Microchip isoelectric focusing using a miniature scanning detection system

Mobilization in two-step capillary isoelectric focusing: Concepts assessed by computer simulation

The mobilization step in a two-step capillary isoelectric focusing protocol is discussed by means of dynamic computer simulation data for systems without and with spacer compounds that establish their zones at the beginning and end of the focusing column. After focusing in an electroosmosis-free environment (first step), mobilization (second step) can be induced electrophoretically, by the application of a hydrodynamic flow, or by a combination of both means. Dynamic simulations provide insight into the complexity of the various modes of electrophoretic mobilization and dispersion associated with hydrodynamic mobilization. The data are discussed together with the relevant literature.

Review: Electric field driven pumping in microfluidic device

Pumping of fluids with precise control is one of the key components in a microfluidic device. The electric field has been used as one of the most popular and efficient nonmechanical pumping mechanism to transport fluids in microchannels from the very early stage of microfluidic technology development. This review presents fundamental physics and theories of the different microscale phenomena that arise due to the application of an electric field in fluids, which can be applied for pumping of fluids in microdevices. Specific mechanisms considered in this report are electroosmosis, AC electroosmosis, AC electrothermal, induced charge electroosmosis, traveling wave dielectrophoresis, and liquid dielectrophoresis. Each phenomenon is discussed systematically with theoretical rigor and role of relevant key parameters are identified for pumping in microdevices. We specifically discussed the electric field driven body force term for each phenomenon using generalized Maxwell stress tensor as well as simplified effective dipole moment based method. Both experimental and theoretical works by several researchers are highlighted in this article for each electric field driven pumping mechanism. The detailed understanding of these phenomena and relevant key parameters are critical for better utilization, modulation, and selection of appropriate phenomenon for efficient pumping in a specific microfluidic application.

Protein separation under a microfluidic regime

Lab-on-a-Chip (LoC), or micro-Total Analysis Systems (μTAS), is recognized as a powerful analytical technology with high capabilities, though end-user products for protein purification are still far from being available on the market. Remarkable progress has been achieved in the separation of nucleic acids and proteins using electrophoretic microfluidic devices, while pintsize devices have been developed for protein isolation according to miniaturized chromatography principles (size, charge, affinity, etc.). In this work, we review the latest advances in the fabrication of components, detection methods and commercial implementation for the separation of biological macromolecules based on microfluidic systems, with some critical remarks on the perspectives of their future development towards standardized microfluidic systems and protocols. An outlook on the current needs and future applications is also presented.

Reagent-release capillary array-isoelectric focusing device as a rapid screening device for IEF condition optimization

This report describes the fabrication and characterization of a simple and disposable capillary isoelectric focusing (cIEF) device containing a reagent-release capillary (RRC) array and poly(dimethylsiloxane) (PDMS) platform, which allows rapid (within 10 min) screening of cIEF conditions by introducing a sample solution into plural RRCs by capillary action followed by electric field application. To prepare the RRC, covalent immobilization of poly(dimethylacrylamide) (PDMA) was conducted to suppress electro-osmotic flow (EOF), followed by physical adsorption of the mixture of carrier ampholyte (CA), surfactant, labeling reagent (LR), and other additives to the PDMA surface to construct a two-layer structure inside a square glass capillary. When the sample solution containing proteins was introduced into the RRC, physically adsorbed CA, surfactant, and LR can be dissolved and released into the sample solution. Then, complexation of LR with proteins, mixing with CA and surfactant, and exposure of the PDMA surface spontaneously occurs for the IEF experiments. Here, three different RRCs that immobilize different CAs were prepared, and simultaneous cIEF experiments involving hemoglobin AFSC mixtures for choosing the best CA demonstrated the proof of concept.

