Characterization of electrophoretic behavior of sugar isomers by microchip electrophoresis coupled with videomicroscopy

Electric Field-Driven On-Request Instant in Situ Formation/Removal of Solid Hydrogel within Microchannels for Efficient Electrophoretic Separation

Electrophoretic separation in short microchannels is a promising way for rapid analysis of biomolecules, but the pressurized laminar flow may compromise the separation efficiency. In this work, through an electric field, instant formation and removal of a solid chitosan/β-glycerol phosphate (CS/β-GP) hydrogel within microchannels of microchips were realized. In a typical cross-type microchip, the CS/β-GP hydrogel was precisely formed in the separation microchannel within 15 s of the application of a voltage of 2000 V. Highly efficient separation of peptides and proteins was achieved, and theoretical plate numbers of 0.6 to 1.5 × 10⁶/m were attained for proteins in 120 s. The used hydrogel could be swiftly removed also with an electric field, and the whole procedure was achieved on a standard microchip electrophoresis device with no extra accessory or special operation required.

Capillary electrophoresis-mass spectrometry for direct structural identification of serum N-glycans

Through direct coupling of capillary electrophoresis (CE) to mass spectrometry (MS) with a sheathless interface, we have identified 77 potential N-glycan structures derived from human serum. We confirmed the presence of N-glycans previously identified by indirect methods, e.g., electrophoretic mobility standards, obtained 31 new N-glycan structures not identified in our prior work, differentiated co-migrating structures, and determined specific linkages on isomers featuring sialic acids. Serum N-glycans were cleaved from proteins, neutralized via methylamidation, and labeled with the fluorescent tag 8-aminopyrene-1,3,6-trisulfonic acid, which renders the glycan fluorescent and provides a -3 charge for electrophoresis and negative-mode MS detection. The neutralization reaction also stabilizes the labile sialic acids. In addition to methylamidation, native charges from sialic acids were neutralized through reaction with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium to amidate α2,6-linked sialic acids in the presence of ammonium chloride and form lactones with α2,3-linked sialic acids. This neutralization effectively labels each type of sialic acid with a unique mass to determine specific linkages on sialylated N-glycans. For both neutralization schemes, we compared the results from microchip electrophoresis and CE.

Structural Characterization of Serum N-Glycans by Methylamidation, Fluorescent Labeling, and Analysis by Microchip Electrophoresis

To characterize the structures of N-glycans derived from human serum, we report a strategy that combines microchip electrophoresis, standard addition, enzymatic digestion, and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). We compared (i) electrophoretic mobilities of known N-glycans from well-characterized (standard) glycoproteins through standard addition, (ii) the electrophoretic mobilities of N-glycans with their molecular weights determined by MALDI-MS, and (iii) electrophoretic profiles of N-glycans enzymatically treated with fucosidase. The key step to identify the sialylated N-glycans was to quantitatively neutralize the negative charge on both α2,3- and α2,6-linked sialic acids by covalent derivatization with methylamine. Both neutralized and nonsialylated N-glycans from these samples were then reacted with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) to provide a fluorescent label and a triple-negative charge, separated by microchip electrophoresis, and detected by laser-induced fluorescence. The methylamidation step leads to a 24% increase in the peak capacity of the separation and direct correlation of electrophoretic and MALDI-MS results. In total, 37 unique N-glycan structures were assigned to 52 different peaks recorded in the electropherograms of the serum samples. This strategy ensures the needed separation efficiency and detectability, easily resolves linkage and positional glycan isomers, and is highly reproducible.

Light-emitting diodes for analytical chemistry

Light-emitting diodes (LEDs) are playing increasingly important roles in analytical chemistry, from the final analysis stage to photoreactors for analyte conversion to actual fabrication of and incorporation in microdevices for analytical use. The extremely fast turn-on/off rates of LEDs have made possible simple approaches to fluorescence lifetime measurement. Although they are increasingly being used as detectors, their wavelength selectivity as detectors has rarely been exploited. From their first proposed use for absorbance measurement in 1970, LEDs have been used in analytical chemistry in too many ways to make a comprehensive review possible. Hence, we critically review here the more recent literature on their use in optical detection and measurement systems. Cloudy as our crystal ball may be, we express our views on the future applications of LEDs in analytical chemistry: The horizon will certainly become wider as LEDs in the deep UV with sufficient intensity become available.

