Biomedical subjects

Zhiwei Zhu

Publications and source records attributed to Zhiwei Zhu.

9 recordsLinked to original sources

PubMed2006

Fabrication and characterization of submicrometer- and nanometer-sized double-barrel pipets.

Submicro- and nanometer-sized glass double-barrel pipets have been fabricated by a laser puller with new pulling programs and have been used to support submicro- and nanometer dual liquid/liquid interfaces. The smallest pipet that can be made by this approach is approximately 20 nm in radius. These pipets have been characterized by cyclic voltammetry and scanning electron microscopy. Generation/collection mode of charge-transfer reaction is demonstrated at the submicro- and nanometer dual-liquid/liquid interfaces. The dependence of collection efficiency upon geometric parameters of the pipets has been discussed. Among the micro-, submicro-, and nanopipets, we have found that the submicro-double-barrel pipets have higher collection efficiencies than that of others and are also very close to the values predicted by the theory. Therefore, in terms of G/C mode applications, the optimal size of double-barrel pipets should be in submicrometer scale. As one of the examples of special application, we have also demonstrated that in the case of no supporting electrolyte, only the nanometer double-barrel pipets can provide reasonably good G/C results.

Journal Article↗

PubMed2006

Ferrocene peapod modified electrodes: preparation, characterization, and mediation of H2O2.

Electrochemical properties of a new nanomaterial ferrocene (Fc) peapod, Fc-filled single-walled carbon nanotubes (Fc@SWNTs), have been investigated in an aqueous solution in detail by preparing different kinds of Fc@SWNTs-modified glassy carbon electrodes (Fc@SWNTs/GCE and Fc@SWNTs-gel/GCE). One pair of surface-confined redox waves corresponding to the couple of Fc/Fc+ is obtained, which indicates that Fc encapsulated inside SWNTs retains electrochemical activity. The Fc@SWNTs-gel/GCE shows better electrochemical reversibility due to the existence of room temperature ionic liquid (RTIL). Furthermore, it shows excellent mediation of H2O2 based on Fc/Fc+ used as electron-transfer mediators for oxidation of H2O2 to O2 and reduction to H2O, suggesting specific properties of Fc@SWNTs due to a combination of Fc and SWNTs. The interaction between Fc and SWNTs is also characterized by UV-vis-NIR spectrometry and Raman spectrometry. A Fc@SWNTs-based sensor for H2O2 with a determination limit of 5 microM is fabricated, and it shows good stability and reproducibility. This work not only demonstrates that the Fc peapod is a new kind of functional nanomaterial but also appears promising in constructing novel chemical and biosensors and fuel cells.

Journal Article↗

PubMed2006

A novel electrochemical biosensor for the detection of uric acid and adenine.

A novel electrochemical biosensor for the detection of uric acid and adenine was prepared based on a gel containing multi-walled carbon nanotubes and room-temperature ionic liquid of 1-octyl-3-methylimidazolium hexafluorophosphate. The electrochemistry of uric acid and adenine was studied in this gel modified electrode. There was a significant two-way electrocatalytic activity upon both oxidation and reduction of uric acid. Similar to a bare glassy carbon electrode, uric acid undergoes a 2e,2H+ oxidation in phosphate buffer in the modified electrode. A diimine, the oxidation product of uric acid, was found to be an unstable intermediate, which was converted by a follow-up hydration reaction to an imine alcohol, with the reaction rate constant of 8.5 +/- 0.3 M(-1).s(-1) according to Nicholson's theory. Under optimum conditions, linear calibration graphs were obtained over the concentration range of 1.0 x 10(-7) M approximately 1.0 x 10(-5) M (uric acid) and 1.0 x 10(-5) M approximately 6.0 x 10(-4) M (adenine). Based on the signal-to-noise ratio of 3, the detection limits of the current technique was found to be as low as 9.0 x 10(-8) M (uric acid) and 2.0 x 10(-6) M (adenine), respectively. This novel biosensor was successfully applied for the assay of uric acid in human urine. Because of its good stability and long-term durability, such a gel modified electrode can provide a simple and easy approach for sensitive detection of uric acid and adenine.

Adenine↗

PubMed2006

[Effects of water stress during grain-filling period on rice grain yield and its quality under different nitrogen levels].

