Electrophoresis (Electrophoresis)

Publications in this journal

• Article: Encapsulated Electrodes for Microchip Devices: Microarrays and Platinized Electrodes for Signal Enhancement.

  Asmira Selimovic, R Scott Martin
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  ABSTRACT: In this paper, we present two new methodologies of improving the performance of microchip-based electrochemical detection in microfluidic devices. The first part describes the fabrication and characterization of epoxy-embedded gold microelectrode arrays that are evenly spaced and easily modified. Electrodepositions using a gold plating solution can be performed on the electrodes to result in a 3-dimenional pillar array that, when used with microchip-based flow injection analysis, leads to an 8-fold increase in signal (when compared to a single electrode), with the limit of detection (LOD) for catechol being 4 nM. For detecting analytically challenging molecules such as nitric oxide (NO), platinization of electrodes is commonly used to increase the sensitivity. It is shown here that microchip devices containing either the pillar arrays or more traditional glassy carbon electrodes can be modified with platinum black for NO detection. In the case of using glassy carbon electrodes for NO detection, integration of the resulting platinized electrode with microchip-based flow analysis resulted in a 10 times signal increase relative to use of a bare glassy carbon electrode. In addition, it is demonstrated that these electrodes can be coated with Nafion to impart selectivity towards NO over interfering species such as nitrite. The LOD for NO when using the platinum black/Nafion-coated glassy carbon electrode was 9 nM. These electrodes can also be embedded in a polystyrene substrate, with the applicability of these sensitive and selective electrodes being demonstrated by monitoring the ATP-mediated release of NO from endothelial cells immobilized in a microfluidic network without any adhesion factor. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: An on-line sample preconcentration technique based on a dynamic pH junction in capillary electrophoresis-amperometric detection for the analysis of biogenic amines in urine.

  Wanrong Tang, Shuli Ge, Fan Gao, Guan Wang, Qingjiang Wang, Pingang He, Yuzhi Fang
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  ABSTRACT: It is difficult to detect biogenic amines in biological fluids because of their very low concentrations. In this paper, we reported an on-line sample preconcentration method in capillary electrophoresis-amperometric detection (CE-AD) based on a dynamic pH junction, and a concentration enhancement of approximately 100-fold was achieved compared with the classical CE-AD methods in the simultaneous analysis of six biogenic amines in urine (dopamine, epinephrine, norepinephrine, tyramine, tryptamine, and serotonin). The technique is proposed based on the sharp pH change generated at the boundary between an acidic sample and the basic background electrolyte (BGE) zone. Under optimised conditions, all analytes were successfully focused and well-separated within 20 min with high efficiency and sensitivity (LODs at S/N = 3 ranging from 5.34 to 68.3 nM). For the analysis of urine samples by this method, satisfactory recoveries were obtained without a complicated pretreatment step or derivatisation process. Therefore, it is self-evident that this approach for the analysis of real biological samples has great potential in the future. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: Pressurized capillary electrochromatography with amperometric detection using mixed-mode monolithic column for rapid analysis of chlorophenols and phenol.

  Lanxiang Lu, Yankai Chen, Xiaowei Yu, Xiangzong Wu, Fengxiang Tang, Xiaoping Wu
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  ABSTRACT: A simple analysis of chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) and phenol was accomplished by coupling a pressurized capillary electrochromatography (pCEC) with amperometric detection. Efficient and reproducible separation of these compounds was achieved within 9 min on a capillary monolithic stationary phase bonded with octadecyl ligands and sulfonate groups, where the selectivity and the retention of analytes can be functionally controlled by optimizing experimental variables, including organic modifier content, mobile phase pH, ionic strength, working electrode potential, separation voltage, and supplementary pressure. A mixed-mode retention mechanism consisting of reverse-phase chromatographic partition, electrostatic repulsion and electrophoresis is considered to play roles in the separation. The use of acetonitrile-based media seems effectual in preventing the unfavorable irreversible adsorption on both wall and electrode, and offer higher sensitivity and less electrode fouling in amperometric detection of phenols. The limits of detection were in the range from 0.02 to 0.2 μg mL(-1) with a wide linear dynamic range of 5000-fold, while the peak area precision ranged from 3.2% to 7.5%. The feasibility of using this method in real analysis was evaluated by recovery estimates and comparative experiment on spiked tap water samples. Good recoveries of 80-110% were achieved. Additionally, a paired t-test was used to correlate the two methods. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: A Gold-Gold Oil-Micro-Trench Electrode for Liquid-Liquid Anion Transfer Voltammetry.

