μM (S/N=3) was obtained. The apparent Michaelis-Menten constant (K(m)(app)) was 45.35 μM. The resulting biosensor showed fast amperometric response, with very high sensitivity, reliability and effectiveness.

Carbon nanotube-hydroxyapatite-hemoglobin nanocomposites with high bioelectrocatalytic activity.

In this paper, carbon nanotubes-hydroxyapatite (MWCNTs-HA) composite were synthesized by self-assembling technique, and investigated by X-ray diffraction, scanning electron microscopy (SEM) and FT-IR spectroscopy. Hemoglobin (Hb) immobilized in MWCNTs-HA film not only retained its similarly native conformations, but also achieved the direct electron transfer. The apparent heterogeneous electron transfer rate constant (k(s)) was evaluated as (5.05+/-0.41) s(-1) according to Lavirons equation, and the surface coverage (Gamma*) was estimated as (9.25+/-0.69)x10(-10)mol cm(-2). Moreover, the Hb immobilized in MWCNTs-HA film exhibited remarkable bioelectrocatalytic activity for the electrochemical reduction of H(2)O(2). The amperometric response of the biosensor varied linearly with the H(2)O(2) concentration ranging from 0.5microM to 2microM, and the results showed a detection limit of 0.09microM. Furthermore, the Hb-immobilized MWCNTs-HA film exhibited the excellent catalytic reactivity toward trichloroacetic acid (TCA).

Electrospun Chitosan-graft-PLGA nanofibres with significantly enhanced hydrophilicity and improved mechanical property

This work reported a novel poly(lactic-co-glycolic acid) (PLGA) composite nanofibres, Chitosan-graft-PLGA (CS-graft-PLGA), produced by the electrospinning technique. CS was grafted onto the PLGA surface via the cross-linking agents reacting with the PLGA with reactive carboxyl groups on its surfaces introduced from the alkali treatment. The CS grafting ratios of the electrospun CS-graft-PLGA nanofibres were about 2.43%, 4.34%, 16.97% and 39.4% after cross-linked for 12 h, 16 h, 20 h and 24 h, respectively. The electrospun CS-graft-PLGA nanofibres were significantly uniform and highly smooth without the occurrence of bead defects, even at high CS grafting ratio. The electrospun CS-graft-PLGA nanofibres not only possessed the improved hydrophilicity and the protein absorption property, but also maintained the good mechanical property. In addition, the CS grafting can be conducive to accelerate degradation rate of PLGA.

Self-assembled structures of CuO primary crystals synthesized from Cu(CH3COO)2–NaOH aqueous systems

This paper reports self-assembled microstructures of CuO particles synthesized from Cu(CH3COO)2–NaOH aqueous systems. The assembled CuO particles are composed of CuO primary single crystal nanoparticles, which are bounded by three {100} planes. The morphology of these CuO primary crystals is determined by the surface energy of the exterior crystallographic planes and influenced by NaOH concentration in the solution. The electrical polarity on opposite surfaces of the {100}-CuO primary crystals facilitates their self-aligned assembly into various microstructures. Depending on the NaOH concentration in the solution, different 3D or 2D structures of CuO particles are formed, including lenticular plates, elliptical plates and pseudo-3D structures, as influenced by selective adsorption of OH− ions on the exterior crystal planes of CuO primary crystals.

A novel amperometric hydrogen peroxide biosensor based on electrospun Hb–collagen composite

In this paper, the hemoglobin (Hb)-collagen microbelt modified electrode with three-dimensional configuration was fabricated via the electrospinning method. Direct electron transfer of the Hb immobilized into the electrospun collagen microbelts was greatly facilitated. The apparent heterogeneous electron transfer rate constant (k(s)) was calculated to be 270.6s⁻¹. The electrospun Hb-collagen microbelt modified electrode showed an excellent bioelectrocatalytic activity toward the reduction of H₂O₂. The amperometric response of the biosensor varied linearly with the H₂O₂ concentration ranging from 5 × 10⁻⁶molL⁻¹ to 30×10⁻⁶molL⁻¹, with a detection limit of 0.37 × 10⁻⁶molL⁻¹ (signal-to-noise ratio of 3). The apparent Michaelis-Menten constant (K(m)(app)) was 77.7 μmolL⁻¹. The established biosensor exhibited fast amperometric response, high sensitivity, good reproducibility and stability.

Aligned Nanofibers from Polypyrrole/Graphene as Electrodes for Regeneration of Optic Nerve via Electrical Stimulation

The damage of optic nerve will cause permanent visual field loss and irreversible ocular diseases, such as glaucoma. The damage of optic nerve is mainly derived from the atrophy, apoptosis or death of retinal ganglion cells (RGCs). Though some progress has been achieved on electronic retinal implants that can electrically stimulate undamaged parts of RGCs or retina to transfer signals, stimulated self-repair/regeneration of RGCs has not been realized yet. The key challenge for development of electrically stimulated regeneration of RGCs is the selection of stimulation electrodes with a sufficient safe charge injection limit (Q(inj), i.e., electrochemical capacitance). Most traditional electrodes tend to have low Q(inj) values. Herein, we synthesized polypyrrole functionalized graphene (PPy-G) via a facile but efficient polymerization-enhanced ball milling method for the first time. This technique could not only efficiently introduce electron-acceptor nitrogen to enhance capacitance, but also remain a conductive platform-the π-π conjugated carbon plane for charge transportation. PPy-G based aligned nanofibers were subsequently fabricated for guided growth and electrical stimulation (ES) of RGCs. Significantly enhanced viability, neurite outgrowth and antiaging ability of RGCs were observed after ES, suggesting possibilities for regeneration of optic nerve via ES on the suitable nanoelectrodes.