Fabrication of a novel poly(dimethylsiloxane) microchips with two sharpened stretching tips

An integrated poly(dimethylsiloxane) (PDMS) microchip with two sharpened stretching has been presented. The sample was directly introduced into the separation channel through the stretching inlet tip without complicated power switching supplies and without injection cross-channel. Operations of running buffer refreshing or channel cleaning also becomes simple by vacuumed in one end and placed another tip into solution vial. The fabrication method can be easily applied in most analytical laboratories at low cost in the absence of soft lithography and plasma bonding equipments. Characteristics of the chips were tested and it can be used to separate fluorescence labeled molecules.     

MORPHOLOGICAL STUDIES OF PET FILMS WITH DIFFERENT CRYSTALLIZATION RATE IN DRAWING PROCESSES

Morphological changes during stretching of two PET samples (S and T) with different crystallization rate have been studied by means of SALS, solvent etching and polarizing microscope techniques. Results show that under the same drawing conditions larger and more perfect rod-like and spherulitic superstructures were formed more easily in the sample with higher crystallization rate (sample S). The amount of less compact regions which may be easily attacked by the vapor of allyl amine decreases more rapidly in sample S than in sample T during stretching, and these regions are more randomly distributed in sample T especially at low elongations. The difference of the two samples in morphological changes is coincident with their difference in tensile behavior.     

Construction of HIV-1 Virus-like Particle Vaccine

The virus-like particle（VLPs） vaccine is an ideal HIV-1 vaccine, which can simultaneously induce a neutralizing antibody reaction and cell-mediated immunity effectively. In this study, two kinds of plasmids have been used, one can express the HIV-1 main structure proteins, Gagpol and Env, and the other contains an antibiotic gene. The two kinds of plasmids have been cotransfected into 293 cells. A stable cell line that can express Gagpol and Env proteins efficiently and lastingly has been screened. It has been confirmed that Gagpol and Env proteins in the cell culture supernatant can be self-assembled into virus-like particles. The authors have detected the secretion of VLPs in the cell medium, defined the peak of the secretion, and followed and monitored the stability of expression.     

Determination of phenolic whitening agents in cosmetics by micellar electrokinetic capillary chromatography with amperometric detection

A sensitive method for simultaneous determination of six phenolic whitening agents,including arbutin, phenol,resorcinol,hydroquinone,kojic acid,and salicylic acid in cosmetics has been developed using micellar electrokinetic capillary chromatography with amperometric detection（MECC-AD）.Effects of several factors,such as the pH value and concentration of running buffer,potential applied to the working electrode,separation voltage,and injection time were investigated to obtain optimum conditions for separation and detection.With a 75 cm long fused-silica capillary tube,well-defined separation of six phenolic compounds was achieved in 10mmol/L SDS/40 mmol/L H₃BO₃-Na₂B₄O₇ running buffer（pH 9.0）.Good linear relationship was obtained for each analyte over three orders of magnitude with correlation coefficients（r2） between 0.9985 and 0.9994,and the detection limit（S/N=3） ranged from 0.04μg/mL to 0.45μg/mL The proposed method has been successfully applied for the determination of phenolic whitening agents in real cosmetic samples with satisfactory results,providing an alternative monitoring method for cosmetics safety regulation.     

A Novel Ionic Liquid／water Biphasic System for the Preparation of Oximes

A variety of carbonyl compounds can be converted into oximes efficiently and conveniently in a novel ionic liquid/water bi-phasic system in the presence of sodium bicarbonate at ambient temperature. The ionic liquid 1-butyl-3-methyl imidazolium hexafluorophosphate [bmim]PF6 is immiscible with water or diethyl ether and can be easily recycled for reuse without noticeable droping in activity after separation of the products. The protocol is rapid, the yields are excellent, the method is simple and the ionic liquid can be reused.     