  Sara E C Dale, Yohan Chan, Philip C Bulman Page, Edward O Barnes, Richard G Compton, Frank Marken
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  ABSTRACT: Two flat gold electrodes are placed vis-à-vis with an epoxy spacer layer that is etched out to give a ca. 100 μm deep electrochemically active trench. A water-insoluble oil phase, here the redox system N,N-diethyl-N'N'-didodecyl-phenylenediamine (DDPD) in 4-(3-phenylpropyl)-pyridine (PPP), is immobilised into the trench to allow anion transfer upon oxidation of DDPD(oil) to DDPD(+) (oil). In "mono-potentiostatic mode" quantitative transfer/expulsion of anions into the trench oil phase occurs. However, in "bi-potentiostatic mode" feedback currents dominated by rapid plate-to-plate diffusion normal to the electrode surfaces are observed. Comparison of "normal" diffusion and "lateral" diffusion shows that the rate of diffusion-migration charge transport across the oil film is anion hydrophobicity dependent. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: Nanostructured CaCO3 -PEI microparticles for phenol sensing in fluidic microsystem.

  Carmen C Mayorga-Martinez, Lenka Hlavata, Sandrine Miserere, Adaris López-Marzo, Jan Labuda, Josefina Pons, Arben Merkoçi
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  ABSTRACT: A new and simple strategy based on nanostructured CaCO3 -PEI MPs for phenol sensing using PDMS/glass fluidic microchip is developed. This fluidic microsystem including integrated screen-printed-electrodes (SPE) modified with CaCO3 -PEI MPs and tyrosinase (Tyr) through cross-linking with glutaraldehyde, represents a low cost platform for phenol detection. The designed fluidic microsystem improves the sensitivity of the biosensor allowing the detection of very low concentrations of phenol (up to 10 nM). This device shows high repeatability and low detection limit, is easy to be fabricated, inexpensive, disposable and amenable to mass production. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: Integration of a Graphite/PMMA Composite Electrode into a Poly(methyl methacrylate) (PMMA) Substrate for Electrochemical Detection in Microchips.

  Anne Regel, Susan Lunte
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  ABSTRACT: Traditional fabrication methods for polymer microchips, the bonding of two substrates together to form the microchip, can make the integration of carbon electrodes difficult. We have developed a simple and inexpensive method to integrate graphite/PMMA composite electrodes (GPCEs) into a PMMA substrate. These substrates can be bonded to other PMMA layers using a solvent-assisted thermal bonding method. The optimal composition of the GPCEs for electrochemical detection was determined using cyclic voltammetry with dopamine as a test analyte. Using the optimized GPCEs in an all-PMMA flow cell with flow injection analysis, it was possible to detect 50 nM dopamine under the best conditions. These electrodes were also evaluated for the detection of dopamine and catechol following separation by microchip electrophoresis (ME). This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: glyXalign: high-throughput migration time alignment pre-processing of electrophoretic data retrieved via xCGE-LIF-based glycoprofiling.

  Alexander Behne, Thilo Muth, Matthias Borowiak, Udo Reichl, Erdmann Rapp
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  ABSTRACT: Glycomics has become a rapidly emerging field and monitoring of protein glycosylation is needed to ensure quality and consistency during production processes of biologicals such as therapeutic antibodies or vaccines. Glycoanalysis via multiplexed capillary gel electrophoresis with laser-induced fluorescence detection (xCGE-LIF) represents a powerful technique featuring high resolution, high sensitivity as well as high-throughput performance. However, sample data retrieved from this method exhibit challenges for downstream computational analysis due to inter-sample migration time shifts as well as stretching and compression of electropherograms. Here, we present glyXalign, a freely available and easy-to-use software package to automatically correct for distortions in xCGE-LIF-based glyco-data. We demonstrate its ability to outperform conventional algorithms such as DTW and COW in terms of processing time and alignment accuracy for high-resolution datasets. Built upon a set of rapid algorithms the tool includes an intuitive graphical user interface and allows full control over all parameters. Additionally, it visualizes the alignment process and enables the user to re-adjust misaligned results. Software and documentation are available at http://www.glyxera.com. This article is protected by copyright. All rights reserved.
  Electrophoresis 05/2013;
• Article: Twenty-one years of microemulsion electrokinetic chromatography (1991-2012): A powerful analytical tool.