Microwave-assisted derivatization for fast and efficient analysis of saccharides on disposable microchips

A domestic microwave oven was used to achieve rapid derivatization of saccharides for their microchip electrophoresis analysis.

Microchip electrophoresis at elevated temperatures and high separation field strengths

We report free-solution microchip electrophoresis performed at elevated temperatures and high separation field strengths. We used microfluidic devices with 11 cm long separation channels to conduct separations at temperatures between 22 (ambient) and 45°C and field strengths from 100 to 1000 V/cm. To evaluate separation performance, N-glycans were used as a model system and labeled with 8-aminopyrene-1,3,6-trisulfonic acid to impart charge for electrophoresis and render them fluorescent. Typically, increased diffusivity at higher temperatures leads to increased axial dispersion and poor separation performance; however, we demonstrate that sufficiently high separation field strengths offset the impact of increased diffusivity in order to maintain separation efficiency. Efficiencies for these free-solution separations are the same at temperatures of 25, 35, and 45°C with separation field strengths ≥ 500 V/cm.

Comparative profiling of N-glycans isolated from serum samples of ovarian cancer patients and analyzed by microchip electrophoresis

Ovarian cancer is the fifth leading cause of cancer-related mortalities for women in the United States and the most lethal gynecological cancer. Aberrant glycosylation has been linked to several human diseases, including ovarian cancer, and accurate measurement of changes in glycosylation may provide relevant diagnostic and prognostic information. In this work, we used microchip electrophoresis coupled with laser-induced fluorescence detection to determine quantitative differences among the N-glycan profiles of control individuals and late-stage recurrent ovarian cancer patients prior to and after an experimental drug treatment that combined docetaxel and imatinib mesylate. N-Glycans were enzymatically released from 5-μL aliquots of serum samples, labeled with the anionic fluorescent tag, 8-aminopyrene-1,3,6-trisulfonic acid, and analyzed on microfluidic devices. A 22-cm long separation channel, operated at 1250 V/cm, generated analysis times less than 100 s, separation efficiencies up to 8 × 10(5) plates (3.6 × 10(6) plates/m), and migration time reproducibilities better than 0.1% relative standard deviation after peak alignment. Principal component analysis (PCA) and analysis of variance (ANOVA) tests showed significant differences between the control and both pre- and post-treatment cancer samples and subtle differences between the pre- and post-treatment cancer samples. Area-under-the-curve (AUC) values from receiver operating characteristics (ROC) tests were used to evaluate the diagnostic merit of N-glycan peaks, and specific N-glycan peaks used in combination provided AUCs > 0.90 (highly accurate test) when the control and pretreatment cancer samples and control and post-treatment samples were compared.

N-glycan profiling by microchip electrophoresis to differentiate disease states related to esophageal adenocarcinoma

We report analysis of N-glycans derived from disease-free individuals and patients with Barrett's esophagus, high-grade dysplasia, and esophageal adenocarcinoma by microchip electrophoresis with laser-induced fluorescence detection. Serum samples in 10 μL aliquots are enzymatically treated to cleave the N-glycans that are subsequently reacted with 8-aminopyrene-1,3,6-trisulfonic acid to add charge and a fluorescent label. Separations at 1250 V/cm and over 22 cm yielded efficiencies up to 700,000 plates for the N-glycans and analysis times under 100 s. Principal component analysis (PCA) and analysis of variance (ANOVA) tests of the peak areas and migration times are used to evaluate N-glycan profiles from native and desialylated samples and determine differences among the four sample groups. With microchip electrophoresis, we are able to distinguish the three patient groups from each other and from disease-free individuals.

