Preparation of boron-doped diamond nanowires and their application for sensitive electrochemical detection of tryptophan

The paper reports on the fabrication and electrochemical investigation of boron-doped diamond nanowires (BDD NWs) electrodes. The nanowires were obtained directly from highly doped polycrystalline diamond substrates using reactive ion etching (RIE) with oxygen plasma. The technique does not require any complicated processing steps such as mask deposition or template removal. The influence of the surface state on the electrochemical characteristics is discussed. The interface with the most favourable electrochemical response is investigated for the detection of tryptophan using differential pulse voltammetry. A detection limit of 5 × 10^?7 M was obtained on oxidized BDD NWs, as compared to 1 × 10^?5 M recorded on planar oxidized boron-doped diamond interfaces.     

Preparation of boron-doped semiconducting diamond films using BF3 and the electrochemical behavior of the semiconducting diamond electrodes

Boron-doped semiconducting diamond films were prepared using BF₃ by microwave plasma assisted chemical vapor deposition. B-doping was confirmed by SIMS and Raman spectroscopic measurements and the B-doping levels were estimated. Electrochemical behaviors of boron-doped diamond thin-film electrodes prepared using B₂H₆ and BF₃ were studied by measuring cyclic voltammograms for anodic oxidation of 1,4-difluorobenzene in the liquid electrolyte, neat Et₄NF·4HF. The results of the direct thermal interaction of elemental fluorine with hydrogenated and oxidized diamond surfaces are also presented.     

Preparation of thin polymer films with controlled drug release

Poly(N-isopropylacrylamide) (PAAm) is a thermal responsive polymer that undergoes a structural change in aqueous solution at its lower critical solution temperature (LCST). PAAm-modified silicon substrates were prepared and the effect of PAAm density on the thermal response of the modified surface was examined in terms of changes in the water contact angle as a basis for applying the structural change of the polymer to controlled drug release. Changes with temperature in the ability to load and release of the modified layer for drug were also examined using 2-acetoxybenzoic acid (aspirin) as a model drug. The amount of PAAm was found to greatly affect the thermal response and the ability to load and release of the modified layer for aspirin.     

Electrochemical oxidation of thiocyanates on boron-doped diamond electrode in alkaline solutions

Electrochemical oxidation of thiocyanates on a boron-doped diamond electrode in an alkaline medium was studied. An analysis of polarization curves demonstrated that the process of SCN oxidation occurs at water deposition potentials and is controlled by the mass transfer of the substrate to the electrode surface. It is shown that the oxidation efficiency of thiocyanates and the specific electric energy expenditure depend on the current density and on the method by which the process is performed. At a current density of 8 mA cm^?2, more than 90% of thiocyanates is oxidized to CNO, carbon dioxide, and nitrogen with a specific energy expenditure of 26.3 kW h kg^?1 SCN.     

Comparison of the hole mobility in undoped and boron-doped polycrystalline CVD diamond films

The drift mobility of nonequilibrium holes injected in undoped polycrystalline diamond films was determined, by a transit-time technique, as ca. 10⁻³ cm²/(V s). This hole mobility is three orders of magnitude lower than the “equilibrium” mobility in boron-doped diamond films [0.1–1 cm²/(V s)], determined from the films' dc conductivity. This difference is explained by the effect of a nonequilibrium charge carrier trapping during the carrier transport in polycrystalline diamond. Received: 3 December 1997 / Accepted: 9 April 1998     

Preparation of thin silica films with controlled thickness and tunable refractive index

Silica films with controlled thickness and refractive index have been formed by the sequential adsorption of a cationic polyelectrolyte and silica sols. The conditions used to prepare the sol were varied, and allowed films with refractive indices as low as 1.16 to be obtained. The sequential adsorption technique allows the thickness of these films to be controlled in increments of 5-10 nm, depending on the desired refractive index. Scanning electron microscopy revealed that a low packing density of constituent silica particles was responsible for the low indices of these films. The as-adsorbed films are thermally robust; calcination at 500 degrees C resulted in only very small decreases in film thickness (by < or =1.8%) and refractive index (to as low as 1.14). After calcination, the silica films remained hydrophilic and sorbed water vapor from the atmosphere. As a result, the refractive indices of these films increased with increasing relative humidity (RH). The dependence of the refractive index on RH was eliminated by treating the calcined films with trimethylchlorosilane.     

