Design and fabrication of poly(dimethylsiloxane) electrophoresis microchip with integrated electrodes

A novel poly(dimethylsiloxane) (PDMS) microchip integrated with platinum electrodes has been designed and fabricated using the Micro-electro-mechanical-systems (MEMS) technology. Since high voltage electrodes are integrated on the glass wafer using lift-off process, the microchip is a friendly-to-use system that does not need any extra mechanical apparatus for electrode insertion. To improve the sealing of microchip and ensure the uniformity of microchannel material, one PDMS membrane is formed on glass wafer with electrodes by pressing method. In this study, integrated microchip has been demonstrated as a capillary electrophoresis device for amino acids and satisfactory separation was achieved under separation electrical field strengths of 200 V/cm. The overall performance suggests that this novel microchip is advantageous and practical for the fabrication of lab-on-a-chip.     

Zone electrophoresis of proteins in poly(dimethylsiloxane) (PDMS) microchip coated with physically adsorbed amphiphilic phospholipid polymer

The zone electrophoresis of protein in poly(dimethylsiloxane) (PDMS) microchip coated with the physically adsorbed amphiphilic phospholipid polymer (PMMSi) was investigated. PMMSi was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 3-(methacryloyloxy) propyltris (trimethylsiloxy) silane (MPTSSi) units in a random fashion. The membrane of PMMSi can be formed on the PDMS surface by a simple and quick dip-coating method. The membrane showed high hydrophilicity and good stability in water, as determined by contact angle measurement, fourier-transformed infrared absorption by attenuated total reflection (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. High suppression of protein adsorption to the PDMS surface and reduction in electroosmotic flow (EOF) were achieved by PMMSi coating due to an increase of hydrophilicity, and a decrease of the ζ-potential on the surface of PDMS. For zone electrophoresis, the PMMSi30 containing 30 % hydrophilic MPC was the most suitable molecular design in terms of the stability of the coated membrane on PDMS surface. The average value of EOF mobility of PDMS microchip coated with PMMSi30 was 1.4 × 10^?4 cm² V^?1 s^?1, and the RSD was 4.1 %. Zone electrophoresis of uranine was further demonstrated with high repeatability and reproducibility. Separation of two FITC-labeled proteins (BSA and insulin) was performed with high efficiency and resolution compared with non-treated PDMS microchip.     

去甲肾上腺素在聚色氨酸修饰电极上的电化学行为

制备了聚色氨酸修饰电极,研究了去甲肾上腺素在聚合物薄膜上的电化学行为,实验结果表明:在pH6.0的0.10mol/L磷酸盐缓冲溶液中,聚色氨酸薄膜对去甲肾上腺素的电化学氧化具有明显的催化作用,并可排除抗坏血酸的干扰。去甲肾上腺素检测的线性范围是4.5×10-7～3.0×10-5mol/L;检出限为6.5×10-8mol/L。该修饰电极具有良好的灵敏度、选择性和稳定性,已用于针剂样品分析。     

A bead-based single nucleotide polymorphism (SNP) detection using melting temperature on a microchip

Single nucleotide polymorphism (SNP) is not only one of the most common genetic variances in a human genome, but it also serves a crucial biomarker greatly affecting the phenotypes of individuals. Moreover, SNP had shown its importance by making contributions in many aspects, including species classification for pests, pesticide resistance detection, and disease diagnostic for human beings. Most of today’s SNP detection techniques utilize enzymes or modification of DNA, leading to the requirement of high reagent cost or complex procedures. Therefore, a new SNP genotyping scheme has been developed to address these issues by conducting melting curve analysis on the DNA target sequences, which are conjugated onto polystyrene microbeads in a microfluidic device. The microbeads function as a solid vehicle for capturing the DNA duplexes, providing a larger surface-to-volume ratio for reaction and allowing it to be hydrodynamically confined for melting curve analysis. A prototype device serving as a basis for this proposed scheme was successfully tested, detecting the SNP of ataxia–telangiectasia-mutated gene from both synthetic DNA and genomic DNA of Landrace sows. This bead-based SNP detection only required a minimal reagent amount and simplified the sample preparation procedures, thereby preserving it as a flexible and accurate detection scheme. All these characteristics show great promise in this bead-based SNP detection.     

