Biomedical subjects

Ning Bao

Publications and source records attributed to Ning Bao.

10 recordsLinked to original sources

PubMed2005

Electroosmotic flow in poly(dimethylsiloxane) microchannels.

This paper reports on the study of electroosmotic flow (EOF) in poly(dimethylsiloxane) (PDMS) microchannels on the basis of indirect amperometric detection method. Gradual increase of EOF rate in freshly prepared PDMS microchannels was observed with the running buffer of phosphate buffer solution (PBS). With the same concentration (10 mM) of PBS containing different cations and the same pH value (7.0) and, the time of the stable EOF in PDMS microchannels under the applied separation voltage of 1000 V was 49.8 s (Li+ -PBS), 57.1 s (Na+ -PBS), 91 s (K+ -PBS), respectively. Meanwhile, the different adsorption of cations (Li+, Na+ and K+) on hydrophobic PDMS wall was observed through their separation in PDMS microchannels. Such experimental results demonstrated that the EOF in PDMS microchannels came from the cations and anions adsorbed on PDMS wall. This study would not only help us understand the surface state of PDMS, but also provide a useful guidance for establishing the effective surface modification methods in PDMS microchip CE.

Dimethylpolysiloxanes↗

PubMed2005

Simple method for the separation and detection of native amino acids and the identification of electroactive and non-electroactive analytes.

Detection of native amino acids was accomplished using a capillary electrophoresis (CE)-amperometric detection system, in which a single carbon fiber cylinder (CFC) working electrode instead of a carbon fiber disc (CFD) electrode was mounted in the end part of a poly(dimethylsiloxane) (PDMS)/glass hybrid microchannel. Similar to that using CFD working electrode, here, the electrochemical reduction reaction at the working electrode is also coupled from the separation high voltage system, the coupling degree is related to the in-channel length of the CFC. This property simplifies the fabrication procedure of the working electrode and also provides a convenient and sensitive means for the determination of non-electroactive ions by amperometry. The present detection mode is successfully used to electrochemically detect non-electroactive arginine (Arg), threonine (Thr), glutamic acid (Glu) and electroactive cysteine (Cys). Furthermore, by simply changing the detection potential, we can easily distinguish peak mobilities of electroactive amino acids from that of non-electroactive amino acids.

Amino Acids↗

PubMed2005

Fabrication of poly(dimethylsiloxane) microfluidic system based on masters directly printed with an office laser printer.

Applications of poly(dimethylsiloxane) (PDMS)-based microfluidic systems are more popular nowadays. Previous fabrication methods of the masters for PDMS microchannels require complicated steps and/or special device. In this paper, we demonstrated that the toner printed on the transparency film with the office laser printer (1200 dpi) can be used as the positive relief of the masters. The transparency film was printed in two steps in order to obtain the same printing quality for the crossed lines. With the laser-printed master, the depth of the fabricated PDMS microchannels was ca. 10 microm and the smallest width was ca. 60 microm. Surface characteristics of the PDMS/PDMS microchannels were performed with SEM. Their electrokinetic properties were investigated by the aids of the measurement of electroosmotic flow (EOF) and the Ohm's curve. Using the PDMS/PDMS microchip CE systems, electroactive biological molecules and non-electroactive inorganic ions were well separated, respectively. This simple approach could make it easy to carry out the studies of PDMS microfluidic systems in more general labs without special devices.

Dimethylpolysiloxanes↗

PubMed2005

In-channel indirect amperometric detection of nonelectroactive anions for electrophoresis on a poly(dimethylsiloxane) microchip.

In the present paper, we describe a microfluidics-based sensing system for nonelectroactive anions under negative separation electric field by mounting a single carbon fiber disk working electrode (WE) in the end part of a poly(dimethylsiloxane) microchannel. In contrast to work in a positive separation electric field described in our previous paper (Anal. Chem. 2004, 76, 6902-6907), here the electrochemical reduction reaction at the WE is not coupled with the separation high-voltage (HV) system, whereas the electrochemical oxidation reaction at the WE is coupled with the separation HV system. The electroactive indicator is the carbon fiber WE itself but not dissolved oxygen. This provides a convenient and sensitive means for the determination of nonelectroactive anions by amperometry. The influences of separation voltage, detection potential, and the distance between the WE and the separation channel outlet on the response of the detector have been investigated. The present detection mode is successfully used to electrochemically detect F-, Cl-, SO4(2-), CH3COO-, H2PO4-. Based on the preliminary results, a detection limit of 2 microM and a dynamic range up to three orders of magnitude for Cl- could be achieved.

Anions↗

PubMed2004

Electrochemical detection method for nonelectroactive and electroactive analytes in microchip electrophoresis.

In this work, we establish an indirect amperometric detection method via mounting a single carbon fiber disk working electrode in the end part of a microchannel. This in-channel configuration for microchip capillary electrophoresis brings about that the potential of the working electrode in the case of electrochemical reduction reaction is coupled by the separation electric field, while the potential of the working electrode in the case of electrochemical oxidation reaction is not coupled by the separation electric field. Such a special performance provides a convenient and sensitive approach for indirectly detecting nonelectroactive analytes that relies on amperometric response of dissolved oxygen in solution and directly detecting electroactive analytes based on their own amperometric response on the carbon fiber electrode. This method has shown its essential importance in the analysis of inorganic cations, biomolecules, and electroosmotic flow rates. Based on preliminary results, a detection limit of 1.0 microM for K(+) and Na(+) have been achieved.