Enhancement of Formation of Polar Microenvironment in Polymer by Compressed CO_2

To date, polar microenvironments in apolar solvents have been successfully used in different ways, such as separation of proteins1, enzymatic or catalytic reactions in reverse micelles2. It is obvious that investigation of new method to create polar microenvironments is of great importance to both pure and applied sciences, and it is desirable that forming and breaking the microenvironments can be easily controlled. Compressed CO2 can dissolve in many organic solvents and the solubility can …     

Study on Rhizoma Chuanxiong based on capillary electrophoresis with amperometric detection

<正>A high-performance capillary electrophoresis with amperometric detection(CE-AD) method has been developed for the analysis of seven bioactive ingredients,namely ferulic acid(FA),vanillin,vanillic acid,p-hydroxybenzoic acid,caffeic acid,gallic acid and protocatechuic acid,in Rhizoma Chuanxiong.The effects of several factors such as the acidity and concentration of running buffer,the separation voltage,the applied potential to working electrode and the injection time were investigated.Under the optimum conditions,the seven analytes could be well separated within 21 min at the separation voltage of 16 kV in a 60 mmol/L borax running buffer(pH 8.7).A 300μm diameter carbon disk electrode has a good response at potential of +950 mV(vs.SCE) for all analytes.Good linear relationship was established over three orders of magnitude with detection limits(S/N = 3) ranged from 3.3×10~(-7) to 6.7×10~(-9)g/mL.This proposed method has been successfully applied for the determination and comparison of different batches of Rhizoma Chuanxiong samples based on their characteristic electrochemical profiles.     

Simultaneous determination of active ingredients in blueberry wine by CE-AD

A method based on capillary electrophoresis coupled with amperometric detection（CE-AD） has been developed for the separation and determination of kaempferol,ferulic acid,vanillic acid,caffeic acid,gallic acid and protocatechuic acid in blueberry wine for the first time.In order to get the optimum conditions of separation,the effects of working electrode potential,pH value and concentration of running buffer,separation voltage and injection time on CE-AD were investigated.Under the optimum conditions, the analytes could be separated in Na₂B₄O₇-KH₂PO₄ buffer at pH 7.8 within 18 min.A 300μm diameter carbon disk electrode had good current responses at +0.95 V（vs.SCE） for all analytes.The responses were linear with concentrations over three orders of magnitude with detection limits（S/N = 3） at 10^-8 g/mL magnitude for the analytes and the recoveries were in the range of 95.8- 106.7%.The method could be successfully applied to the analysis of real sample with satisfactory results and therefore recommended for use by the quality control departments of fruit wine producers.     

Determination of strychnine and brucine in traditional Chinese medicine preparations by capillary zone electrophoresis with micelle to solvent stacking

A novel micelle to solvent stacking on-line sample preconcentration technique in capillary zone electrophoresis（MSS-CZE） has been developed to determine the strychnine and brucine in traditional Chinese medicine preparations.The optimal running buffer was 30 mmol/L H₃PO₄ containing 20%acetonitrile at pH 4.0.The sample matrix was 8 mmol/L H₃PO₄ containing 5 mmol/L sodium dodecyl sulfate（SDS） at pH 3.0.The established MSS-CZE method afforded more than 50-fold improvements in concentration sensitivity compared with typical CZE-UV analysis.The calibration curve was linear in the range from 0.2 to 15.0μg/ mL for both strychnine and brucine,with correlation coefficients of 0.9984 and 0.9976,respectively.The limits of detection（5/ N = 3:1） for strychnine and brucine were 0.02 and 0.05μg/mL,respectively.The MSS-CZE method has been successfully applied to the analysis of strychnine and brucine in Chinese medicinal preparations.     

TRANSPORTATION THEORY OF MULTIPLE SCATTERING AND ITS APPLICATION TO SEISMIC CODA WAVES OF IMPULSE SOURCE

The energy distribution of elastic waves in an infinite elastic medium with uniformly and randomly distributed scatterers has been researched. The scattering process is assumed to be isotropic and without conversions between wave types. We get the equation on the distribution of energe density in time and space covering single as well as multiple scattering. Taking physical symmetry of the field into account, it can be simplified. In the case of small earthquakes, the energy source of elastic waves can be assumed as a short pulse emitted isotropically at t=0. The first-order approximate solution in the 3-dimensional space can be obtained, and it is equivalent to Sato's solution for single scattering. In the 2-dimensional space the complete analytical solution has been derived by the mathematical inductance which leads to a conclusion that the codas of surface waves can give the Q-factor related to intrinsic absorption. The equation obtained in this paper is more general.     

