Qiuping Wei

Hall effect biosensors with ultraclean graphene film for improved sensitivity of label-free DNA detection.

The quality of graphene strongly affects the performance of graphene-based biosensors which are highly demanded for the sensitive and selective detection of biomolecules, such as DNA. This work reported a novel transfer process for preparing a residue-free graphene film using a thin gold supporting layer. A Hall effect device made of this gold-transferred graphene was demonstrated to significantly enhance the sensitivity (≈ 5 times) for hybridization detection, with a linear detection range of 1pM to 100nM for DNA target. Our findings provide an efficient method to boost the sensitivity of graphene-based biosensors for DNA recognition.

ENHANCED NUCLEATION AND SMOOTHNESS OF NANOCRYSTALLINE DIAMOND FILMS VIA W-C GRADIENT INTERLAYER

CVD diamond coating was deposited on to 13%wt. Co-containing tungsten cemented carbide surfaces using a hot filament chemical vapor deposition (HFCVD) to improve wear properties and performance of WC-13%wt.Co. Prior to the deposition of the diamond films, a W-C gradient intermediate layer had been sputtered on WC-13%wt.Co. The surface and cross-section morphology, phase transformation, and grain size distribution of the samples were investigated by means of field emission scanning electron microscope (SEM), X-ray diffractometer (XRD), and atomic force microscope (AFM), respectively. The results show that W-C gradient intermediate layers can effectively reduce the diffusion of Co in cemented carbide substrates during diamond deposition process, resulting high nucleation density and ultra smooth nanocrystalline diamond films.

Effects of sputtering pressure on nanostructure and nanomechanical properties of AlN films prepared by RF reactive sputtering

Wurtzite aluminum nitride (AlN) films were deposited on Si(100) wafers under various sputtering pressures by radio-frequency (RF) reactive magnetron sputtering. The film properties were investigated by XRD, SEM, AFM, XPS and nanoindenter techniques. It is suggested from the XRD patterns that highly c-axis oriented films grow preferentially at low pressures and the growth of (100) planes are preferred at higher pressures. The SEM and AFM images both reveal that the deposition rate and the surface roughness decrease while the average grain size increases with increasing the sputtering pressure. XPS results show that lowering the sputtering pressure is a useful way to minimize the incorporation of oxygen atoms into the AlN films and hence a film with closer stoichiometric composition is obtained. From the measurement of nanomechanical properties of AlN thin films, the largest hardness and elastic modulus are obtained at 0.30 Pa.

Enhancement of nucleation of diamond films deposited on copper substrate by nickel modification layer

A Ni layer with a thickness of about 100 nm was sputtered on Cu substrates, followed by an ultrasonic seeding with nanodiamond suspension. High-quality diamond film with its crystalline grains close to thermal equilibrium shape was deposited on Cu substrates by hot-filament chemical vapor deposition (HF-CVD), and the sp 2 carbon content was less than 5.56%. The nucleation and growth of diamond film were investigated by micro-Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. The results show that the nucleation density of diamond on the Ni-modified Cu substrates is 10 times higher than that on blank Cu substrates. The enhancement mechanism of the nucleation kinetics by Ni modification layer results from two effects: namely, the nanometer rough Ni-modified surface shows an improved absorption of nanodiamond particles that act as starting points for the diamond nucleation during HF-CVD process; the strong catalytic effect of the Ni-modified surface causes the formation of graphite

Improving the long-term stability of Ti6Al4V abutment screw by coating micro/nano-crystalline diamond films.

Abutment screw loosening is the most common complication of implanting teeth. Aimed at improving the long-term stability of them, well-adherent and homogeneous micro-crystalline diamond (MCD) and nano-crystalline diamond (NCD) were deposited on DIO(®) (Dong Seo, Korea) abutment screws using a hot filament chemical vapor deposition (HFCVD) system. Compared with bare DIO(®) screws, diamond coated ones showed higher post reverse toque values than the bare ones (p<0.05) after cyclic loading one million times under 100N, and no obvious flaking happened after loading test. Diamond coated disks showed lower friction coefficients of 0.15 and 0.18 in artificial saliva when countered with ZrO2 than that of bare Ti6Al4V disks of 0.40. Though higher cell apoptosis rate was observed on film coated disks, but no significant difference between MCD group and NCD group. And the cytotoxicity of diamond films was acceptable for the fact that the cell viability of them was still higher than 70% after cultured for 72h. It can be inferred that coating diamond films might be a promising modification method for Ti6Al4V abutment screws.

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi1/3Co1/3Mn1/3O2 thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi1/3Co1/3Mn1/3O2 (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200xa0cycles at 50xa0μAxa0μm−1xa0cm−2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1xa0μAhxa0μm−1xa0cm−2) compared with that of the NCM/AZO-120s electrode (62.4xa0μAhxa0μm−1xa0cm−2) and the bare NCM electrode (22.3xa0μAhxa0μm−1xa0cm−2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.