铜掺杂聚L-天冬氨酸修饰电极同时测定多巴胺和尿酸

用循环伏安法制备了铜掺杂聚L-天冬氨酸修饰玻碳电极,研究了多巴胺（DA）和尿酸（UA）在该修饰电极上的电化学行为,建立了同时测定DA和UA的新方法。在pH3．5的磷酸盐缓冲溶液中,扫描速率为120mV]s时,DA和UA在该电极上产生氧化还原峰,峰电位分别为Eps=0．429V、Epc=0．336V（DA）和Eps=0．617V（UA）,DA和UA的氧化峰分开达0．188V。采用循环伏安法（CV法）和示差脉冲伏安法（DPVs法）同时测定DA和UA的线性范围分别为：DA：3．00×10^-6-4．00×100mol／L、4．00×10^-5～1．00×10^-4mlo/L（CV）、3．00×10^-7～3．00×10^-6mol／L、3．00×10^-6—1．00×10^-5mol／L（DPVs）,UA：8．00×10^-6～5．00×10^-5mol／L、5．00×10^-5-2．00×10^-4mol／L（CV）、3．00×10^-7～5．00×10^-5mol／L、5．00×10^-5．2．00×10^-4mol／L（DPVs）;检出限分另U为8．0×10^-7mol／L、1．0×10^-6mol／L（CV）和3．0×10^-7mol/L、3．0×10^-7mol／L（DPVs）。用于人体尿液中DA和UA的同时测定,结果满意。     

Inner surface modification of poly(dimethylsiloxane) microchannel with chitin for electrophoretic analysis of proteins

Microchip electrophoresis in a poly(dimethylsiloxane) microfluidic device is one of the versatile separation techniques in a micro total analysis system, while an unstable electroosmotic flow depending on an inner surface of a microchannel and a nonspecific adsorption of biogenic compounds onto the inner surface are often problematic in microchip electrophoresis. To overcome these drawbacks, a chitin-coated poly(dimethylsiloxane) microchannel was newly developed by a relatively simple experimental procedure based on vacuum drying. The obtained chitin-coating showed high durability during 10-times experiments with a stable electroosmotic flow. It was also confirmed that the chitin-coated poly(dimethylsiloxane) microchannel provided the pH-dependent electroosmotic flow related to the dissociations of amino and silanol groups of chitin and poly(dimethylsiloxane), respectively. The nonspecific adsorption of fluorescently labeled proteins onto the inner surface of the channel was well suppressed by the coating, resulting in the sharp and symmetric peak without tailing in the microchip electrophoretic analysis of proteins. The separation of the proteins was also demonstrated in the chitin-coated microchannel, so that the resolution and reproducibility of the migration time were improved as compared to those in the untreated microchannel.     

聚（3-甲基噻吩）修饰电极的制备及其用于多巴胺的电化学行为及测定研究

通过实验研究了恒电流法制备聚(3-甲基噻吩)(P3MT)修饰玻碳电极的最佳聚合条件,并用扫描电子显微镜(SEM)对制备的修饰电极进行了表征.利用最佳条件下制备的聚(3-甲基噻吩)修饰电极,研究了多巴胺(DA)在该修饰电极上的电化学行为,并建立了多巴胺的电化学测定方法.实验结果表明,用该方法制备的修饰电极比用循环伏安法(CV)和恒电位氧化相结合制备的电极性能更好.     

用聚合亚甲蓝修饰的酶电极进行青霉素残留的测定研究

将青霉素酶与亚甲蓝用循环伏安法共聚合到玻碳电极上,制成青霉素酶电极,通过交流阻抗谱对酶电极表征.研究了聚合亚甲蓝在不同pH值下,酸催化还原反应的活化能随pH值的变化.在一定电位范围内,青霉素微小浓度变化与亚甲蓝循环伏安还原峰电流成正比,据此可间接测定牛奶中残留青霉素含量,分别利用计时电流法和循环伏安法在磷酸缓冲溶液和牛奶中测量,计时电流法的线性范围分别为1.40×10-4～2.81×10-3mmol/L和5.61×10-4～2.81×10-3mmol/L,循环伏安法的线性范围分别为2.81×10-4～2.81×10-3mmol/L和1.12×10-3～2.81×10-3mmol/L.     