  Hua Yang, Yao Ding, Jun Cao, Ping Li
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  ABSTRACT: Electrophoresis 2013, 34, 1273-1294. DOI: 10.1002/elps.201200494 A powerful method to improve the resolution in MEEKC is the use of additives to the background electrolyte. Migration behaviors of analytes can be easily modified by additives, such as carbon nanotubes, ionic liquids, organic solvents and cyclodextrins. These additives can affect the interaction between microemulsions and analytes.
  Electrophoresis 05/2013; 34(9-10):NA.
• Article: Mapping AC Electroosmotic Flow at the Dielectrophoresis Crossover Frequency of a Colloidal Probe.

  Jingyu Wang, Ming-Tzo Wei, Joel A Cohen, H Daniel Ou-Yang
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  ABSTRACT: AC electroosmotic (ACEO) flow above the gap between coplanar electrodes is mapped by the measurement of Stokes forces on an optically-trapped polystyrene colloidal particle. E(2) -dependent forces on the probe particle are selected by amplitude modulation (AM) of the ACEO electric field (E) and lock-in detection at twice the AM frequency. E(2) -dependent dielectrophoresis (DEP) of the probe is eliminated by driving the ACEO at the probe's DEP crossover frequency. The location-independent DEP crossover frequency is determined, in a separate experiment, as the limiting frequency of zero horizontal force as the probe is moved toward the midpoint between the electrodes. The ACEO velocity field, uncoupled from probe DEP effects, was mapped in the region 1-9 μm above a 28 μm gap between the electrodes. By use of variously-sized probes, each at its DEP crossover frequency, the frequency dependence of the ACEO flow was determined at a point 3 μm above the electrode gap and 4 μm from an electrode tip. At this location the ACEO flow was maximal at ∼117 kHz for a low-salt solution. This optical trapping method, by eliminating DEP forces on the probe, provides unambiguous mapping of the ACEO velocity field. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Microfluidic biofunctionalisation protocols to form multivalent interactions for cell rolling and phenotype modification investigations.

  Gerardo Perozziello, Giuseppina Simone, Natalia Malara, Rosanna La Rocca, Rossana Tallerico, Rossella Catalano, Francesca Pardeo, Patrizio Candeloro, Giovanni Cuda, Ennio Carbone, Enzo Di Fabrizio
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  ABSTRACT: In this study we propose a fast, simple method to biofunctionalise microfluidic systems for cellomic investigations based on microfluidic protocols. Many available processes either require expensive and time-consuming protocols or are incompatible with the fabrication of microfluidic systems. Our method differs from the existing since it is applicable to an assembled system, uses few microliters of reagents and it is based on the use of microbeads. The microbeads have specific surface moieties to link the biomolecules and couple cell receptors. Furthermore, the microbeads serve as arm spacer and offer the benefit of the multivalent interaction. Microfluidics was adapted together with topology and biochemistry surface modifications to offer the microenvironment for cellomic studies. Based on this principle, we exploit the streptavidin-biotin interaction to couple antibodies to the biofunctionalised microfluidic environment within five hours using 200 μl of reagents and biomolecules. We selected the antibodies able to form complexes with the MHC class I (MHC-I) molecules present on the cell membrane and involved in the immune surveillance. To test the microfluidic system, tumour cell lines (RMAs) were rolled across the coupled antibodies to recognise and strip MHC-I molecules. As result, we show that cell rolling performed inside a microfluidic chamber functionalized with beads and the opportune antibody facilitate the removal of MHC class I molecules. We showed that the level of median fluorescent intensity (MFI) of the MHC-I molecules is 300 for cells treated in a not biofunctionalised surface. It decreased to 275 for cells treated in a flat biofunctionalised surface and to 250 for cells treated on a surface where biofunctionalised microbeads were immobilized. The cells with reduced expression of MHC-I molecules showed after cytotoxicity tests an NK susceptibility 3.5 times higher than normal cells. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Characterization of microchip electrophoresis devices fabricated by direct-printing process with colored toner

  E. F. M. GABRIEL, C. L. LAGO, A. L. GOBBI, E. CARRILHO, W. K. T. COLTRO
  Electrophoresis 04/2013;
• Article: Capillary electrophoresis as a production tool for asymmetric microhybrids.