Separation of aminophenol isomers in polyelectrolyte multilayers modified PDMS microchip

The separation of three kinds of aminophenol isomers were achieved within 1 min in polyelectrolytes multilayers modified PDMS microchips by layer-by-layer assembly with electrochemical detection (EC). Two polyelectrolytes, poly(dially dimethyl ammonium chloride) (PDDA) and poly(sodium-4-styrene-sulfonate) (PSS) were used to form polyelectrolyte multilayers (PEMs). The surface characteristic of the modified microchip was studied by XPS. The electroosmotic flow (EOF) on PEMs modified PDMS microchips was more stable than that of the native PDMS microchips and the adsorption of samples was greatly reduced on PEMs modified PDMS microchips during the electrophoretic process. The column efficiencies on PEMs modified microchip were increased by 100 times and the signals enhanced by 2 times compared with those of native microchips. The separation conditions such as running buffer pH, running buffer concentration and separation voltage were also optimized.     

Determination of chloride, chlorate and perchlorate by PDMS microchip electrophoresis with indirect amperometric detection

In this work, chloride, chlorate and perchlorate are fast separated on PDMS microchip and detected via in-channel indirect amperometric detection mode. With PDMS/PDMS microchip treated by oxygen plasma, anions chloride (Cl-), chlorate (ClO3-), and perchlorate (ClO4-) are separated within 35s. Some parameters including buffer salt concentration, buffer pH, separation voltage and detection potential are investigated in detail. The separation conditions using 15 mM (pH 6.12) of 2-(N-morpholino)ethanesulfonic acid (MES)+L-histidine (L-His) as running buffer, -2000 V as separation voltage and 0.7 V as detection potential are optimized. Under this condition, the detection limits of Cl-, ClO3-, and ClO4- are 1.9, 3.6, and 2.8 microM, respectively.     

Electroosmotic flow-switchable poly(dimethylsiloxane) microfluidic channel modified with cysteine based on gold nanoparticles

An electroosmotic flow (EOF)-switchable poly(dimethylsiloxane) (PDMS) microfluidic channel modified with cysteine has been developed. The native PDMS channel was coated with poly(diallyldimethylammonium chloride) (PDDA), and then gold nanoparticles by layer-by-layer technique was assembled on PDDA to immobilize cysteine. The assembly was followed by infrared spectroscopy/attenuated total reflection method, contact angle, EOF measurements and electrophoretic separation methods. EOF of this channel can be reversibly switched by varying the pH of running buffer. At low pH, the surface of channels is positively charged, EOF is from cathode to anode. At high pH, the surface is negatively charged, EOF is from anode to cathode. At pH 5.0, near the isoelectric point of the chemisorbed cysteine, the surfaces of channels show neutral. When pH is above 6.0 or below 4.0, the magnitude of EOF varies in a narrow range. And the modified channel surface displayed high reproducibility and good stability, a good reversibility of cathodic-anodic EOF transition under the different pH conditions was observed. Separation of dopamine and epinephrine as well as arginine and histidine were performed on the modified chip.     

Microchip with an open tubular immobilized ph gradient for UV whole column imaging detection

This study reports a new method for establishing an open tubular IPG in a microchip coupled with a whole column image detection (WCID) system for protein separation applications. This method allows a wider range of immobilized pH (2.6–9.5) to be established in a PDMS/quartz channel by controlling the diffusion of acidic and basic polymer solutions into the channel through well‐designed channel dimensions. The developed pH gradient was experimentally validated by performing the separation of a mixture of standard pI markers. It was further validated by the separation of the hemoglobin control AFSC sample. This method is advantageous over existing IPG methods because it has a wider range of pH and maintains the open tubular feature that matches the UV WCID to improve the sensitivity.     

Surface modification of poly(dimethylsiloxane) microchips using a double-chained cationic surfactant for efficiently resolving fluorescent dye adsorption

This paper described a double-chained cationic surfactant, didodecyldimethylammonium bromide (DDAB), for dynamic surface modification of poly(dimethylsiloxane) (PDMS) microchips to reduce the fluorescent dyes adsorption onto the microchannel. When DDAB with a high concentration was present as the dynamic modification reagent in the running and sample buffer, it not only reversed the direction of electroosmotic flow, but also efficiently suppressed fluorescent dyes pyronine Y (PY) or rhodamine B (RB) adsorption onto the chip surface. In addition, vesicles formed by DDAB in the buffer with higher surface charge density and electrophoretic mobility could provide wider migration window and potential for the separation of compounds with similar hydrophobicity. Factors affecting modification, such as pH and concentrations of the buffer, DDAB concentration in the buffer were investigated. Compared with commonly used single-chained cetyltrimethylammonium bromide, DDAB provided a better modification performance. Furthermore, PY and RB were separated successfully on a PDMS microchip at the appropriate conditions with DDAB.     

