Chia-Liang Sun

The simultaneous electrochemical detection of ascorbic acid, dopamine, and uric acid using graphene/size-selected Pt nanocomposites

In this study, a graphene/Pt-modified glassy carbon (GC) electrode was created to simultaneously characterize ascorbic acid (AA), dopamine (DA), and uric acid (UA) levels via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). During the preparation of the nanocomposite, size-selected Pt nanoparticles with a mean diameter of 1.7 nm were self-assembled onto the graphene surface. In the simultaneous detection of the three aforementioned analytes using CV, the electrochemical potential differences among the three detected peaks were 185 mV (AA to DA), 144 mV (DA to UA), and 329 mV (AA and UA), respectively. In comparison to the CV results of bare GC and graphene-modified GC electrodes, the large electrochemical potential difference that is achieved via the use of the graphene/Pt nanocomposites is essential to the distinguishing of these three analytes. An optimized adsorption of size-selected Pt colloidal nanoparticles onto the graphene surface results in a graphene/Pt nanocomposite that can provide a good platform for the routine analysis of AA, DA, and UA.

Microwave-Assisted Synthesis of a Core–Shell MWCNT/GONR Heterostructure for the Electrochemical Detection of Ascorbic Acid, Dopamine, and Uric Acid

In this study, graphene oxide nanoribbons (GONRs) were synthesized from the facile unzipping of multiwalled carbon nanotubes (MWCNTs) with the help of microwave energy. A core-shell MWCNT/GONR-modified glassy carbon (MWCNT/GONR/GC) electrode was used to electrochemically detect ascorbic acid (AA), dopamine (DA), and uric acid (UA). In cyclic voltammograms, the MWCNT/GONR/GC electrode was found to outperform the MWCNT- and graphene-modified GC electrodes in terms of peak current. For the simultaneous sensing of three analytes, well-separated voltammetric peaks were obtained using a MWCNT/GONR/GC electrode in differential pulse voltammetry measurements. The corresponding peak separations were 229.9 mV (AA to DA), 126.7 mV (DA to UA), and 356.6 mV (AA to UA). This excellent electrochemical performance can be attributed to the unique electronic structure of MWCNTs/GONRs: a high density of unoccupied electronic states above the Fermi level and enriched oxygen-based functionality at the edge of the graphene-like structures, as revealed by X-ray absorption near-edge structure spectroscopy, obtained using scanning transmission X-ray microscopy.

ZAO: an attractive potential substitute for ITO in flat display panels

Al-doped ZnO (ZAO) is an attractive material, as it is cheap and abundant, it is nontoxic, has comparable electrical, optical and infrared (I-R) properties to ITO, is cost-effective and is easy to fabricate. In this paper, ZAO films have been prepared by reactive magnetron sputtering. Their electrical conductivity is shown to be in the region of 10(-4) Omega cm. The influence of the substrate-to-target distance and deposition temperature on the resistivity of ZAO films has been studied. Their IR and optical properties have been investigated with UV-VIS and Fourier transformation IR spectrometry. It was shown that the visible transmittance and IR reflectance of ZAO films deposited on polyester at room temperature are comparable to those of ITO films. ZAO films have n-type conductivity. It was found that by adding Al to ZnO the variation in resistivity of ZAO films was decreased, and was usually no more than 1% at 50-400 degreesC in vacuum and 5% at 50-400 degreesC in air

Ferroelectric characteristics of oriented Pb(Zr1−xTix)O3 films

Pb1.2Zr1−xTix)O3 (PZT) films with a variety of compositions were prepared by spin coating on Pt/Ti/SiO2/Si substrate with sol–gel processing. The roles of composition (phase) and orientation in ferroelectric properties of PZT films have been determined. The Zr-rich PZT films with (111)-oriented PZT films have a higher remanent polarization but also show a higher fatigue rate as compared to (100)-oriented films in both Zr-rich(65/35) and Ti-rich(35/65) PZT compositions. The lower fatigue rate of (100)-oriented film can be attributed to its easier reversible domain-wall motions compared to (111)-oriented PZT films due to the absence of internal field stress and less dependence on electrical field. A mode based on domain-wall contribution instead of film–electrode interface is favored to elucidate the role of orientation in fatigue characteristics of PZT films.

A novel core–shell multi-walled carbon nanotube@graphene oxide nanoribbon heterostructure as a potential supercapacitor material

A novel core–shell heterostructure with multi-walled carbon nanotubes as the core and graphene oxide nanoribbons as the shell (MWCNT@GONR), fabricated by the facile unzipping of MWCNTs with the help of microwave energy, was used as a supercapacitor (SC) electrode material. Graphene nanopowder (GNP) and multi-walled carbon nanotubes (MWCNTs) have also been applied as SC materials for comparison. A smooth surface and a tube-like structure are found for the GNP and MWCNTs, respectively, while for the MWCNT@GONR material, graphene oxide sheet structures are observed on both sides of central nanotube cores that retain their tube-like structure. The specific capacitance is much better for the SC electrode with the MWCNT@GONR (252.4 F g−1) compared to the SC electrodes with commercial MWCNTs (39.7 F g−1) and GNP (19.8 F g−1), as determined using cyclic voltammetry (CV) at a scan rate of 50 mV s−1, which is due to the defective edges of the nanostructures in the former. The SC electrode with the MWCNT@GONR also exhibits good stability and capacitance retention even after 1000 cycles of galvanostatic charge–discharge testing, indicating its potential as a SC material. CV, galvanostatic charge–discharge (GC/D) and electrochemical impedance spectroscopy (EIS) were applied to analyze the SC performance.