To examine the effects of nitrogen (N) supply and water stress on rice grain yield and its quality, a pot experiment was conducted at Yangzhou University. Three rice cultivars were grown under two N levels (high N and normal N) from initial heading, and two water conditions (well watering and water stress) were installed for each of the two N levels from flowering to maturity. The results showed that when the plants of test cultivars were grown under normal N level, water stress markedly reduced the grain-filling percentage and grain weight, resulting in a significant decrease of grain yield by 11.6% to approximately 14.7%. Though the head-milled rice had a slight increase, the percentage of chalkiness was significantly increased by 18.7% to approximately 33.1%, which resulted in an inferior performance in grain-apparent quality. In contrast, when the plants were grown under high N level, water stress increased the grain yield by 18. 8% to approximately 22.2% because of the increase of grain-filling percentage and grain weight. As compared with well watering, water stress decreased the percentages of chalky grain and chalkiness by 15.3% to approximately 37.2% and 13.7% to 29.9%, respectively, which improved the performance of grain-apparent quality. The pronounced effects of N application and water treatment were observed on the RVA profile and cooked quality. Under both two N levels, water stress decreased the peak viscosity and breakdown (except for Yangdao 6) while increased the setback. According to the performance in the indices of cooked quality, the palatability became poor when subjected to water stress under normal N level, as the result of the increase of hardness and cohesiveness. In contrast, under high N level, water stress availed the ascending of viscosity at the early stage when rice flours were pasting, peak viscosity and breakdown were increased, and setback was decreased, suggesting that the palpability got well. It was concluded that mild water stress during grain-filling period was benefit for the development of high quality grain when rice plants were grown under high N level.

Biomass↗

PubMed2005

Cadmium and lead contamination in japonica rice grains and its variation among the different locations in southeast China.

On the basis of a large-scale survey with 269 sampling sites and a field experiment with 12 cultivars grown at 3 ecologically different locations, Cadmium (Cd) and lead (Pb) contamination in milled rice grains and its variation among different locations were investigated in the area of southeast China. The objective of this study was mainly to assess the present situation of Cd and Pb contamination in rice grains harvested locally and find out the variation of Cd and Pb background levels in rice grains among the diverse regional locations. The results showed that: a) Cd concentrations in milled rice grains ranged from trace (below 10 ng/g) to 340 ng/g, with the means of 81.4 ng/g (AM) and 55.2 ng/g (GM) for the 269 samples, whereas Pb concentrations ranged from trace (below 10 ng/g) to 1136 ng/g, with the means of 113.5 ng/g (AM) and 51.0 ng/g (GM), respectively. High frequency was observed for both the Cd and Pb concentrations ranging from trace to 200 ng/g, with 95.9% for Cd and 84.8% for Pb, respectively. b) ANOVA for the AMs and GMs among 269 sampling sites indicated that there were significant differences among the different spatial locations in Cd or Pb concentrations. c) The Cd concentrations in milled rice grains were poorly correlated with Pb concentration among the 269 sampling sites surveyed, and no significant difference (P>0.05) in the AMs or GMs of Cd and Pb concentration was observed among different cities within a range of the same provinces, only with an exception for 1-2 provinces. d) Variance analysis of Cd, Pb concentrations for 12 rice cultivars grown in three locations showed that the great difference in coefficients of variation (CV) was observed both among cultivars grown in the same location and among locations of cultivars planted, in which locations showed much more contribution to the variation of Cd or Pb concentration in milled rice grains as compared with cultivars.

Cadmium↗

PubMed2005

Direct proteins electrochemistry based on ionic liquid mediated carbon nanotube modified glassy carbon electrode.

A novel glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes (MWNTs) and ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) is reported. The gel is formed by grinding of MWNTs and BMIPF6. Such gel is then coated on the surface of a glassy carbon electrode. We have employed scanning electron microscopy, Fourier transform infrared spectrometry (FTIR) and cyclic voltammetry to characterize the modified electrode. The direct electron transfers of hemoglobin and catalase on the modified electrode have been observed and studied in detail electrochemically. Hemoglobin is verified to be adsorbed on the modified electrode with the retention of conformation, which has been proved by microscopic FTIR. The electrochemical response of the adsorbed hemoglobin on the modified electrode is very stable, and shows repeated changes in the different pH solutions. It also has shown electrocatalysis to the reduction of oxygen and trichloroacetic acid. Catalase adsorbed on the gel modified electrode still keep activity to hydrogen peroxide. This work provides a simple and easy approach to construct biosensors based on the carbon nanotubes and ionic liquids.