  Zahra Fattah, Patrick Garrigue, Bertrand Goudeau, Véronique Lapeyre, Alexander Kuhn, Laurent Bouffier
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  ABSTRACT: The site selective electrodeposition of silver metal onto a conducting object such as carbon microtubes (CMTs) in an electrolytic solution could be achieved by means of bipolar electrochemistry (BPE). Two half-reactions are simultaneously carried out at both extremities of the CMT which act as a bipolar electrode. The thermodynamic threshold value of the process which consists in metal electro-reduction and concomitant water oxidation is directly related to the length of CMT. That is the reason why, when scaling down the methodology to microscale objects, electric fields in the range of tenths of kilovolts per meter are necessary. In that context, a capillary electrophoresis (CE) apparatus provides a convenient experimental platform to achieve in a straightforward manner such experimental conditions. We exemplify this methodology with the efficient and quick electro-reduction of Ag(+) on CMTs from a low-concentration aqueous electrolytic solution during the migration across a fused capillary. CE allows applying safely a large enough electric field (typically ∼ 30 kV/m) for the successful modification of 15 to 20 μm-long substrates. The corresponding hybrid materials have been characterized by optical microscopy as well as scanning electronic microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Preparation of chitosan-graft-(β-cyclodextrin) based sol-gel stationary phase for open-tubular capillary electrochromatography.

  Haixia Lü, Qingyin Li, Xiaowei Yu, Jiaojiao Yi, Zenghong Xie
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  ABSTRACT: A novel open-tubular capillary electrochromatography (OT-CEC) column coated with chitosan-graft-(β-cyclodextrin) (CDCS) was prepared using sol-gel technique. In the sol-gel approach, owing to the three-dimensional network of sol-gel and the strong chemical bond between the stationary phase and the surface of capillary columns, good chromatographic characteristics and unique selectivity in separating isomers were shown. The column efficiencies of 55 000∼163 000 plates/m for the isomeric xanthopterin and phenoxy acid herbicides using the sol-gel-derived CDCS columns were achieved. Good stabilities were demonstrated that the RSD values for the retention time of thiourea and isoxanthopterin were 1.3% and 1.4% (n = 5), 1.6% and 2.0% (n = 3), 2.9% and 3.1% (n = 3), respectively. The sol-gel-coated CDCS columns have shown improved separations of isomeric xanthopterin in comparison with CDCS-bonded capillary column. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Capillary electrophoresis with capacitively coupled contactless conductivity detection applied to the quantitation and to the determination of physical-chemical properties of peroxycarboxylates in aqueous medium.

  Denis Tadeu Rajh Vidal, Claudimir Lucio do Lago
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  ABSTRACT: Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4) D) was successfully applied to the investigation of performate, peracetate, and perpropionate in aqueous medium. Ionic mobilities, diffusion coefficients, and hydrodynamic radii were obtained for the first time for these species. CE-C(4) D was also used to estimate the pKa values of the peroxycarboxylic acids. Because the peroxycarboxylates (POCs) undergoes hydrolysis while migrating, a simple calibration curve cannot be used for quantitation. Thus, an indirect calibration approach was used. The new method was used to monitor the formation of peroxycarboxylic acids from hydrogen peroxide and the carboxylic acid as well as to the quantitation of peracetic acid in a commercial sample. The CE-C(4) D method compares favorably with the conventional titration method because of the possibility of speciation of the POC, the low sample consumption, and the low LOD (14, 8, and 24 μmol/L for performate, peracetate, and perpropionate, respectively). Although POCs are structural isomers of monoalkyl carbonates (MACs), they have greater hydrodynamic radii, which suggests that the positions of the oxygen atoms in the molecules have a direct impact in the charge density and consequently on the hydration atmosphere. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Determination of glyphosate and AMPA on polyester-toner electrophoresis microchip with contactless conductivity detection.