Carbon nanodots as peroxidase mimetics and their applications to glucose detection

Carbon nanodots (C-Dots) were found to possess intrinsic peroxidase-like activity, and could catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) by H(2)O(2) to produce a colour reaction. This offers a simple, sensitive and selective colorimetric method for glucose determination in serum.     

Preparation and properties of solid state selenite ion selective electrodes and their applications

A new selenite ion selective electrode using solid salts of Ag(2)Se and Cu(2)S has been developed. Detailed information is provided concerning the composition, working pH and conditioning of the electrode. The change of potential with concentration is found to be linear in the range of 10(-5)-10(-2) M, the slope of the linear portion is 28 mV/10-fold change in selenite concentration. The effect of other ions on selenite response is evaluated and selenium content of anodic slime is determined.     

Electrochemical degradation of buprofezin insecticide in aqueous solutions by anodic oxidation at boron-doped diamond electrode

Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-1,3,5-thiadiazinan-4-one) is identified as a commonly used chemical with satisfactory biological activities against sucking insect pests, but its disposal causes serious environmental problems. This pesticide was treated by an electrolysis system using a boron-doped diamond (BDD) as anode and platinum as cathode. A number of experiments were run on a laboratory scale and the results are presented. The chemical oxygen demand (COD) measurement during the processing permitted the evaluation of the kinetic of organic matter decay and the instantaneous current efficiency. Different operating conditions and factors affecting the treatment process including current density, conductive electrolyte, pH, concentration of buprofezin, and time of electrolysis were studied and optimized. The best obtained conditions for COD removal on the BDD anode to degrade buprofezin solutions (COD₀ = 1,200 mg L^?1) include operating at 60 mA cm^?2 and 25 ± 3 °C. The high efficiency of this technology can be explained in terms of the direct electrooxidation at the BDD surface and the oxidation carried out by hydroxyl radicals (OH^?) and other electro-generated oxidants (Cl^?, ClO^?).     

Preparation and characterization of sol-gel derived KTiOPO4 thin films for integrated optical applications

A sol gel route has been developed to produce stoichiometric, dense and crack free KTiOPO₄ (KTP) thin films which exhibit waveguiding. This method involved the deposition and pyrolysis of hydrolyzed solutions of K, Ti and P alkoxides on an appropriate substrate. The final ceramic film morphology is greatly dependent on the preparation chemistry, apparently as a result of the formation of polymetallic complexes. The solution chemistry, processing conditions and their influence on the final ceramic film microstructure will be discussed in detail.Optical properties such as indices of refraction and optical losses have been found to be dependent on the film microstructures. Deposition on different substrates has been undertaken to promote preferential orientation and thus to try to minimize the optical losses in the films. This correlation between the optical losses and microstructures will be discussed in detail.     

Mediator-free amperometric determination of glucose based on direct electron transfer between glucose oxidase and an oxidized boron-doped diamond electrode

A mediator-free glucose biosensor, termed a “third-generation biosensor,” was fabricated by immobilizing glucose oxidase (GOD) directly onto an oxidized boron-doped diamond (BDD) electrode. The surface of the oxidized BDD electrode possesses carboxyl groups (as shown by Raman spectra) which covalently cross-link with GOD through glutaraldehyde. Glucose was determined in the absence of a mediator used to transfer electrons between the electrode and enzyme. O₂ has no effect on the electron transfer. The effects of experimental variables (applied potential, pH and cross-link time) were investigated in order to optimize the analytical performance of the amperometric detection method. The resulting biosensor exhibited fast amperometric response (less than 5 s) to glucose. The biosensor provided a linear response to glucose over the range 6.67×10⁻⁵ to 2×10⁻³ mol/L, with a detection limit of 2.31×10⁻⁵ mol/L. The lifetime, reproducibility and measurement repeatability were evaluated and satisfactory results were obtained.     