Highly Stable and Regenerative Graphene–Diamond Hybrid Electrochemical Biosensor for Fouling Target Dopamine Detection

Graphene is widely recognized as a promising nanomaterial for the construction of high-performance electrochemical biosensors. However, the lack of strong interfacial forces between graphene and conductive substrates is a bottleneck in the fabrication of highly stable graphene electrodes. In this work, few-layer graphene was directly formed on a high pressure high temperature (HPHT) diamond substrate via sp3-to-sp2 conversion by catalytic thermal treatment and using diamond itself as the carbon source. The hybrid electrode prototype was also highly conductive and had a linear electrochemical response to dopamine in the concentration range of 5u202fμM - 2u202fmM, with a low detection limit of 200u202fnM. After prolonged and repeated exposure to dopamine, electrode fouling was observed which led to sensitivity degradation. Based on the strong interfacial bonding between graphene and HPHT diamond, regeneration of the fouled electrode and full performance recovery would be easily achieved by ultrasonic cleaning. The hybrid electrode is highly robust, and shows potential in its application to the detection of biofouling molecules, food processing and wastewater treatment.

Growth mechanism of icosahedral and other five-fold symmetric diamond crystals

Abstract Five-fold symmetric diamond crystals (FSDCs) were synthesized by hot filament chemical vapour deposition (HFCVD) methods. Their surface morphologies and defects were characterised by scanning electron microscopy (SEM). From the perspective of nucleation-growth, a growth mechanism for icosahedral and other five-fold symmetric diamond crystals was discussed. Computer modelling was also carried out. The results show that the dodecahedrane (C 20 H 20 ) molecule is proposed as a nucleus for the growth of icosahedral diamond crystals (IDCs), wherein the 20 {111} surface planes develop orthogonal to the direction of the original 20… C…H bonds by sequential H abstraction and CH 3 addition reactions. IDC can be pictured as an assembly of isosceles tetrahedra, with each tetrahedron contributing a {111} plane to the surface of the IDC and the remainder of the tetrahedral surfaces forming twin planes with neighbouring tetrahedra. The small mismatch (1.44°) between the {111} surface dihedral angle of a perfect icosahedron and that of a twinned icosahedron reveals itself via twin planes in the IDC grain. The modelling suggests how the relief of strain induced by this distortion could lead to the formation of defects such as concave pentagonal cavities at vertices and grooves along the grain edges that accord well with those observed experimentally. Similar arguments based on growth from the hexacyclo pentadecane (C 15 H 20 ) nucleus can also account for the observed formation of star and rod shaped FSDCs, and some of their more obvious morphological defects.

Micro/nano hierarchical structured titanium treated by NH4OH/H2O2 for enhancing cell response

In this paper, two kinds of titanium surfaces with novel micro/nano hierarchical structures, namely Etched (E) surface and Sandblast and etched (SE) surface, were successfully fabricated by NH4OH and H2O2 mixture. And their cellular responses of MG63 were investigated compared with Sandblast and acid-etching (SLA) surface. Scanning electron microscope (SEM), Surface profiler, X-ray photoelectron spectroscopy (XPS), and Contact angle instrument were employed to assess the surface morphologies, roughness, chemistry and wettability respectively. Hierarchical structures with micro holes of 10–30 μm in diameter and nano pits of tens of nanometers in diameter formed on both E and SE surfaces. The size of micro holes is very close to osteoblast cell, which makes them wonderful beds for osteoblast. Moreover, these two kinds of surfaces possess similar roughness and superior hydrophilicity to SLA. Reactive oxygen species were detected on E and SE surface, and thus considerable antimicrobial performance and well fixation can be speculated on them. The cell experiments also demonstrated a boost in cell attachment, and that proliferation and osteogenic differentiation were achieved on them, especially on SE surface. The results indicate that the treatment of pure titanium with H2O2/NH4OH is an effective technique to improve the initial stability of implants and enhance the osseointegration, which may be a promising surface treatment to titanium implant.

Highly Sensitive and Selective Potassium Ion Detection Based on Graphene Hall Effect Biosensors

Potassium (K+) ion is an important biological substance in the human body and plays a critical role in the maintenance of transmembrane potential and hormone secretion. Several detection techniques, including fluorescent, electrochemical, and electrical methods, have been extensively investigated to selectively recognize K+ ions. In this work, a highly sensitive and selective biosensor based on single-layer graphene has been developed for K+ ion detection under Van der Pauw measurement configuration. With pre-immobilization of guanine-rich DNA on the graphene surface, the graphene devices exhibit a very low limit of detection (≈1 nM) with a dynamic range of 1 nM–10 μM and excellent K+ ion specificity against other alkali cations, such as Na+ ions. The origin of K+ ion selectivity can be attributed to the fact that the formation of guanine-quadruplexes from guanine-rich DNA has a strong affinity for capturing K+ ions. The graphene-based biosensors with improved sensing performance for K+ ion recognition can be applied to health monitoring and early disease diagnosis.