Microdevices for manipulation and accumulation of micro- and nanoparticles by dielectrophoresis

Microfluidic devices with three-dimensional (3-D) arrays of microelectrodes embedded in microchannels have been developed to study dielectrophoretic forces acting on synthetic micro- and nanoparticles. In particular, so-called deflector structures were used to separate particles according to their size and to enable accumulation of a fraction of interest into a small sample volume for further analysis. Particle velocity within the microchannels was measured by video microscopy and the hydrodynamic friction forces exerted on deflected particles were determined according to Stokes law. These results lead to an absolute measure of the dielectrophoretic forces and allowed for a quantitative test of the underlying theory. In summary, the influence of channel height, particle size, buffer composition, electric field, strength and frequency on the dielectrophoretic force and the effectiveness of dielectrophoretic deflection structures were determined. For this purpose, microfluidic devices have been developed comprising pairs of electrodes extending into fluid channels on both top and bottom side of the microfluidic channels. Electrodes were aligned under angles varying from 0 to 75 degrees with respect to the direction of flow. Devices with channel height varying between 5 and 50 microm were manufactured. Fabrication involved a dedicated bonding technology using a mask aligner and UV-curing adhesive. Particles with radius ranging from 250 nm to 12 microm were injected into the channels using aqueous buffer solutions.     

Application of an artificial neural network (ANN) and piezoelectric chemical sensor array for identification of volatile organic compounds

A piezoelectric chemical sensor array was developed using four quartz crystals. Gas chromatographic stationary phases were used as sensing materials and the array was connected to an artificial neural network (ANN). The application of the ANN method proved to be particularly advantageous if the measured property (mass, concentration, etc.) should not be connected exactly to the signal of the transducers of the piezoelectric sensor. The optimum structure of neural network was determined by a trial and error method. Different structures were tried with several neurons in the hidden layer and the total error was calculated. The optimum values of primary weight factors, learning rate (η=0.15), momentum term (μ=0.9), and the sigmoid parameter (β=1) were determined. Finally, three hidden neurons and 900 training cycles were applied. After the teaching process the network was used for identification of taught analytes (acetone, benzene, chloroform, pentane). Mixtures of organic compounds were also analysed and the ANN method proved to be a reliable way of differentiating the sensing materials and identifying the volatile compounds.     

A multiple coupling approach to produce high-performance SERS substrates

In this work, large area gold-nanoparticle-cluster pillar array with a gold mirror as high-performance SERS substrate was facilely fabricated by combined use of nanosphere lithography and self-assembly approach.     

Synthesis of mono meso-pyridyl 21,23-dithiaporphyrins and unsymmetrical non-covalent porphyrin dimers

A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single products in 8-11% yield. Two of the three mono meso-pyridyl N₂S₂ porphyrins were used to synthesize non-covalent unsymmetrical porphyrin dimers containing one N₂S₂ and one N₄ porphyrin cores.     

Analysis of Terbumeton and its Major Metabolites by SPE and DAD-HPLC in Soil Bulk Water

A rapid and inexpensive method for simultaneous quantification of terbumeton (TER), and its major potential metabolites (TED; terbumeton-desethyl, TOH; terbumeton-2-hydroxy and TID; terbumeton-deisopropyl) in soil bulk water (SBW) samples is proposed. The analytical method involves extraction–concentration from SBW samples using a graphitized carbon black (GCB) cartridge followed by their separation–detection by reversed-phase high-performance liquid chromatography analysis using a C₁₈ column and a diode array detector. A mobile phase of acetonitrile−0.005 mol L⁻¹ phosphate buffer (pH 7.0) (35:65, v/v) at a flow rate of 0.8 mL min⁻¹ in isocratic elution mode has been used. After optimization of the extraction and separation conditions, this method can be used for the simultaneous determination of investigated compounds in the range of the international limits of 0.1 μg L⁻¹. For TER the detection limit was 0.009 μg L⁻¹ and it was 0.100, 0.550, and 0.480 μg L⁻¹ for TED, TOH, and TID, respectively. The recoveries of TER, TED, TOH, and TID from SBW samples, measured at three levels of concentration range, were found to be between 48.0 and 102.0%. The intra-day precision measured by relative standard deviation (RSD) was always lower than 9.0%.     