A reusable magnetic graphene oxide-modified biosensor for vascular endothelial growth factor detection in cancer diagnosis.

Early cancer diagnosis is critical for the prevention of metastasis. However, simple and efficient methods are needed to improve the diagnosis and evaluation of cancer. Here, we propose a reusable biosensor based on a magnetic graphene oxide (MGO)-modified Au electrode to detect vascular endothelial growth factor (VEGF) in human plasma for cancer diagnosis. In this biosensor, Avastin is used as the specific biorecognition element, and MGO is used as the carrier for Avastin loading. The use of MGO enables rapid purification due to its magnetic properties, which prevents the loss of bioactivity. Moreover, the biosensor can be constructed quickly, without requiring a drying process, which is convenient for proceeding to detection. Our reusable biosensor provides the appropriate sensitivity for clinical diagnostics and has a wide range of linear detection, from 31.25-2000 pg mL(-1), compared to ELISA analysis. In addition, in experiments with 100% serum from clinical samples, readouts from the sensor and an ELISA for VEGF showed good correlation within the limits of the ELISA kit. The relative standard deviation (RSD) of the change in current (ΔC) for reproducibility of the Au biosensor was 2.36% (n=50), indicating that it can be reused with high reproducibility. Furthermore, the advantages of the Avastin-MGO-modified biosensor for VEGF detection are that it provides an efficient detection strategy that not only improves the detection ability but also reduces the cost and decreases the response time by 10-fold, indicating its potential as a diagnosis product.

Graphene Nanoribbon-Supported PtPd Concave Nanocubes for Electrochemical Detection of TNT with High Sensitivity and Selectivity

In this work, PtPd concave nanocubes anchored on graphene nanoribbons (PtPd-rGONRs) were successfully fabricated through a hydrothermal process. The structural characterizations confirmed that PtPd concave cubes with an average size of around 11 nm have been successfully synthesized and they are uniformly assembled on the surface of rGONRs. The electrochemical measurements demonstrated that the PtPd-rGONRs composite-modified glassy carbon electrode (GCE) shows much enhanced current signals for TNT reduction, which is 4 and 12-fold higher than rGONRs and bare glassy carbon electrode, respectively. The PtPd-rGONRs exhibited a wide linear range for TNT detection from 0.01 to 3 ppm with the sensing limit of 0.8 ppb. Moreover, the PtPd-rGONRs showed excellent detection stability for the determination of TNT. Most importantly, the PtPd-rGONRs-based electrochemical detection platform can be successfully applied to TNT detection in tap water and real lake water samples. The present study indicates that graphene nanoribbon-supported nanocrystals are promising in designing high performance electrochemical sensors for explosives detection.

Effect of annealing temperature on physical and electrical properties of Bi3.25La0.75Ti3O12 thin films on Al2O3-buffered Si

The effect of annealing temperature, especially at high temperatures, on the physical and electrical properties of Bi3.25La0.75Ti3O12 (BLT) thin films on Al2O3 (10 nm)/Si has been investigated. The width of memory window in capacitance–voltage curves for BLT/Al2O3/Si capacitors annealed at temperature range of 700 °C–950 °C increases with increasing annealing temperature. At the highest annealing temperature of 950 °C, a large ferroelectric memory window of 13 V is obtained under ±15 V sweep voltage, and this large ferroelectric memory window should be related to the reduced leakage current. Owing to the excellent electrical properties, the high-temperature stable BLT/Al2O3/Si capacitor is compatible with current very large scale integrated technology process.

Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Scanning transmission X-ray microscopy (STXM) has been used to chemically image single and multiple layers of a thermally reduced graphene oxide (r-GO) multi-layer sheet of the size of ∼1 μm and a thickness of ∼5 nm. The thickness of individual layers in the single sheet can be identified through quantitative analysis of STXM. The local electronic and chemical structure of interest (edge versus center) in different regions within the single r-GO sheet has been studied by C K-edge X-ray absorption near edge structure spectroscopy (XANES) with 30 nm spatial resolution. High and localized unoccupied densities of states (DOS) of carbon σ* character were observed in r-GO compared to graphite and were interpreted as the lack of strong layer to layer interaction in the former. The azimuthal dependence of C K-edge XANES in selected locations has also been obtained and was used to infer the preferred edge structure. The r-GO sample was also characterized by TEM, AFM and Raman spectroscopy; the findings are in good accord with the STXM results.

Wear-resistant multilayered diamond-like carbon coating prepared by pulse biased arc ion plating

Diamond-like carbon coatings have been deposited by a pulse biased arc ion plating. In order to improve their adherence to metal substrate, two systems of graded transition layers, namely Ti/TiN/TiC and Ti/TiCN/TIC, have been applied. The structure and composition of the diamond-like carbon/transition composite coatings were studied by scanning electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The total thickness of the coatings was within a range of 1.0-2.0 mum. Such multi-layer coatings showed excellent properties including high hardness, low friction coefficient and long wear-resistant lifetime. Diamond like carbon coatings as well as their wear tracks developed by sliding steel balls have been investigated by scanning electron microscopy. The results of the analysis, particularly that of the tribological study showed that the wear resistance and film-to-substrate adherence of diamond like carbon coatings with stainless steel surface were dramatically improved by using a graded transition layer and pulse biased arc ion plating