Analysis of glycans derived from glycoconjugates by capillary electrophoresis-mass spectrometry

The high structural variation of glycan derived from glycoconjugates, which substantially increases with the molecular size of a protein, contributes to the complexity of glycosylation patterns commonly associated with glycoconjugates. In the case of glycoproteins, such variation originates from the multiple glycosylation sites of proteins and the number of glycan structures associated with each site (microheterogeneity). The ability to comprehensively characterize highly complex mixture of glycans has been analytically stimulating and challenging. Although the most powerful MS and MS/MS techniques are capable of providing a wealth of structural information, they are still not able to readily identify isomeric glycan structures without high-order MS/MS (MS(n) ). The analysis of isomeric glycan structures has been attained using several separation methods, including high-pH anion-exchange chromatography, hydrophilic interaction chromatography and GC. However, CE and microfluidics CE (MCE) offer high separation efficiency and resolutions, allowing the separation of closely related glycan structures. Therefore, interfacing CE and MCE to MS is a powerful analytical approach, allowing potentially comprehensive and sensitive analysis of complex glycan samples. This review describes and discusses the utility of different CE and MCE approaches in the structural characterization of glycoproteins and the feasibility of interfacing these approaches to MS.

Physisorbed surface coatings for poly(dimethylsiloxane) and quartz microfluidic devices

Surface modifications of microfluidic devices are of essential importance for successful bioanalytical applications. Here, we investigate three different coatings for quartz and poly(dimethylsiloxane) (PDMS) surfaces. We employed a triblock copolymer with trade name F(108), poly(L-lysine)-g-poly(ethylene glycol) (PLL-PEG), as well as the hybrid coating n-dodecyl-β-D-maltoside and methyl cellulose (DDM/MC). The impact of these coatings was characterized by measuring the electroosmotic flow (EOF), contact angle, and prevention of protein adsorption. Furthermore, we investigated the influence of static coatings, i.e., the incubation with the coating agent prior to measurements, and dynamic coatings, where the coating agent was present during the measurement. We found that all coatings on PDMS as well as quartz reduced EOF, increased reproducibility of EOF, reduced protein adsorption, and improved the wettability of the surfaces. Among the coating strategies tested, the dynamic coatings with DDM/MC and F(108) demonstrated maximal reduction of EOF and protein adsorption and simultaneously best long-term stability concerning EOF. For PLL-PEG, a reversal in the EOF direction was observed. Interestingly, the static surface coating strategy with F(108) proved to be as effective to prevent protein adsorption as dynamic coating with this block copolymer. These findings will allow optimized parameter choices for coating strategies on PDMS and quartz microfluidic devices in which control of EOF and reduced biofouling are indispensable.

Microchip electrophoresis of N-glycans on serpentine separation channels with asymmetrically tapered turns

We designed and fabricated microfluidic devices with serpentine separation channels and asymmetrically tapered turns, thus allowing high efficiency separations and minimizing band broadening associated with the "racetrack" effect. We evaluated the performance of these devices by measuring the variation in separation efficiency with separation length, electric field strength, taper ratio of the turns, and number of turns. N-Glycans derived from ribonuclease B and labeled with 8-aminopyrene-1,3,6-trisulfonic acid were electrophoretically separated on serpentine channels with separation lengths of 11, 18, 22, and 36 cm at electric field strengths from 750 to 1750 V/cm. Separations on the 36-cm channel produced plate numbers up to 940,000 with an analysis time under 3.1 min, whereas separations on the 22-cm channel had a shorter analysis time (less than 1.25 min), still with respectable efficiencies (up to 600,000 plates). Turn-induced dispersion was minimized with taper ratios 2 and 3, whereas having two or four 180° turns along with the separation length did not impact the overall efficiency. The developed device was used to analyze native and desialylated N-glycans derived from the blood serum of an ovarian cancer patient and a disease-free individual. Separation efficiencies similar to that achieved with the model glycans from ribonuclease B were attained for these biological samples.