  Eduardo Rodrigues da Silva, Thiago Pinotti Segato, Wendell Karlos Tomazelli Coltro, Renato Sousa Lima, Emanuel Carrilho, Luiz Henrique Mazo
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  ABSTRACT: This paper reports a method for rapid, simple, direct, and reproducible determination of glyphosate and its major metabolite aminomethylphosphonic acid (AMPA). The platform described herein uses polyester-toner (PT) microchips incorporating capacitively coupled contactless conductivity detection (C(4) D) and electrophoresis separation of the analytes. The PT microchip presented 150-μm-wide and 12-μm-deep microchannels, with injection and separation lengths of 10- and 40-mm long, respectively. The best results were obtained with 320 kHz frequency, 4.5 Vpp excitation voltage, 80 mmol L(-1) CHES/Tris buffer at pH 8.8, injection in -1.0 kV for 7 s, and separation in -1.5 kV. RSD values related to the peak areas for glyphosate and AMPA were 1.5 and 3.3% and 10.1 and 8.6% for intra- and inter-chip assays, respectively. The detection limits were 45.1 and 70.5 μmol L(-1) , respectively, without any attempt of preconcentration of the analytes. Finally, the method was applied to river water samples in which glyphosate and AMPA (1.0 mmol L(-1) each) were added. The recovery results were 87.4% and 83.7% for glyphosate and AMPA, respectively. The recovery percentages and LOD values obtained here were similar to others reported in the literature. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: SU-8/Pyrex microchip electrophoresis with integrated electrochemical detection for class-selective electrochemical index determination of phenolic compounds in complex samples.

  Raquel Castañeda, Diana Vilela, María Cristina González, Sandra Mendoza, Alberto Escarpa
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  ABSTRACT: A SU-8/Pyrex single-channel microchip integrating three 100 μm Pt electrodes (ME-ED) for class-selective electrochemical index determination (CSEID) of phenolic acids and flavonoids in complex extracts of Tagetes lucida (Tl), Mentha piperita (Mp), Cymbopogon citratus (Cc), Calendula officinalis (Co) and Cynara scolymus (Cs) is proposed. Under strategic conditions controlled by a MES buffer (pH 5.0; 25mM) and accordingly to the antioxidant acid-base properties, the simultaneous measurement of total acids and flavonoids indexes was achieved in less than 100s with excellent analytical performance. The reliability of ME-ED approach was demonstrated towards the high agreement between the total phenolic content obtained using microchip approach with those obtained by the well-established HPLC-DAD; revealing both identical order regarding to the total phenolic content in the target samples. In addition, further comparison of ME-ED with the traditional Folin-Ciocalteu (FC) antioxidant capacity assay, showed that ME-ED approach could become a class-selective antioxidant capacity assay revealing that the sample antioxidant capacity was decreasing as Tl>Mp>Cs>Cc>Co according to their endogenous polyphenol content. These results suggested that the microchip approach is not only a reliable method for fast assessment of class-selective antioxidants constituting a very good alternative to the long analysis times and the using of toxic solvents required in HPLC but a novel truly antioxidant capacity assay. This excellent analytical performance is connected with the key-features of the "ready-to-use" system employed in this work such as portability, full integration of electrochemical detection, easy-operation and potential ME-ED disposability. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Spectroscopic and electrochemical characterization of nanostructured optically-transparent carbon electrodes.

  Tomas E Benavidez, Carlos D Garcia
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  ABSTRACT: The present paper describes the results related to the optical and electrochemical characterization of thin carbon films fabricated by spin coating and pyrolysis of AZ P4330-RS photoresist. The goal of this paper is to provide comprehensive information allowing for the rational the selection of the conditions to fabricate optically-transparent carbon electrodes (OTCE) with specific electro-optical properties. According to our results, these electrodes could be appropriate choices as electrochemical transducers to monitor electrophoretic separations. At the core of this manuscript is the development and critical evaluation of a new optical model to calculate the thickness of the OTCE by variable angle spectroscopic ellipsometry (VASE). Such data was complemented with topography and roughness (obtained by AFM), electrochemical properties (obtained by cyclic voltammetry), electrical properties (obtained by electrochemical impedance spectroscopy), and structural composition (obtained by Raman spectroscopy). Although the described OTCE were used as substrates to investigate the effect of electrode potential on the real-time adsorption of proteins by ellipsometry, these results could enable the development of other biosensors that can be then integrated into various CE platforms. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: "Stain-omics": Identification of mitotracker labeled proteins in mammalian cells.