Microchip DNA electrophoresis with automated whole-gel scanning detection

Gel electrophoresis continues to play an important role in miniaturized bioanalytical systems, both as a stand alone technique and as a key component of integrated lab-on-a-chip diagnostics. Most implementations of microchip electrophoresis employ finish-line detection methods whereby fluorescently labeled analytes are observed as they migrate past a fixed detection point near the end of the separation channel. But tradeoffs may exist between the simultaneous goals of maximizing resolution (normally achieved by using longer separation channels) and maximizing the size range of analytes that can be studied (where shorter separation distances reduce the time required for the slowest analytes to reach the detector). Here we show how the miniaturized format can offer new opportunities to employ alternative detection schemes that can help address these issues by introducing an automated whole-gel scanning detection system that enables the progress of microchip-based gel electrophoresis of DNA to be continuously monitored along an entire microchannel. This permits flexibility to selectively observe smaller faster moving fragments during the early stages of the separation before they have experienced significant diffusive broadening, while allowing the larger slower moving fragments to be observed later in the run when they can be better resolved but without the need for them to travel the entire length of the separation channel. Whole-gel scanning also provides a continuous and detailed picture of the electrophoresis process as it unfolds, allowing fundamental physical parameters associated with DNA migration phenomena (e.g., mobility, diffusive broadening) to be rapidly and accurately measured in a single experiment. These capabilities are challenging to implement using finish-line methods, and make it possible to envision a platform capable of enabling separation performance to be rapidly screened in a wide range of gel matrix materials and operating conditions, even allowing separation and matrix characterization steps to be performed simultaneously in a single self-calibrating experiment.

Recent progress of online sample preconcentration techniques in microchip electrophoresis

Microchip electrophoresis (MCE) has been advanced remarkably by the applications of several separation modes and the integration with several chemical operations on a single planer substrate. MCE shows superior analytical performance, e.g., high-speed analysis, high resolution, low consumption of reagents, and so on, whereas low-concentration sensitivity is still one of the major problems. To overcome this drawback, various online sample preconcentration techniques have been developed in MCE over the past 15 years, which have successfully enhanced the detection sensitivity in MCE. This review highlights recent developments in online sample preconcentration in MCE categorized on the basis of "dynamic" and "static" methods. The dynamic techniques including field amplified stacking, ITP, sweeping, and focusing have been easily applied to MCE, which provide effective enrichments of various analytes. The static techniques such as SPE and filtration have also been combined with MCE. In the static techniques, extremely high preconcentration efficiency can be obtained, compared to the dynamic methods. This review provides comprehensive tables listing the applications and sensitivity enhancement factors of these preconcentration techniques employed in MCE.

Multistage isoelectric focusing in a polymeric microfluidic chip

This paper reports a protocol that improves the resolving power of isoelectric focusing (IEF) in a polymeric microfluidic chip. This method couples several stages of IEF in series by first focusing proteins in a straight channel using broad-range ampholytes and then refocusing segments of the first channel into secondary channels that branch from the first one at T-junctions. Experiments demonstrate that several fluorescent proteins that had focused within a segment of the straight channel in the first stage were refocused at significantly higher resolution due to the shallower pH gradient and higher electrical field gradient. Two variants of green fluorescent protein from the second-stage IEF fractionation were further separated in a third stage. Three stages of IEF were completed in less than 25 min at electric field strengths ranging from 50 to 214 V/cm.

Effects of separation length and voltage on isoelectric focusing in a plastic microfluidic device

This paper describes the investigation on the effects of separation length and voltage on IEF in a plastic microfluidic device. A LIF, whole-channel imaging detection (WCID) system was developed to monitor proteins while they were moving under an electric field. IEF was carried out in a separation medium consisting of carrier ampholytes and a mixture of linear polymers (hydroxyethylcellulose and hydroxypropylcellulose). We found that the IEF separation resolution is essentially independent of separation length when the same voltage is applied, which agrees with the theory. This result supports the notion that IEF in a microfabricated device leads to more rapid analysis without sacrificing the resolving power. A higher separation voltage also brought about more rapid analysis and superior separation resolution. IEF of two proteins (green fluorescence protein and R-phycoerythrin) was achieved in 1.5 min when 500 V was applied across a 1.9-cm channel. We found that a linear relationship exists between the focusing time and the inverse of the electrical field strength. In addition, we confirmed the phenomenon in which the pH gradient was compressed to the middle of a channel, and we found that the relative amount of the gradient compression decreased with the channel length.