Evaluation of passive mixing behaviors in a pillar obstruction poly(dimethylsiloxane) microfluidic mixer using fluorescence microscopy

The rapid mixing of fluids passing through a microfluidic channel is very important for various applications of microfluidic systems. It has been a great challenge to achieve highly efficient mixing in a microfluidic system because it is very difficult to generate turbulence in a submillimeter-size channel at low Reynolds numbers (Re). In this paper, we fabricated a pillar obstruction microfluidic mixer and evaluated its mixing efficiency at various flow rates. The mixing behavior of confluent streams was estimated using a fluorescence microscope. Three different sets of miscible solutions (phosphate-buffered solution, gold nanocolloids and 20% glycerol), with Rhodamine 6G aqueous solution, were used as sample laminar flows. According to our experimental results, the pillar obstruction microfluidic mixer shows an excellent mixing performance in the low Re range. Here, the mixing performance was strongly dependent on the characteristic viscosity changes of different sets of miscible solutions. The pillar obstruction microfluidic mixer designed here is expected to benefit a wide range of lab-on-a-chip applications because fabrication is very simple and the mixing efficiency is excellent at low Re.     

Development of an ultrafast quantitative heterogeneous immunoassay on pre-functionalized poly(dimethylsiloxane) microfluidic chips for the next-generation immunosensors

Although the reaction time for antigen-antibody binding has been greatly reduced in microchannels, other processes in heterogeneous immunoassays (HEIs), such as blocking and antigen adsorption have not benefited from miniaturization as a reduction in size to micro dimensions does not increase the speed of these processes significantly. The overall assay time of reported microfluidic HEIs has continued to be limited by these processes. In this study, we successfully develop an ultrafast quantitative HEI with pre-functionalized microfluidic poly(dimethylsiloxane) (PDMS) chips. The protein A functionalized PDMS surface is found to be highly effective in reducing the antigen adsorption time in microchannels. The functionalized surfaces can be stable at least for 2.5 months when stored at 4°C in a buffer solution consisting of 10 mM Tris, 0.05% bovine serum albumin, 0.05% Proclin 300, and 5% glycerol. In addition, the immunosorption process, which is substantially accelerated in micro scale, results in a significant reduction in nonspecific binding. The time of blocking step can therefore be reduced to a minimum or can be eliminated. The overall assay for detecting bovine immunoglobulin G is completed in 19 min with a limit of detection of 3.8 nM. The ultrafast analysis time and superior sensitivity demonstrated by this microfluidic HEI is promising for being used to develop the next-generation immunosensors.     

三聚氰胺修饰电极同位镀铋膜测定镉离子

采用电聚合方法制备三聚氰胺修饰玻碳电极(PM/GC),然后在其表面同位镀铋膜,研究Cd2+在该电极上的溶出伏安行为,并与裸玻碳电极(GC)同位镀铋膜电极上Cd2+的溶出伏安行为进行比较.研究表明,镉在同位镀铋膜的PM/GC电极上可得到灵敏的溶出峰.在优化的实验条件下,镉的氧化峰电流与其在1.0×10～1.O×10-6mol/L浓度范围内呈良好的线性关系,检测下限为5.0×10-8mol/L.由于每次溶出后可方便地将铋膜溶解更新,该方法重现性好.使用铋膜电极替代汞膜电极还有利于保护环境.     

Anodic stripping voltammetric determination of copper(II) using a functionalized carbon nanotubes paste electrode modified with crosslinked chitosan

The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichlorohydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L⁻¹ KNO₃ with pH adjusted to 2.25 with HNO₃, an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L⁻¹ KCl) for 300 s and a scan rate of 100 mV s⁻¹. Under these optimal experimental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10⁻⁸ to 1.60 × 10⁻⁵ mol L⁻¹ with a detection limit of 1.00 × 10⁻⁸ mol L⁻¹. The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.     

Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the composition of the oxidizing plasma

Controlled surface oxidation of polydimethylsiloxane (PDMS) is essential for permanent adhesion between device components composed of this elastomer. The permanent adhesion between such microdevice components results from covalent crosslinking across the interfaces between PDMS and other silica-based materials, such as glass, quartz, and PDMS. Optimal duration and conditions of oxidation, attained via treatments with oxygen-containing plasma, are crucial for microfabrication procedures with quantitative yields. While insufficient PDMS oxidation does not provide high enough surface density of siloxyl groups for cross-interface linking, overoxidation of PDMS yields rough silica surface layers that prevent the adhesion between flat substrates. Ideally, for a set of plasma conditions, the range of treatment durations producing permanent adhesion should be as broad as possible: i.e., the surface oxidation of PDMS sufficient for irreversible binding has to complete significantly before the effects of overoxidation become apparent. Such a requirement assures that relatively small fluctuations in the treatment conditions will not result in over- or under-oxidation and, hence, will not compromise the yields of the fabrication procedures. We examined the dependence of the quality of adhesion (QA) between plasma-treated PDMS and glass substrates on the composition of the oxygen-containing plasma and on the radio frequency (RF) of the plasma generator. We observed that plasma generated at megahertz RF provided superior conditions than kilohertz RF. Concurrently, an increase in the oxygen content of binary gas mixtures, used for the plasma, broadened the treatment durations that afford superior QA.     

Using of hydrogen ion-selective poly(vinyl chloride) membrane electrode based on calix[4]arene as thiocyanate ion-selective electrode

A hydrogen ion-selective electrode (ISE) is prepared by using 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetracyanometoxy-calix[4]arene and an investigation about whether it could be used as a thiocyanate ion-selective electrode is made by using its characteristic of becoming thiocyanate sensitive in acidic regions. The electrode of the optimum characteristic has a composition of 1% ionophore, 66% 2-NPOE and 33% poly(vinyl chloride) (PVC). This electrode exhibits a linear response over the range 1.0 × 10⁻¹ to 3.0 × 10⁻⁵ M of thiocyanate with a slope of 52.0 ± 0.2 mV/pSCN. The effects of the pH and the membrane composition are also investigated. The lifetime of the electrode is at least 4 months and its response time is found to be 10–15 s. The selectivity coefficients of some anions are calculated by using mixed solution interference method. Application of the electrode to the potentiometric titration of thiocyanate ion with silver nitrate is reported. There is a good agreement between the results obtained by the proposed electrode and the Mohr method at 95% confidence level.     

N，N-双（2-氨基苯基）草酸二酰胺合铜（Ⅱ）配合物为中性载体的高选择性硫氰酸根电极的研究

该文以N,N-双(2-氨基苯基)草酸二酰胺合铜(Ⅱ)[Cu(Ⅱ)-BAPO]为中性载体,制备了一种对硫氰酸根(SCN-)具有优良的电位响应特性并呈现出反Hofmeister选择性行为的离子电极,其选择性次序为:SCN-＞ClO4-＞I-＞Sal-＞NO3-＞Cl-＞NO2-＞CH3COO-＞SO42-＞F-＞PO43-.该电极在pH=5.0的磷酸盐缓冲体系中具有最佳的电位响应,在1.0×10-5～1.0×10-1mol/L SCN-浓度范围呈近能斯特响应,斜率为-67.5 mV/pSCN-(25℃),检测下限为4.0×10-6mol/L.采用紫外光谱分析技术研究了配合物中心金属原子以及配合物本身的结构对电极电位响应行为的作用机理.将该电极用于废水分析,结果令人满意.     

Locked nucleic acids biosensor for detection of BCR/ABL fusion gene using benzoate binuclear copper (II) complex as hybridization indicator

Benzoate binuclear copper (II) complex, [Cu₂(C₇H₅O₂)₄(C₂H₆O)₂] (abbreviated as CuR₂) was prepared and its interaction with double-stranded salmon sperm DNA (dsDNA) in pH 7.4 phosphate buffer solution was studied by electrochemical experiments at the Au electrode (AuE). It was revealed that CuR₂ presented an excellent electrochemical activity on AuE and could bind with dsDNA by intercalation mode. The CuR₂ was further utilized as a new indicator in the fabrication of an electrochemical DNA biosensor for detection of BCR/ABL fusion gene. The biosensor based on nanogold (NG) modified AuE was developed by using thiolated-hairpin locked nucleic acids (LNA) as the capture probe for hybridization with BCR/ABL fusion gene. The results indicated this new method has excellent specificity for single-base mismatch and complementary after hybridization. The constructed electrochemical DNA biosensor achieved a detection limit of 1.0 × 10⁻¹⁰ M for complementary target DNA with a good stability.     