  Hongjuan Dong, Sau Ha Cheung, Yimin Liang, Baojiang Wang, Rajkumar Ramalingam, Ping Wang, Hongyan Sun, Shuk Han Cheng, Yun Wah Lam
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  ABSTRACT: Organelle-specific cell-permeable fluorescent dyes are invaluable tools in cell biology as they reveal intracellular dynamics in living cells. Mitrotracker is a family of dyes that strongly label the mitochondrion, a key organelle associated with many crucial cellular functions. Despite the popularity of these dyes, little is known about the molecular mechanism behind their staining specificity. Here, we aimed to identify the protein targets of one member of this dye family, Mitotracker Red (MTR), by 2DE and MS. MTR bound to cellular proteins covalently, and its fluorescence persisted even after cell lysis, protein solubilisation, denaturation and electrophoresis. This enabled us to display MTR-labeled proteins by 2DE. The MTR-specific fluorescent signals on the gel revealed the spots that contained MTR-conjugated proteins. These spots were analysed by MS, resulting into the identification of 10 proteins. We discovered that one major target is the mitochondrial protein HSP60 and that MTR staining could induce production of HSP60, predisposing cells to heat shock-like responses. The identification of the molecular targets of biological dyes, or "stainomics", can help correlate their intracellular staining properties with biochemical affinities. We believe this approach can be applied to a wide range of fluorescent probes. This article is protected by copyright. All rights reserved.
  Electrophoresis 04/2013;
• Article: Evaluation of the enantioselectivity of carbon nanoparticles modified chiral separation systems using dextrin as chiral selector by capillary EKC.

  Xiaoyi Hua, Yingxiang Du, Jiaquan Chen, Guangfu Xu, Tao Yu, Qi Zhang
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  ABSTRACT: Nanoparticles (NPs) can be used as pseudostationary phases (PSPs) in electrokinetic chromatography (EKC), which is similar to the use of micelle additives as applied in micellar electrokinetic chromatography (MEKC). To date, the use of NPs to enhance enantiomeric separation by EKC with β-CD or its derivative as chiral selector has been reported only in two papers. However, to the best of our knowledge, there has been no prior effort to use NPs for achieving enantioseparation with polysaccharides as chiral selector. This paper describes for the first time the use of carbon nanoparticles (CNPs) as PSPs to modify chiral separation system employing dextrin as chiral selector for the enantioseparations of several basic drugs in capillary EKC. Three different types of CNPs, including carbogenic nanoparticles (NPs), carboxylated single-walled carbon nanotubes (c-SWCNTs) and carboxylated multi-walled carbon nanotubes (c-MWCNTs), were used as running buffer additives, respectively. The potential of the PSPs and the effects of dextrin concentration, buffer pH and buffer concentration on the enantioseparations were evaluated. Four pairs of tested enantiomers were successfully resolved in less than 15 min with the resolution values in the range of 1.41-4.52 under optimized conditions. Compared to the buffer without NPs, the introduction of NPs into the buffer enhanced the separation of the enantiomers.
  Electrophoresis 04/2013;
• Article: Evanescent-wave particle velocimetry measurements of zeta-potentials in fused-silica microchannels.

  Necmettin Cevheri, Minami Yoda
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  ABSTRACT: The wall ζ-potential ζw , the potential at the shear plane of the electric double layer, depends on the properties of the BGE solution such as the valence and type of electrolyte, the pH and the ionic strength. Most of the methods estimate ζw from measurements of the EOF velocity magnitude ueo , usually spatially averaged over the entire capillary. In these initial studies, evanescent-wave particle velocimetry was used to measure ueo in steady EOF for a variety of monovalent aqueous solutions to evaluate the effect of small amounts of divalent cations, as well as the pH and ionic strength of BGE solutions. In brief, the magnitude of the EOF velocity of NaCl-NaOH and borate buffer-NaOH solutions was estimated from the measured velocities of radius a = 104 nm fluorescent polystyrene particles in 33 μm fused-silica microchannels. The particle ζ-potentials were measured separately using laser-Doppler microelectrophoresis; ζw was then determined from ueo . The results suggest that evanescent-wave particle velocimetry can be used to estimate ζw for a variety of BGE solutions, and that it can be used in the future to estimate local wall ζ-potential, and hence spatial variations in ζw.
  Electrophoresis 04/2013;