Low Viscous Separation Media for Genomics and Proteomics Analysis on Microchip Electrophoresis System

Microchip electrophoresis has widely grown during the past few years, and it has showed a significant result as a strong separation tool for genomic as well as proteomic researches. To enhance and expand the role of microchip electrophoresis, several studies have been proposed especially for the low viscous separation media, which is an important factor for the success of microchip with its narrow separation channels. In this paper we show an overview for the done researches in the field of low viscous media developed for the use in microchip electrophoresis. For genomic separation studies polyhydroxy additives have been used enhance the separation of DNA at low polymer concentration of HPMC (Hydroxypropylmethyl cellulose) which could keep the viscosity low. Mixtures of poly(ethylene oxide) as well as Hydroxyporpyl cellulose have been successfully introduced for chip separation. Furthermore high molecular mass polyacrylamides at low concentrations have been studied for DNA separation. A mixture of polymer nanoparticle with conventional polymers could show a better resolution for DNA at low concentration of the polymer. For the proteomic field isoelectric focusing on chip has been well overviewed since it is the most viscous separation media which is well used for the protein separation. The different types of isoelectric focusing such as the ampholyte-free type, the thermal type as well as the ampholyte-depended type have been introduced in this paper. Isoelectric focusing on chip with its combination with sodium dodecyl sulfate (SDS) page or free solution could give a better separation. Several application for this low viscous separation medias for either genomic or proteomic could clearly show the importance of this field.

Molecular diagnostics by microelectronic microchips

Molecular diagnostics is being revolutionized by the development of highly advanced technologies for DNA and RNA testing. One of the most important challenges is the integration of microelectronics to microchip-based nucleic acid technologies. The specific characteristics of these microsystems make the miniaturization and automation of any step of a molecular diagnostic procedure possible. This review describes the application of microelectronics to all the processes involved in a genetic test, particularly to sample preparation, DNA amplification and sequence variation detection.

Chemiluminescence micro-flow-injection analysis on a chip

Chemiluminescence microflow-injection analysis (microFIA) systems on a chip have been developed. The technology of laser ablation was used to fabricate the microchannels on the polymethyl methacrylate (PMMA) chip. The three sampling structure, including double-tee sampling structure, microvalve sampling structure and injection pump with accurate time control, were used. The microcolumn for specific molecular recognition, including molecularly imprinted polymer, enzyme and bacteria, were used to enhance selectivity. These microFIA systems have been applied to clinical analysis, assessment of food safety, in vivo and real-time determination of drugs, and pharmacokinetics studies.

Human genomic DNA analysis using a semi-automated sample preparation, amplification, and electrophoresis separation platform

The growing importance of analyzing the human genome to detect hereditary and infectious diseases associated with specific DNA sequences has motivated us to develop automated devices to integrate sample preparation, real-time PCR, and microchannel electrophoresis (MCE). In this report, we present results from an optimized compact system capable of processing a raw sample of blood, extracting the DNA, and performing a multiplexed PCR reaction. Finally, an innovative electrophoretic separation was performed on the post-PCR products using a unique MCE system. The sample preparation system extracted and lysed white blood cells (WBC) from whole blood, producing DNA of sufficient quantity and quality for a polymerase chain reaction (PCR). Separation of multiple amplicons was achieved in a microfabricated channel 30 microm x 100 microm in cross section and 85 mm in length filled with a replaceable methyl cellulose matrix operated under denaturing conditions at 50 degrees C. By incorporating fluorescent-labeled primers in the PCR, the amplicons were identified by a two-color (multiplexed) fluorescence detection system. Two base-pair resolution of single-stranded DNA (PCR products) was achieved. We believe that this integrated system provides a unique solution for DNA analysis.