Flow-injection determination of iodide ion in nuclear emergency tablets, using boron-doped diamond thin film electrode

The electrochemical determination of iodide was studied at boron-doped diamond thin film electrodes (BDD) using cyclic voltammetry (CV) and flow-injection (FI) analysis, with amperometric detection. Cyclic voltammetry of iodide was conducted in a phosphate buffer pH 5. Experiments were performed using glassy carbon (GC) electrode as a comparison. Well-defined oxidation waves of the quasi-reversible cyclic voltammograms were observed at both electrodes. Voltammetric signal-to-background ratios (S/B) were comparable. However, the GC electrode gives much greater in the background current as usual. The potential sweep rate dependence exhibited that the peak current of iodide oxidation at 1 mM varied linearly (r² = 0.998) with the square root of the scan rate, from 0.01 to 0.30 V s⁻¹. This result indicates that the reaction is a diffusion-controlled process with negligible adsorption on BDD surface, at this iodide concentration. Results of the flow-injection analysis show a highly reproducible amperometric response. The linear working range was observed up to 200 μM (r² = 0.999). The detection limit, as low as 0.01 μM (3σ of blank), was obtained. This method was successfully applied for quantification of iodide contents in nuclear emergency tablets.     

Fabrication and nanoindentation properties of TiN/NiTi thin films and their applications in electrochemical sensing

Nanocrystalline TiN/NiTi thin films have been grown on silicon substrate by dc magnetron sputtering to improve the corrosion and mechanical properties of NiTi based shape memory alloys without sacrificing the phase transformation effect. Interestingly, the preferential orientation of the TiN films was observed to change from (1 1 1) to (2 0 0) with change in nature of sputtering gas from 70% Ar + 30% N₂ to 100% N₂. In present study the influence of crystallographic orientation of TiN on mechanical and corrosion properties of TiN/NiTi thin films was investigated. TiN (2 0 0)/NiTi films were found to exhibit high hardness, high elastic modulus, and thereby better wear resistance as compared to pure NiTi and TiN (1 1 1)/NiTi films. Electrochemical test revealed that TiN coated NiTi film exhibits better corrosion resistance in 1 M NaCl solution as compared to uncoated NiTi film. The application of TiN/NiTi films in the electrochemical sensing of dopamine, which has a critical physiological importance in Parkinson's disease, has been demonstrated. A comparison of voltammetric response of dopamine at silicon based electrodes modified with different nanocrystalline coatings indicated that these films catalyze the oxidation of dopamine.     

A flow injection method for the analysis of tetracycline antibiotics in pharmaceutical formulations using electrochemical detection at anodized boron-doped diamond thin film electrode

A method using flow injection (FI) with amperometric detection at anodized boron-doped diamond (BDD) thin films has been developed and applied for the determination of tetracycline antibiotics (tetracycline, chlortetracycline, oxytetracycline and doxycycline). The electrochemical oxidation of the tetracycline antibiotics was studied at various carbon electrodes including glassy carbon (GC), as-deposited BDD and anodized BDD electrodes using cyclic voltammetry. The anodized BDD electrode exhibited well-defined irreversible cyclic voltammograms for the oxidation of tetracycline antibiotics with the highest current signals compared to the as-deposited BDD and glassy carbon electrodes. Low detection limit of 10 nM (signal-to-noise RATIO = 3) was achieved for each drug when using flow injection analysis with amperometric detection at anodized BDD electrodes. Linear calibrations were obtained from 0.1 to 50 mM for tetracycline and 0.5–50 mM for chlortetracycline, oxytetracycline and doxycycline. The proposed method has been successfully applied to determine the tetracycline antibiotics in some drug formulations. The results obtained in percent found (99.50–103.01%) were comparable to dose labeled.     

Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Cd-Te薄膜的制备及表征

Cd-Te是一种重要的光电材料,它的禁带宽度为1·45eV,光吸收系数很大,厚度1μm的薄膜足以吸收能量大于CdTe禁带宽度的光所具有能量的99%[1],因此它是一种十分理想的太阳电池材料。Cd-Te薄膜制备的方法有喷涂法、电沉积法、丝网印刷法、分子束外延法、化学气相沉积法、近空间升华     

The electrochemical oxidation of ammonia at boron-doped diamond electrodes exhibits analytically useful signals in aqueous solutions

Boron-doped diamond electrodes are shown to exhibit well-defined analytically useful voltammetric signals for the electrochemical oxidation of ammonia in aqueous solutions in comparison to commonly used carbon based electrode substrates. Proof-of-concept is shown for the construction of a miniature amperometric ammonia gas sensor utilising conductive boron-doped diamond.