Carbon↗

PubMed2004

Electrochemical investigation of dopamine at the water/1,2-dichloroethane interface.

Dopamine is an important neurotransmitter in mammalian central and peripheral nervous systems and is also a medicament to cure some neuropsychosis. In this work, ion transfer (IT), facilitated ion transfer (FIT) of protonated dopamine, and electron transfer (ET) between dopamine and ferrocene are investigated at the water/1,2-dichloroethane (W/DCE) interface. The IT and FIT reactions of protonated dopamine can be observed simultaneously within the same potential window. The experimental results demonstrate that dibenzo-18-crown-6, dibenzo-24-crown-8, and benzo-15-crown-5 work well with the protonated dopamine. The amperometric detection of dopamine based on either the IT or the FIT of protonated dopamine can get rid of the interference of ascorbic acid, and the lowest concentration that can be determined is approximately 0.05 microM by differential pulse voltammetry. For the ET reaction, its kinetics can be evaluated by scanning electrochemical microscopy, and the results show that the relationship between rate constants and driving force at the unmodified W/DCE interface obeys the Butler-Volmer equation in a rather wide potential region. When the W/DCE interface is modified by egg lecithin, the ET rate constants decrease with increasing concentration of egg lecithin, which indicates that egg lecithin hinders the ET reaction. When the driving force is increased to a certain degree, the linear relationship between ET rate constants and the driving force is distorted. These results will be helpful to understand both the pharmacodynamics and the neural signal transmission mechanism of dopamine at biological membranes and also provide a novel way to detect dopamine.

Dopamine↗

PubMed2003

Large-volume sample stacking combined with separation by 2-hydroxypropyl-beta-cyclodextrin for analysis of isoxyzolylpenicillins by capillary electrophoresis.

A simple, quick and sensitive capillary electrophoretic technique has been developed for the pharmaceutical analysis of isoxazolylpenicillins (oxacillin, cloxacillin and dicloxacillin) at trace levels for the first time. This method comprises large-volume sample stacking using the electroosmotic flow (EOF) pump (LVSEP), separation using 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as selective complex-forming background electrolyte additive, and direct UV detection. A complete resolution was achieved in the optimal background electrolyte containing 5.2 mM HP-beta-CD. LVSEP was successfully applied in their determinations to improve the sensitivity, where the EOF in the buffer zone was suppressed by using an acidic buffer with pH 3.6. The detection limits of the current technique were found to be 2.0 microg/L for each of the isoxazolylpenicillins based on the signal-to-noise ratio of 3. The curves of peak response versus concentration were linear from 5.0 to 400.0 microg/L with regression coefficients of 0.9982, 0.9986 and 0.9976, respectively. The interaction of isoxazolylpenicillins with HP-beta-CD was discussed. The association constants for complexes of HP-beta-CD with isoxazolylpenicillins were determined by electrophoretic method. The obtained association constants were 27.3, 34.9, and 48.5 M(-1), respectively, being proportional to their hydrophobic properties and steric hindrances. A simple and easy-manipulative sample preparation method was developed and validated by analyzing commercially available milk samples. It was found that with current sample preparation process and instrumentation system, 0.1 mL of milk sample is enough for the analysis of isoxazolylpenicillins to meet European Union (EU) guideline of 30 microg/kg.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2002

Large-volume sample stacking for analysis of ethylenediaminetetraacetic acid by capillary electrophoresis.

A simple, quick, and sensitive capillary electrophoretic technique-large volume stacking using the electroosmotic flow (EOF) pump (LVSEP) - has been developed for determining ethylenediaminetetraacetic acid (EDTA) in drinking water for the first time. It is based on a precapillary complexation of EDTA with Fe(III) ions, followed by large-volume sample stacking and direct UV detection at 258 nm. The curve of peak response versus concentration was linear from 5.0 to 600.0 microg/L, and 0.7 to 30.0 mg/L. The regression coefficients were 0.9988 and 0.9990, respectively. The detection limit of the current technique for EDTA analysis was 0.2 microg/L with an additional 10-fold preconcentration procedure, based on the signal-to-noise ratio of 3. As opposed to the classical capillary zone electrophoresis (CE) method, the detection limit was improved about 1000-fold by using this LVSEP method. To the best of our knowledge, it represents the highest sensitivity for EDTA analysis via CE. Several drinking water samples were tested by this novel method with satisfactory results.

Buffers↗