Comparison of the performance characteristics of poly(dimethylsiloxane) and Pyrex microchip electrophoresis devices for peptide separations

A comparative study of electrophoretic separations of fluorescently labeled peptides and amino acids on poly(dimethylsiloxane) (PDMS) and Pyrex microchips is presented. The separation parameters for each microchip substrate were compared, including electroosmotic flow, plate numbers, resolution, and limits of detection. The effect of buffer composition on the separation was also investigated. Acceptable separations were obtained for most peptides with both substrates; however, PDMS chips exhibited much lower separation efficiencies and longer analysis times.

On-chip coupling of isoelectric focusing and free solution electrophoresis for multidimensional separations

We have developed an acrylic microfluidic device that sequentially couples liquid-phase isoelectric focusing (IEF) and free solution capillary electrophoresis (CE). Rapid separation (<1 min) and preconcentration (73x) of species were achieved in the initial IEF dimension. Using full-field fluorescence imaging, we observed nondispersive mobilization velocities on the order of 20 microm/s during characterization of the IEF step. This transport behavior allowed controlled electrokinetic mobilization of focused sample bands to a channel junction, where voltage switching was used to repeatedly inject effluent from the IEF dimension into an ampholyte-based CE separation. This second dimension was capable of analyzing all fluid volumes of interest from the IEF dimension, as IEF was 'parked' during each CE analysis and refocused prior to additional CE analyses. Investigation of each dimension of the integrated system showed time-dependent species displacement and band-broadening behavior consistent with IEF and CE, respectively. The peak capacity of the 2D system was approximately 1300. A comprehensive 2D analysis of a fluid volume spanning 15% of the total IEF channel length was completed in less than 5 min.

Electrokinetic transport of red blood cells in microcapillaries

Electrokinetic flow of a suspension of erythrocytes (red blood cells, RBCs) in 20 num cylindrical fused-silica capillaries is examined in the present work. Flow direction anomalies are observed experimentally and tentatively explained by the development of a pH gradient between the cathode well and the anode well due to electrolysis reactions at the electrodes. This pH gradient alters the local zeta potentials of both the capillary and the RBC and thus the local electroendosmotic liquid flow (EOF) velocities and RBC electrophoretic (EP) velocities. The two velocities are opposite in direction but with EOF dominating such that the RBC moves toward the cathode, opposite to the anode migration observed in bulk conditions. The opposing zeta potentials also lead to RBC aggregation at the anode end for low fields less than 25 V/cm. As the electroendosmotic velocity decreases at the anode end due to decreasing pH, pressure-driven back flow develops to oppose the original EOF at the remaining portions of the capillary ensuring constant fluid flux. When the anode EOF velocity is smaller in magnitude than the EP velocity, reversal of blood cell transport is observed after a short transient time in which a pH gradient forms. RBC velocities and pH dependencies on electric field and MgCl(2) concentration are presented along with data showing the accumulation of charge separation across the capillary. Also, a short-term solution to the pH gradient formation is presented that could help thwart development of pH gradients in micro-devices at lower voltages.

Microfluidic chips for clinical and forensic analysis

This review gives an overview of developments in the field of microchip analysis for clinical diagnostic and forensic applications. The approach chosen to review the literature is different from that in most microchip reviews to date, in that the information is presented in terms of analytes tested rather than microchip method. Analyte categories for which examples are presented include (i) drugs (quality control, seizures) and explosives residues, (ii) drugs and endogenous small molecules and ions in biofluids, (iii) proteins and peptides, and (iv) analysis of nucleic acids and oligonucleotides. Few cases of microchip analysis of physiological samples or other "real-world" matrices were found. However, many of the examples presented have potential application for these samples, especially with ongoing parallel developments involving integration of sample pretreatment onto chips and the use of fluid propulsion mechanisms other than electrokinetic pumping.

Lab-on-a-chip: applications in proteomics

Recent advances in chip-based separation of proteins provide methods that are faster and more convenient than conventional gel electrophoresis. Rapid and automated protein sizing on a chip is at the commercial stage and first attempts have been made to perform two-dimensional separation on a chip. Numerous designs have been described to interface a microfluidic chip to a mass spectrometer. Impressive integration efforts are demonstrated by the ability to perform on-chip trypsin digestion, separation and injection into a mass spectrometer with a single device.