DNA separation by cholesterol-bearing pullulan nanogels

We present an application of a novel DNA separation matrix, cholesterol-bearing pullulan (CHP) nanogels, for microchip electrophoresis. The solution of the CHP showed a unique phase transition around 30 mg∕ml and formed gel phase over this critical concentration. This gel phase consists of the weak hydrophobic interactions between the cholesterols could be easily deformed by external forces, and thus, loading process of the CHP nanogels into microchannels became easier. The high concentration of the CHP nanogels provided excellent resolutions especially for small DNA fragments from 100 to 1500 bp. The separation mechanism was discussed based on Ogston and Reptation models which had developed in gels or polymer solutions. The result of a single molecule imaging gave us an insight of the separation mechanism and the nanogel structures as well.

Spontaneous adsorption on a hydrophobic surface governed by hydrogen bonding

Spontaneous adsorption from solution onto solid surface is a common phenomenon in nature, but the force that governs adsorption is still a matter of considerable debate. (1, 2) We found that surfactants and cellulose adsorb from solution onto a poly(methyl methacrylate) (PMMA) surface in an ordered and cooperative way governed by hydrogen bonding. The glucose rings of n-dodecyl-beta-D-maltoside (DDM) and hydroxyethylcellulose (HEC) stand perpendicular to the surface, H-bond to the surface COOMe groups with their C=O and Me-O bonds parallel to the surface, and form a tight monolayer. The non-H-bonded COOMe groups orient their C=O bonds perpendicular to the surface. In contrast, the glucose rings of hydrophobically modified hydroxyethylcellulose (HMHEC) lie flat with the side chains perpendicular to the surface and H-bond to the perpendicular-oriented C=O groups. The non-H-bonded COOMe groups orient their C=O bonds parallel but Me-O bonds near-perpendicular to the surface for stabilizing HMHEC. The current work provides a detailed picture of how surface-active molecules interact with a solid surface and self-assemble into greatly different architectures.

Fully integrated microfluidic separations systems for biochemical analysis

Over the past decade a tremendous amount of research has been performed using microfluidic analytical devices to detect over 200 different chemical species. Most of this work has involved substantial integration of fluid manipulation components such as separation channels, valves, and filters. This level of integration has enabled complex sample processing on miniscule sample volumes. Such devices have also demonstrated high throughput, sensitivity, and separation performance. Although the miniaturization of fluidics has been highly valuable, these devices typically rely on conventional ancillary equipment such as power supplies, detection systems, and pumps for operation. This auxiliary equipment prevents the full realization of a "lab-on-a-chip" device with complete portability, autonomous operation, and low cost. Integration and/or miniaturization of ancillary components would dramatically increase the capability and impact of microfluidic separations systems. This review describes recent efforts to incorporate auxiliary equipment either as miniaturized plug-in modules or directly fabricated into the microfluidic device.

Enhanced electrophoretic resolution of monosulfate glycosaminoglycan disaccharide isomers on poly(methyl methacrylate) chips

To improve the separation of monosulfate glycosaminoglycan disaccharide isomers by microchip electrophoresis, we found that addition of 1,4-dioxane (DO) dramatically improved analyte resolution, probably due to solvation effects. Methylcellulose (MC) was tested for the ability to suppress EOF and analyte adsorption to the chip. To improve analyte resolution, buffer pH, beta-CD, and DO were systematically investigated. Fast separation was achieved by increasing the electric field strength, and field-amplified sample stacking occurred with increasing buffer concentrations. Therefore, based on our findings, we describe an efficient method for the separation of monosulfate and trisulfate unsaturated disaccharides (DeltaDi-UA2S, DeltaDi-4S, DeltaDi-6S, and DeltaDi-triS) derivatized with 2-aminoacridone hydrochloride. A mixture of monosulfate disaccharide isomers (DeltaDi-UA2S, DeltaDi-4S, and DeltaDi-6S) was baseline-separated within 75 s on a poly(methyl methacrylate) chip using a mixed buffer (DO/running buffer 57:43 v:v), 0.5% MC, pH 6.81, with an E(sep) of 558 V/cm. The theoretical plate was in the range of 5 x 10(5) to 1 x 10(6) m-1.