戊二醛双缩肼基二硫代甲酸苄酯为中性载体的新型镍离子选择电极的研究

研究了以戊二醛双缩肼基二硫代甲酸苄酯(GABSB)为中性载体的阳离子选择电极,结果表明:该电极对Ni2+有优良的电位响应性能和选择性,在pH=3.0的硝酸盐缓冲条件下对Ni2+的线性响应范围为7.6×10-6～1.0×10-1 mol/L,斜率为31.0 mV/dec(25℃),检测下限为4.2×10-6 mol/L.采用紫外-可见光谱和交流阻抗分析技术研究了电极的响应机理.该电极具有响应快、检出限低、制备简单等优点,将该电极应用于电位滴定,结果令人满意.     

Efficiency enhancement in blue organic light emitting diodes with a composite hole transport layer based on poly(ethylenedioxythiophene):poly(styrenesulfonate) doped with TiO2 nanoparticles

Blue color organic/polymeric light emitting diodes are very important because they can be used for tri-color display applications, fluorescence imaging, and exciting yellow phosphor for generating white light for general illumination. But the efficiency of blue organic/polymeric light emitting diodes is considerably low due to their large band gap that requires higher energy for effective emission. In this paper we report the enhancement in polyfluorene blue organic light emitting diodes with a polymer nano-composite hole transport layer. Blue light emitting diode based on polyfluorene as an emissive layer and poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate)–titanium dioxide nanocomposite as the hole transport layer were fabricated and studied. Different concentrations of titanium dioxide nanoparticles were doped in poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) in the hole transport layer and the performance of the devices were studied. Significant enhancement in the blue peak at 430 nm of polyfluorene has been observed with increase in concentration of TiO₂ nanoparticles in the hole transport layer. The turn on voltage of the device has also been found to improve significantly with the incorporation of titanium dioxide nanoparticles in the hole transport layer. The optimized concentration of titanium dioxide in the hole transport layer for most efficient device has been found to 15 wt.%.     

Development of an optical fibre reflectance sensor for copper (II) detection based on immobilised salicylic acid

Immobilized salicylic acid onto XAD-2 (styrene–divinylbenzene cross-linked copolymer) has been attempted in this study as a reagent phase for the development of an optical fibre copper (II) sensor. The measurements were carried out at a given wavelength of 690.27 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the analyte element. The optimum response was obtained at pH 5.0. The linear dynamic range of Cu(II) was found within the concentration range of 1.0–2.0 mmol L⁻¹ with its LOD of 0.5 mmol L⁻¹. The sensor response from different probes (n = 9) gave an R.S.D. of 8.4% at 0.55 mmol L⁻¹ Cu(II). The effect of interfered ions at 1:1 molar ratio of Cu(II):foreign ion was also studied in this work.     

聚L-苯丙氨酸/石墨烯修饰电极测定左旋多巴

将玻碳电极(GCE)放入L-苯丙氨酸(LP)和氧化石墨烯(GO)的混合液中进行循环伏安扫描聚合,该过程中GO通过电化学还原成石墨烯(ERGO),因而得到聚L-苯丙氨酸/石墨烯修饰电极(PLP-ERGO/GCE),该电极对左旋多巴(LDA)具有较好的催化能力和较快的电子传递速率。利用循环伏安法(CV)和差分脉冲伏安法(DPV)探究了LDA在该电极上的电化学行为,LDA在电极表面的氧化还原过程受扩散控制。在最佳实验条件下,LDA在0.478 V处产生一个氧化峰。采用DPV法测定LDA的线性范围为7.50×10-6~2.50×10-4 mol/L,检出限为7.5×10-7 mol/L。用于样品中左旋多巴的测定,结果满意。