Application of ionic liquid as additive in determination of three β‐agonists by capillary electrophoresis with amperometric detection

CE coupled with amperometric detection method was developed using ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMImBF₄) as additive for the simultaneous detection of clenbuterol (CLB), terbutaline (TER), and ractopamine (RAC) in feed. The effects of detection potential, concentration of EMImBF₄, pH, and concentration of the running buffer, separation voltage as well as injection time on the separation and detection of these three β‐agonists were investigated in detail. Under the optimum conditions: the detection potential at 1.05 V, 50 mmol/L Tris‐HAc at pH 8.0 with 0.6% (v/v) EMImBF₄, electrokinetic injection 6 s at 16 kV and separation voltage at 16 kV, a baseline separation for these three analytes could be achieved within 11 min. Introduction of EMImBF₄ into the running buffer resulted in significant improvement in separation selectivity and enhancement in peak currents for those β‐agonists, especially for TER and RAC, which could not be separated in the running buffer without additive. The method exhibited wide linear range with LOD (S/N = 3) of 2, 1, and 2 nmol/L for CLB, TER, and RAC, respectively. The precision was determined in both intraday (n = 5) and interday (n = 3) assays, and the RSDs for both migration time and peak current were less than 6%. The proposed method was also applied to analyze β‐agonists in feed sample.     

Simultaneous determination of deoxycytidine diphosphate and deoxycytidine triphosphate by capillary electrophoresis with transient isotachophoretic stacking: a sensitive monitoring method for ribonucleotide reductase activity

A simple and rapid capillary electrophoretic method was developed for simultaneous determination of sub‐micromolar 2′‐deoxycytidine 5′‐diphosphate (dCDP) and 2′‐deoxycytidine 5′‐triphosphate (dCTP) levels in enzyme assays without using radioactively labeled substrates. The separation was performed at 25°C using MES in the BGE as the terminating ion, the chloride ions in the sample buffer as the leading ion, and PEG 4000 in the BGE as the EOF suppressor for sample stacking by transient isotachophoresis (tITP). Several parameters affecting the separation were investigated, including the pH of the BGE, the concentration of sodium chloride in the sample buffer, and the concentrations of MES and PEG 4000 in the running buffer. Good separation with high separation efficiency was achieved within 6 min under optimal conditions. In comparison with the simple CZE method, the present tITP‐CZE method enabled a 150‐fold increase in the injection time without any decrease in resolution and the sensitivity was enhanced up to two orders of magnitude with the new method. The linear range of the method was 0.1–10 μM for dCDP and dCTP. The limits of detection of dCDP and dCTP were 85 and 73 nM, respectively. The proposed method was successfully applied for the activity assay of ribonucleotide reductase from Hep G2 and Sf9 cells.     

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.     

Fast and simple sample introduction for capillary electrophoresis microsystems

A newly designed capillary electrophoresis (CE) microchip with a simple and efficient sample introduction interface is described. The sample introduction is carried out directly on the separation channel through a sharp inlet tip placed in the sample vial, without an injection cross, complex microchannel layouts or hardware modification. Alternate placement of the inlet tip in vials containing the sample and buffer solutions permits a volume defined electrokinetic sample introduction. Such fast and simple sample introduction leads to highly reproducible signals with no observable carry over between different analyte concentrations. The performance of the system was demonstrated in flow-injection and CE measurements of nitroaromatic explosives and for on-chip enzymatic assays of glucose in the presence of ascorbic acid. Employing an 8 cm long separation channel and a separation voltage of 4000 V it offers high-throughput flow-injection assays of 100 samples h(-1) with a relative standard deviation of 3.7% for TNT (n= 100). Factors influencing the analytical performance of the new microchip have been characterized and optimized. Such ability to continuously introduce discrete samples into micrometer channels indicates great promise for high-speed microchip analysis.