Recent developments in optical detection methods for microchip separations

This paper summarizes the features and performances of optical detection systems currently applied in order to monitor separations on microchip devices. Fluorescence detection, which delivers very high sensitivity and selectivity, is still the most widely applied method of detection. Instruments utilizing laser-induced fluorescence (LIF) and lamp-based fluorescence along with recent applications of light-emitting diodes (LED) as excitation sources are also covered in this paper. Since chemiluminescence detection can be achieved using extremely simple devices which no longer require light sources and optical components for focusing and collimation, interesting approaches based on this technique are presented, too. Although UV/vis absorbance is a detection method that is commonly used in standard desktop electrophoresis and liquid chromatography instruments, it has not yet reached the same level of popularity for microchip applications. Current applications of UV/vis absorbance detection to microchip separations and innovative approaches that increase sensitivity are described. This article, which contains 85 references, focuses on developments and applications published within the last three years, points out exciting new approaches, and provides future perspectives on this field.

Semihydrodynamic Injection for High Salt Stacking and Sweeping on Microchip Electrophoresis and Its Application for the Analysis of Estrogen and Estrogen Binding

In this work, a semihydrodynamic (SHD) injection method was introduced and coupled with high salt stacking and electrokinetic chromatography for the analysis of estrogen and estrogen binding using a simple cross microchannel. The SHD method allows all samples to be hydrodynamically injected and focused into the separation channel at a relatively high flow rate and without splitting and diffusion, leading to reproducible bias-free injections of larger sample volumes (up to 50 nL) within 3 s. Moreover, the injection method is initiated without voltage switching, leading to a reduced mixing effect. Such advantages are well suited for performing stacking and sweeping on a microchip. We investigated the stacking effect under continuous and discontinuous co-ion conditions as well as under sweeping conditions. Micellar sweeping effect alone was relatively weak (7-8 times), partly due to a lower sodium cholate concentration (30 mM) used for the running buffer. By combining the sweeping effect with high salt stacking, however, up to a 200-300-fold enhancement factor could be achieved, and the high-salt and low-surfactant contents for the running buffer were favorable for binding study under nonequilibrium conditions. To the best of our knowledge, this is the first demonstration of the hydrodynamic injection used for high salt sample stacking on a microchip, also for further combining micellar electrochromatography and affinity separation for the analysis of hydrophobic ligand binding using microchip electrophoresis.

Miniaturized separation techniques in glycomic investigations

High-sensitivity glycomic analyses are becoming of a great interest in modern biomedical and clinical research, as well as in the development of recombinant protein products. The evolution of separation techniques for glycomic analysis at high sensitivity is highlighted in this review. These methodologies include capillary liquid chromatography, capillary electrophoresis (CE) and capillary electrochromatography (CEC). The potential of such methodologies in glycomic analysis is demonstrated for model glycoproteins as well as total glycomes derived from biological samples.

Cationic amylopectin derivatives as additives for analysis of proteins in capillary electrophoresis

Positively charged amylopectin, which is a major constituent of cationic starch, was used to modify the inner surface of fused-silica capillaries by addition to the running solution, which was subsequently employed in CE. Capillaries filled with cationic amylopectin derivatives were shown to generate a stable reversed EOF in the investigated range of pH 4-8. Among the additives studied, quaternary ammonium amylopectin derivatives with high amino and low hydroxypropyl groups showed fast electroosmotic mobility and very effectively suppressed the adsorption of proteins. The run-to-run and batch-to-batch repeatability of the procedures were satisfactory with RSDs of 0.5% and 2.4%, respectively. A basic protein, alpha-chymotrypsinogen, migrated within 6 min and the theoretical plate number of it reached 560 000 plates/m.