Simplified Solid-Phase Extraction Procedure and Liquid Chromatographic Determination of Celecoxib in Rat Serum

A simplified solid phase extraction method, eliminating a preliminary protein precipitation has been developed for the determination of celecoxib in rat plasma. The technique included a solid phase extraction of the serum samples on a [poly (divinylbenzene-co-N-vinylpyrrolidone)] sorbent. After conditioning, the cartridge was loaded with 0.5 mL of acidified serum containing internal standard. Elution was made with 1 mL of a mixture of acetonitrile and methanol (1/1, v/v). After evaporation of the eluate to dryness and reconstitution with methanol, the samples were analyzed on an octadecyl bonded phase with several mobile phases containing acetonitrile and a phosphate buffer. Detection was carried out using a Photodiode Array Detector. Full validation of the proposed method was provided (linearity range: 0.01–2 mg. L^–1, average extraction efficiency: 92.4%; average intra-day variability: 4.6% with an accuracy of 94.8%; average interday variability: 5% with an accuracy of 95.3%, limit of detection: 0.005 mg. L^–1, limit of quantification: 0.002 mg. L^–1). The proposed method was successfully utilised to quantify celecoxib in rat plasma for a pharmacokinetic study.Revised: 26 January and 23 April 2004     

氨水溶液制备ZnO纳米晶阵列的研究

以氨水和硝酸锌为前躯体，采用低温水溶液法在涂敷ZnO晶种层的玻璃衬底上外延生长了ZnO纳米棒晶阵列。应用SEM、TEM、SAED和XRD表征了ZnO纳米晶的形貌和结构。讨论了该组成体系水溶液法纳米棒外延生长的机理及其对棒晶形貌的影响。通过对水溶液pH值的原位二次调整，制备出了ZnO纳米管和表面绒毛状的棒晶阵列，基于生长机理探讨了它们的形成原因，为实现不同形貌ZnO纳米晶阵列的优化控制提供了可能的技术途径。结果表明，不同形貌的ZnO均属沿c轴择优取向的六方纤锌矿结构。     

Trace Detection of Mercury(II) Using Gold Ultra‐Microelectrode Arrays

The electroanalytical detection of trace mercury(II) at gold ultra‐microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in nitric acid using linear sweep voltammetry where a linear response from mercury additions over the range 10 μg L^?1?200 μg L^?1 (10^?8?10^?6 M) was observed with a sensitivity and detection limit of 0.11 nC/μg L^?1 and 3.2 μg L^?1 (16 nM) respectively from using a deposition time of 30 s at ?0.2 V (vs. SCE). This methodology was explored in 0.1 and 1 M chloride media over the mercury range 10 μg L^?1?200 μg L^?1 (5×10^?8?10^?6 M) where similar sensitivities of 0.087 nC/μg L^?1 and 0.078 nC/μg L^?1 were observed with an identical detection limit. The protocol is demonstrated to be useful for the determination of mercury for analysis of environmental water samples.     

Determination of Enantiomeric Excess of Glutamic Acids by Lab-made Capillary Array Electrophoresis

The techniques of combinatorial chemistry have recently been applied to the discovery of new asymmetric catalyst for a variety of organic transformations1-3. Using combina- torial methods, it is straightforward to generate thousands of potential asymmetri…     

Hydrothermal Synthesis and Optical Properties of ZnO Nanostructured Films Directly Grown from/on Zinc Substrates

Uniform ZnO nanorods arrays are grown directly from and on Zn foils in pure water under hydrothermal conditions at a relatively low temperature. The nanorods are 80–200 nm in diameter and ∼ 1 μm in length, which grow on the Zn foil along the [001] direction. By changing the pure water to a urea solution, a Zn compound ([Zn₅(OH)₆(CO₃)₂], a precursor of ZnO nanoflowers film, is created by self-assembly. The ZnO nanoflowers film can be easily obtained by heating the [Zn₅(OH)₆(CO₃)₂] compound in N₂ at 350∘C for 5–6 hours. Possible growth processes of the ZnO nanorods arrays and the [Zn₅(OH)₆(CO₃)₂] nanoflowers are discussed. Photoluminescence properties of the as-prepared ZnO nanostructures have been measured. The ZnO nanorods array synthesized using our method has minimal defects so that only band-gap emission is observed. However, the ZnO nanoflowers film, obtained by heating the [Zn₅(OH)₆(CO₃)₂] nanoflower precursor in N₂, is polycrystalline and displays strong defect-related emission.