Liangsheng Hu

One-step growth and field emission properties of quasialigned TiO2 nanowire/carbon nanocone core-shell nanostructure arrays on Ti substrates

Quasialigned nanoarrays consisting of TiO2 nanowire cores and carbon nanocone shells have been produced directly on titanium foils via a simple one-step thermal reaction under acetone vapor at 850°C. The nanowire cores are single-crystalline rutile TiO2 with diameters of 15–20nm and the conical carbon shells are amorphous with gradually decreasing thicknesses from 200–300nm at the bases to 5–10nm at the tips. Disparity of precipitation and etching of carbon shell give rise to the conical shape. Such TiO2∕C nanocone arrays on a conducting substrate are a new member of the conical nanostructures and promising field electron emitters.

Mechanism of cell repellence on quasi-aligned nanowire arrays on Ti alloy

Cell-repelling structures are often required in biosensors, bioelectronics, and drug delivery systems, but the search for satisfactory cell-repelling structures with good biocompatibility and long-term stability is challenging. In this work, two types of quasi-aligned nanowire arrays (QANWA) with different surface chemistry but similar surface topography, namely titanium carbide-carbon core-shell (TiC/C) and titania (TiO(2)), are fabricated on Ti6Al4V. Both QANWAs inhibit cell adhesion consequently leading to cell apoptosis possibly due to disruption in the adhesion assembly. Other cell functions such as proliferation and differentiation as monitored by extracellular matrix secretion and mineralization are also substantially depressed. The cell-repelling property is related to the nanostructure but independent of the surface chemistry and surface wettability. It is also not related to protein adsorption which is in fact slightly enhanced on the nanowire arrays. The QANWAs can be modified to have a larger loading capacity thereby enhancing the controlled release kinetics in drug delivery applications and to resist protein adsorption resulting in better biosensor performance. This concept which can be readily extended to other types of QANWAs and biomaterials has broad clinical potential.

Recyclable and high-sensitivity electrochemical biosensing platform composed of carbon-doped TiO2 nanotube arrays.

Electrode fouling and passivation are the main reasons for attenuated signals as well as reduced sensitivity and selectivity over time in electrochemical analysis. We report here a refreshable electrode composed of carbon-doped TiO(2) nanotube arrays (C-doped TiO(2)-NTAs), which not only has excellent electrochemical activity for simultaneous determination of 5-hydroxytryptamine and ascorbic acid but also can be easily photocatalytically refreshed to maintain the high selectivity and sensitivity. The C-doped TiO(2)-NTAs are fabricated by rapid annealing of as-anodized TiO(2)-NTAs in argon. The residual ethylene glycol absorbed on the nanotube wall acts as the carbon source and no foreign carbon precursor is thus needed. The morphology, structure, and composition the C-doped TiO(2)-NTAs are determined, and the corresponding doping mechanism is investigated by thermal analysis and in situ mass spectroscopy. Because of the high photocatalytic activity of the C-doped TiO(2)-NTAs electrode, the electrode surface can be readily regenerated by ultraviolet or visible light irradiation. This photoassisted regenerating technique does not damage the electrode microstructure while rendering high reproducibility and stability.

AU nanoparticles decorated TiO2 nanotube arrays as a recyclable sensor for photoenhanced electrochemical detection of Bisphenol A

A photorefreshable and photoenhanced electrochemical sensing platform for bisphenol A (BPA) detection based on Au nanoparticles (NPs) decorated carbon doped TiO2 nanotube arrays (TiO2/Au NTAs) is described. The TiO2/Au NTAs were prepared by quick annealing of anodized nanotubes in argon, followed by controllable electrodeposition of Au NPs. The decoration of Au NPs not only improved photoelectrochemical behavior but also enhanced electrocatalytic activities of the resulted hybrid NTAs. Meanwhile, the high photocatalytic activity of the NTAs allowed the electrode to be readily renewed without damaging the microstructures and surface states after a short UV treatment. The electrochemical detection of BPA on TiO2/Au NTAs electrode was significantly improved under UV irradiation as the electrode could provide fresh reaction surface continuously and the further increased photocurrent resulting from the improved separation efficiency of the photogenerated electron-hole pairs derived from the consumption of holes by BPA. The results showed that the refreshable TiO2/Au NTAs electrode is a promising sensor for long-term BPA monitoring with the detection limit (S/N = 3) of 6.2 nM and the sensitivity of 2.8 μA·μM(-1)·cm(-2).

Real-Time Monitoring of Auxin Vesicular Exocytotic Efflux from Single Plant Protoplasts by Amperometry at Microelectrodes Decorated with Nanowires†

Recent biochemical results suggest that auxin (IAA) efflux is mediated by a vesicular cycling mechanism, but no direct detection of vesicular IAA release from single plant cells in real-time has been possible up to now. A TiC@C/Pt-QANFA micro-electrochemical sensor has been developed with high sensitivity in detection of IAA, and it allows real-time monitoring and quantification of the quantal release of auxin from single plant protoplast by exocytosis.