Rapid analysis of oligosaccharides derived from glycoproteins by microchip electrophoresis

A novel method for fast profiling of complex oligosaccharides released from glycoproteins based on microchip electrophoresis (mu-CE) is presented here. The characterization of separation conditions, i.e., the composition, concentration and pH of running buffer as well as the applied voltage, has been performed using maltose (G2), cellobiose ( G2'), maltriose (G3) and panose (G3') as oligosaccharide isomer models. In mu-CE, much better separation of oligosaccharide isomers and oligosaccharide ladder was obtained in phosphate buffer than in borate buffer over a wide pH range. Under optimal conditions, high-performance separation of the N-linked complex oligosaccharides released from ribonuclease B, fetuin, alpha1-acid glycoprotein (AGP) and IgG was achieved using polymethylmethacrylate (PMMA) microchips with an effective separation channel of 30 mm. These results represent the first reported analysis of the N-linked oligosaccharides derived from glycoproteins by mu-CE, indicating that the present mu-CE-based method is a promising alternative for characterization of the N-linked oligosaccharides in glycoproteins.

Hybrid Dynamic Coating with n-Dodecyl β-d-Maltoside and Methyl Cellulose for High-Performance Carbohydrate Analysis on Poly(methyl methacrylate) Chips

Hybrid dynamic coating using n-dodecyl beta-d-maltoside (DDM) and methyl cellulose (MC) has been developed for suppression of analyte adsorption and electroosmotic flow (EOF) in a poly(methyl methacrylate) (PMMA) channel. The adsorption of APTS-labeled sugars in a PMMA channel was obviously suppressed with DDM dynamic coating; however, EOF was reduced only by a factor of approximately 25%, resulting in irreproducible separations. In contrast, both analyte adsorption and EOF in a PMMA channel were efficiently minimized with MC coating; however, concentrated MC above 0.3% was required to achieve high-performance separations, which greatly increased viscosity of the solution and caused difficulties during buffer loading and rinsing. In addition, n-dodecyltrimethylammonium chloride did not show observable effects on reducing analyte adsorption, although it has the same hydrophobic alkyl chain as DDM. These results strongly indicated that the polysaccharide moiety of surface modifiers has a specific affinity to surface charges and is crucial to achieving efficient and stable dynamic coating on the PMMA surface. Hybrid dynamic coating with 0.25% DDM and 0.03% MC was found to minimize both analyte adsorption and EOF in a PMMA channel to a negligible level, while still keeping a low viscosity of the solution. High-speed and high-throughput profiling of the N-linked glycans derived from alpha1-acid glycoprotein, fetuin, and ribonuclease B was demonstrated in both single-channel and 10-channel PMMA chips using DDM-MC hybrid coating. We propose that DDM-MC hybrid coating might be a general method for suppressing analyte adsorption and EOF in polymer MCE devices. The current MCE-based method might be a promising alternative for high-throughput screening of carbohydrate alterations in glycoproteins.

Analysis of amino acids and proteins using a poly(methyl methacrylate) microfluidic system

Plastic microchips are very promising analytical devices for the high-speed analysis of biological compounds. However, due to its hydrophobicity, their surface strongly interacts with nonpolar analytes or species containing hydrophobic domains, resulting in a significant uncontrolled adsorption on the channel walls. This paper describes the migration of fluorescence-labeled amino acids and proteins using the poly(methyl methacrylate) microchip. A cationic starch derivative significantly decreases the adsorption of analytes on the channel walls. The migration time of the analytes was related to their molecular weight and net charge or pI of the analytes. FITC-BSA migrated within 2 min, and the theoretical plate number of the peak reached 480,000 plates/m. Furthermore, proteins with a wide range of pI values and molecular weights migrated within 1 min using the microchip.

Replica multichannel polymer chips with a network of sacrificial channels sealed by adhesive printing method

Replica microchips for capillary array electrophoresis containing 10 separation channels (50 microm width, 50 microm depth and 100 microm pitch) and a network of sacrificial channels (100 microm width and 50 microm depth) were successfully fabricated on a poly(methyl methacrylate) (PMMA) substrate by injection molding. The strategy involved development of moving mask deep X-ray lithography to fabricate an array of channels with inclined channel sidewalls. A slight inclination of channel sidewalls, which can not be fabricated by conventional deep X-ray lithography, is highly required to ensure the release of replicated polymer chips from a mold. Moreover, the sealing of molded PMMA multichannel chips with a PMMA cover film was achieved by a novel bonding technique involving adhesive printing and a network of sacrificial channels. An adhesive printing process enables us to precisely control the thickness of an adhesive layer, and a network of sacrificial channels makes it possible to remove air bubbles and an excess adhesive, which are crucial to achieving perfect sealing of replica PMMA chips with well-defined channel and injection structures. A CCD camera equipped with an image intensifier was used to simultaneously monitor electrophoretic separations in ten micro-channels with laser-induced fluorescence detection. High-speed and high-throughput separations of a 100 bp DNA ladder and phi X174 Hae III DNA restriction fragments have been demonstrated using a 10-channel PMMA chip. The current work establishes the feasibility of mass production of PMMA multichannel chips at a cost-effective basis.