Carbon↗

PubMed2004

Improvement of heat dissipation for polydimethylsiloxane microchip electrophoresis.

Effective removing of Joule heat in polymer-based microchip system is an important factor for high efficient separation because of lower heat conductivity of polymers than silica or glass. In this paper, a new kind of polydimethylsiloxane (PDMS) microchip electrophoresis system integrated with a laser-induced fluorescence detector has been successfully constructed on the basis of a commercial heat sink for computer CPU (central processor unit). Experimental results on separation current using high concentration running buffers demonstrated that heat dissipation of PDMS/PDMS microchip system was significantly improved. Furthermore, with this integrated system, theoretical plate number of fluorescein using 100 mM phosphate-buffered saline + 1 mM sodium dodecyl sulfate as running buffer was determined to be 2750 (for 2.5-cm separation channel, corresponding to 110,000/m). This high separation efficiency demonstrated that such heat sink-based polymer microchip system could be effectively applied for high-concentration buffers.

Buffers↗

PubMed2004

Electrochemical detector for microchip electrophoresis of poly(dimethylsiloxane) with a three-dimensional adjustor.

This paper presents an electrochemical detector for poly(dimethylsiloxane) (PDMS) microchip CE with a three-dimensional adjustor which makes it possible to accurately align a separate working electrode that can be easily fabricated in laboratory to the uncertain PDMS microchannel outlet. The substantial influence of the electrode-PDMS microchannel distance was investigated. The optimal electrode-outlet distance was found to be 10 microm for the PDMS microchannel with the width of 50 microm due to its relatively slow electroosmotic flow. Adrenaline and catechol were well separated, with a linear response range from 20 microM to 1 mM, and a detection limit of 2 microM for catechol, using carbon disk electrode (diameter of 300 microm). Furthermore, arginine and histidine can be well separated and detected directly in the PDMS microchannel using a Cu disk electrode (diameter of 150 microm).

Dimethylpolysiloxanes↗

PubMed2004

Separation of proteins on surface-modified poly(dimethylsiloxane) microfluidic devices.

Separation and detection of proteins have been realized on nonionic surfactant-modified poly(dimethylsiloxane) (PDMS) microfabricated devices with end-column amperometric detection. The hydrophobic PDMS channels are turned into hydrophilic ones after being modified with Brij35 and facilitate the separation of proteins. The coating can remarkably reduce the adsorption of large protein molecules and is stable in the range of pH 6-12. The detection of proteins in such channels needs less rinsing time and thus efficiency is raised. Even large molecules of proteins can also be detected with better reproducibility and enhanced plate numbers. The relative standard deviation (RSD) of the migration time for glucose oxidase (GOD) is 2.2% (n = 19). Separation of GOD and myoglobin has been developed in modified channels. Predominant operational variables, such as the coating conditions, the concentration of surfactant and buffer, are studied in detail.

Dimethylpolysiloxanes↗

PubMed2004

MicroRNA binding sites in Arabidopsis class III HD-ZIP mRNAs are required for methylation of the template chromosome.

Dominant mutations in the Arabidopsis PHABULOSA (PHB) and PHAVOLUTA (PHV) transcription factor genes cause transformation of abaxial to adaxial leaf fates by altering a microRNA complementary site present in processed PHB and PHV mRNAs but not in the corresponding genomic DNA. phb-1d mutants accumulate excess PHB transcript throughout the leaf primordium, indicating defective regulation of PHB transcript synthesis and/or stability. We show that PHB and PHV coding sequences are heavily methylated downstream of the microRNA complementary site in most wild-type plant cells and that methylation is reduced in phb-1d and phv-1d mutants. Decreased methylation is limited to the chromosome bearing the dominant mutant allele in phb-1d heterozygotes. Low levels of methylation are detected in wt PHB DNA isolated from undifferentiated tissues. These results suggest a model in which the microRNA interacts with nascent, newly processed PHB mRNA to alter chromatin of the corresponding PHB template DNA predominantly in differentiated cells.

Alleles↗

PubMed2002

A dynamically modified microfluidic poly(dimethylsiloxane) chip with electrochemical detection for biological analysis.

Separation and direct detection of amino acids, glucose and peptide in a 3.1 cm separation channel made of poly(dimethylsiloxane) (PDMS) with end-column amperometric detection at a copper microdisk electrode was developed. This system is the integration of a normal sized working electrode with electrochemical detection on a PDMS microfabricated device. The PDMS channels dynamically modified by 2-morpholinoethanesulfonic acid (MES) show less adsorption and more enhanced efficiency than that of unmodified ones when applied to separations of these biological molecules. The migration time is less than 100 s and the reproducibility of migration time is satisfactory with relative standard deviation (RSD) of 2.8% in 19 successive injections. The limits of detection of arginine (Arg), glucose, and methionine-glycine (Met-Gly) are estimated to be 2.0, 8.5, and 64.0 microM at S/N = 3, approximately 0.5-16.0 fmol, respectively. Variances influencing the separation efficiency and amperometric response, including injection, separation voltage, detection potential, or concentration of buffer and additive, are assessed and optimized.

Alkanesulfonic Acids↗