Hydrothermal synthesis of perovskite-type MTiO3 (M = Zn, Co, Ni)/TiO2 nanotube arrays from an amorphous TiO2 template

Ordered perovskite-type MTiO3/TiO2 nanotube arrays (NTAs) (M = Zn, Co, Ni) are prepared by a general hydrothermal route based on amorphous TiO2 NTAs via electrochemical anodization of Ti foil. The as-anodized amorphous TiO2 is not stable and can react with H2O in solution producing soluble Ti(OH)62− to form anatase nanoparticles (NPs) via water-induced dissolution and recrystallization. The pH and salt content in the solution play important roles in the morphology and composition of the hydrothermal products. In the presence of a metal acetate, the reaction between Ti(OH)62− and H+ is dramatically restricted and the reaction proceeds preferentially between Ti(OH)62− and M2+ (M = Zn, Co, Ni) to produce insoluble MTiO3 NPs which adhere onto the original architecture in situ to form perovskite-type MTiO3/TiO2 NTAs. This study elucidates the role of the amorphous structure in the formation of MTiO3 and provides a general means of synthesizing nanostructured MTiO3.

Label-free detection of endocrine disrupting chemicals by integrating a competitive binding assay with a piezoelectric ceramic resonator

A piezoelectric biosensor for detection of endocrine disrupting chemicals (EDCs) was developed by incorporating chemical/biochemical recognition elements on the ceramic resonator surface for competitive binding assays. A facile electrodeposition was employed to modify the sensor surface with Au nanoparticles, which increased the surface area and enhanced the binding capacity of the immobilized probes. Thiol-labeled long chain hydrocarbon with bisphenol A (BPA) as head group was synthesized and self-assembled on the Au nanoparticle surface as the sensing probes, which showed a linear response upon the binding of estrogen receptor (ER-α) ranging from 1 to 30 nM. Detection of estrone, 17β-estradiol and BPA was achieved by integrating a competitive binding assay with the piezoelectric sensor. In this detection scheme, different concentrations of EDCs were incubated with 30 nM of ER-α, and the un-bounded ER-α in the solution was captured by the probes immobilized on the ceramic resonator, which resulted in the frequency changes for different EDCs. The biosensor assay exhibited a linear response to EDCs with a low detection limit of 2.4-2.9 nM (S/N=3), and required only a small volume of sample (1.5 µl) with the assay time of 2h. The performance of the biosensor assay was also evaluated for rapid and facile determination of EDCs of environmental relevant concentrations in drinking water and seawater, and the recovery rate was in the range between 94.7% and 109.8%.

Cu 2 ZnSnS 4 /MoS 2 -Reduced Graphene Oxide Heterostructure: Nanoscale Interfacial Contact and Enhanced Photocatalytic Hydrogen Generation

Hydrogen generation from water using noble metal-free photocatalysts presents a promising platform for renewable and sustainable energy. Copper-based chalcogenides of earth-abundant elements, especially Cu2ZnSnS4 (CZTS), have recently arisen as a low-cost and environment-friendly material for photovoltaics and photocatalysis. Herein, we report a new heterostructure consisting of CZTS nanoparticles anchored onto a MoS2-reduced graphene oxide (rGO) hybrid. Using a facile two-step method, CZTS nanoparticles were in situ grown on the surface of MoS2-rGO hybrid, which generated high density of nanoscale interfacial contact between CZTS and MoS2-rGO hybrid. The photoexcited electrons of CZTS can be readily transported to MoS2 through rGO backbone, reducing the electron-hole pair recombination. In photocatalytic hydrogen generation under visible light irradiation, the presence of MoS2-rGO hybrids enhanced the hydrogen production rate of CZTS by 320%, which can be attributed to the synergetic effect of increased charge separation by rGO and more catalytically active sites from MoS2. Furthermore, this CZTS/MoS2-rGO heterostructure showed much higher photocatalytic activity than both Au and Pt nanoparticle-decorated CZTS (Au/CZTS and Pt/CZTS) photocatalysts, indicating the MoS2-rGO hybrid is a better co-catalyst for photocatalytic hydrogen generation than the precious metal. The CZTS/MoS2-rGO system also demonstrated stable photocatalytic activity for a continuous 20 h reaction.

Controllable Growth of Conical and Cylindrical TiO2–Carbon Core–Shell Nanofiber Arrays and Morphologically Dependent Electrochemical Properties

Quasi-aligned cylindrical and conical core-shell nanofibers consisting of carbon shells and TiO(2) nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO(2) nanowire core 30-50 nm in diameter and a 5-10 nm-thick cylindrical carbon shell, while in the conical nanostructure the TiO(2) nanowire core has a diameter of 20-40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well-defined redox peaks of the [Fe(CN)(6)](3-/4-) redox couple and heterogeneous charge-transfer rate constants of 0.010 and 0.062 cm  s(-1) for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge-plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge-plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance.

An antibacterial platform based on capacitive carbon-doped TiO2 nanotubes after direct or alternating current charging

Electrical interactions between bacteria and the environment are delicate and essential. In this study, an external electrical current is applied to capacitive titania nanotubes doped with carbon (TNT-C) to evaluate the effects on bacteria killing and the underlying mechanism is investigated. When TNT-C is charged, post-charging antibacterial effects proportional to the capacitance are observed. This capacitance-based antibacterial system works well with both direct and alternating current (DC, AC) and the higher discharging capacity in the positive DC (DC+) group leads to better antibacterial performance. Extracellular electron transfer observed during early contact contributes to the surface-dependent post-charging antibacterial process. Physiologically, the electrical interaction deforms the bacteria morphology and elevates the intracellular reactive oxygen species level without impairing the growth of osteoblasts. Our finding spurs the design of light-independent antibacterial materials and provides insights into the use of electricity to modify biomaterials to complement other bacteria killing measures such as light irradiation.Bacteria are known to be sensitive to electrical interactions with the environment. Here, the authors report on a study into how the antibacterial properties of carbon-doped titania nanotubes are affected by capacitance after charging with direct and alternating currents.