DNA damage induced by sulfite autoxidation catalyzed by copper(ii) tetraglycine complexes

Copper(II)/(III) tetraglycine complexes were investigated for their ability to catalyze the autoxidation of sulfite resulting in oxidative DNA damage. The focus of this work is on DNA damage by Cu(III) and oxysulfur radicals formed by the oxidation of S(IV) oxides by dissolved oxygen in the presence of Cu(II) tetraglycine complexes. The results suggest that sulfite is rapidly oxidized by oxygen in the presence of Cu(II) complexes producing Cu(III) tetraglycine, which can be monitored spectrophotometrically at 365 nm. A synergistic effect of Cu(II) with a second metal ion (Ni(II), Co(II) or Mn(II) traces) was observed.

Capillary columns in liquid chromatography: between conventional columns and microchips

Liquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations. The development of micro column separations in the early years has been described, starting with the papers of Horváth and co-workers and Ishii and co-workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small-bore columns. Based on internal diameters a classification of the different analytical HPLC columns has been suggested. The advantages of small-bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited. Open tubular columns are treated as a part of the historic background. The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two-dimensional comprehensive liquid chromatography. Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed.

Electrokinetically Controlled DNA Hybridization Microfluidic Chip Enabling Rapid Target Analysis

Biosensors and more specifically biochips exploit the interactions between a target analyte and an immobilized biological recognition element to produce a measurable signal. Systems based on surface nucleic acid hybridization, such as microarrays, are particularly attractive due to the high degree of selectivity in the binding interactions. One of the drawbacks of this reaction is the relatively long time required for complete hybridization to occur, which is often the result of diffusion-limited reaction kinetics. In this work, an electrokinetically controlled DNA hybridization microfluidic chip will be introduced. The electrokinetic delivery technique provides the ability to dispense controlled samples of nanoliter volumes directly to the hybridization array (thereby increasing the reaction rate) and rapidly remove nonspecific adsorption, enabling the hybridization, washing, and scanning procedures to be conducted simultaneously. The result is that all processes from sample dispensing to hybridization detection can be completed in as little as 5 min. The chip also demonstrates an efficient hybridization scheme in which the probe saturation level is reached very rapidly as the targets are transported over the immobilized probe site enabling quantitative analysis of the sample concentration. Detection levels as low as 50 pM have been recorded using an epifluorescence microscope.

Cationic Starch Derivatives as Dynamic Coating Additives for Analysis of Amino Acids and Peptides Using Poly(methyl methacrylate) Microfluidic Devices

Plastic microchips are very promising analytical devices because they are less fragile and are suitable for mass production. However, due to their hydrophobicity, the surface strongly interacts with nonpolar analytes or species containing hydrophobic domains, resulting in significant uncontrolled adsorption on channel walls. This paper describes the poly(methyl methacrylate) surface treatment by dynamic coating additives that considerably decreases adsorption of analytes to channel walls. Among the additives studied, quaternary ammonium starch derivatives suppressed the adsorption of fluorescently labeled amino acids and peptides most effectively. The effect was valid over the wide pH range from 2.5 to 8.0. Using a 10 mM phosphate buffer (pH 7.0) with 3% (w/v) quaternary ammonium starch as the running buffer, Asp and Glu, respectively, migrated at 54.6 and 57.6 s with efficiencies of 380 000 and 370 000 plates/m. In addition, this cationic starch derivative was found to possess good solubility and low viscosity.