Protein analysis of an individual Caenorhabditis elegans single-cell embryo by capillary electrophoresis

Gold-coated polydimethylsiloxane microwells for high-throughput electrochemiluminescence analysis of intracellular glucose at single cells

In this communication, a gold-coated polydimethylsiloxane (PDMS) chip with cell-sized microwells was prepared through a stamping and spraying process that was applied directly for high-throughput electrochemiluminescence (ECL) analysis of intracellular glucose at single cells. As compared with the previous multiple-step fabrication of photoresist-based microwells on the electrode, the preparation process is simple and offers fresh electrode surface for higher luminescence intensity. More luminescence intensity was recorded from cell-retained microwells than that at the planar region among the microwells that was correlated with the content of intracellular glucose. The successful monitoring of intracellular glucose at single cells using this PDMS chip will provide an alternative strategy for high-throughput single-cell analysis. Graphical abstract ᅟ.

Protein fingerprinting of Staphylococcus aureus by capillary electrophoresis with on-capillary derivatization and laser-induced fluorescence detection

This chapter describes a complete procedure for obtaining protein fingerprints of microorganisms using capillary electrophoresis (CE) with laser-induced fluorescence detection (LIF). Staphylococcus aureus, a human pathogen responsible of frequent and resistant infections, is used as model microorganism to show the feasibility of this procedure. Bacteria are grown in different culture media or submitted to temperature or nitrosative stress conditions. After the growth of the bacteria, the protein extracts are obtained by cell lysis using sonication. The water-soluble fraction of these lysates is derivatized on-capillary with the fluorogenic reagent 3-(2-furoyl)quinoline-2-carboxaldehyde. The fluorescent products are analyzed by CE and detected by LIF. Practical advices for the interpretation of the electropherograms are given. To do so, the variations of the protein fingerprints of the bacteria with the culture conditions, such as growth medium, or the stressing conditions, such as heat shock or nitrosative stress, are used as example.

Interface of an array of five capillaries with an array of one-nanoliter wells for high-resolution electrophoretic analysis as an approach to high-throughput chemical cytometry

We report a system that allows the simultaneous aspiration of one or more cells into each of five capillaries for electrophoresis analysis. A glass wafer was etched to create an array of 1-nL wells. The glass was treated with poly(2-hydroxyethyl methacrylate) to control cell adherence. A suspension of formalin-fixed cells was placed on the surface, and cells were allowed to settle. The concentration of cells and the settling time were chosen so that there was, on average, one cell per well. Next, an array of five capillaries was placed so that the tip of each capillary was in contact with a single well. A pulse of vacuum was applied to the distal end of the capillaries to aspirate the content of each well into a capillary. Next, the tips of the capillaries were placed in running buffer and potential was applied. The cells lysed upon contact with the running buffer, and fluorescent components were detected at the distal end of the capillaries by laser-induced fluorescence. The electrophoretic separation efficiency was outstanding, generating over 750,000 theoretical plates (1,800,000 plates/m). In this example, AtT-20 cells were used that had been treated with TMR-G(M1). The cells were allowed to metabolize this substrate into a series of products before the cells were fixed. The number of cells found in each well was estimated visually under the microscope and was described by a Poisson distribution with mean of 0.98 cell/well. This system provides an approach to high-throughput chemical cytometry.

Characterizing intercellular signaling peptides in drug addiction

Intercellular signaling peptides (SPs) coordinate the activity of cells and influence organism behavior. SPs, a chemically and structurally diverse group of compounds responsible for transferring information between neurons, are broadly involved in neural plasticity, learning and memory, as well as in drug addiction phenomena. Historically, SP discovery and characterization has tracked advances in measurement capabilities. Today, a suite of analytical technologies is available to investigate individual SPs, as well as entire intercellular signaling complements, in samples ranging from individual cells to entire organisms. Immunochemistry and in situ hybridization are commonly used for following preselected SPs. Discovery-type investigations targeting the transcriptome and proteome are accomplished using high-throughput characterization technologies such as microarrays and mass spectrometry. By integrating directed approaches with discovery approaches, multiplatform studies fill critical gaps in our knowledge of drug-induced alterations in intercellular signaling. Throughout the past 35 years, the National Institute on Drug Abuse has made significant resources available to scientists that study the mechanisms of drug addiction. The roles of SPs in the addiction process are highlighted, as are the analytical approaches used to detect and characterize them.

Fast-lysis cell traps for chemical cytometry

Electrically addressable cell traps were integrated with capillary electrophoresis for the analysis of the contents of single adherent cells. Electrodes composed of indium tin oxide were patterned on a glass surface followed by formation of topographical cell traps using 1002F photoresist. Single cells trapped in the holes could be lysed in less than 66 ms by applying a brief electric field (10 ms) across the electrode beneath the cell and the ground electrode placed in the aqueous media above the cell traps. The gas formed during cell lysis remained localized within the cavity formed by the 1002F photoresist. The retention of the gas in the cell trap enabled the cell traps to be coupled to an overlying capillary without blockage of the capillary. Single cells cultured in the traps were loaded with fluorescein and Oregon Green and then electrically lysed. By simultaneous application of an electric field to the capillary, the cell's contents were loaded into the capillary and electrophoretically separated. Orgeon Green and fluorescein from a single cell were fully resolved in less than two minutes. The use of a single patterned electrode beneath the 1002F cell trap yielded a simple easily fabricated design that was robust when immersed in aqueous solutions. Moreover, the design can easily be scaled up to create arrays of adherent cells for serial analyses using a single capillary or for parallel analysis by mating to an array of capillaries. Enhancing the rate of analysis of single adherent cells would enable a greater understanding of cellular physiology.

Chemical analysis of single cells

Chemical analysis of single cells requires methods for quickly and quantitatively detecting a diverse array of analytes from extremely small volumes (femtoliters to nanoliters) with very high sensitivity and selectivity. Microelectrophoretic separations, using both traditional capillary electrophoresis and emerging microfluidic methods, are well suited for handling the unique size of single cells and limited numbers of intracellular molecules. Numerous analytes, ranging from small molecules such as amino acids and neurotransmitters to large proteins and subcellular organelles, have been quantified in single cells using microelectrophoretic separation techniques. Microseparation techniques, coupled to varying detection schemes including absorbance and fluorescence detection, electrochemical detection, and mass spectrometry, have allowed researchers to examine a number of processes inside single cells. This review also touches on a promising direction in single cell cytometry: the development of microfluidics for integrated cellular manipulation, chemical processing, and separation of cellular contents.

Chemical cytometry: fluorescence-based single-cell analysis

Cytometry deals with the analysis of the composition of single cells. Flow and image cytometry employ antibody-based stains to characterize a handful of components in single cells. Chemical cytometry, in contrast, employs a suite of powerful analytical tools to characterize a large number of components. Tools have been developed to characterize nucleic acids, proteins, and metabolites in single cells. Whereas nucleic acid analysis employs powerful polymerase chain reaction-based amplification techniques, protein and metabolite analysis tends to employ capillary electrophoresis separation and ultrasensitive laser-induced fluorescence detection. It is now possible to detect yoctomole amounts of many analytes in single cells.

Coaxial flow system for chemical cytometry

Over the past decade, chemical cytometry performed by capillary electrophoresis (CE) has become increasingly valuable as a bioanalytical tool to quantify analytes from single cells. However, extensive use of CE-based chemical cytometry has been hindered by the relatively low throughput for the analysis of single adherent cells. In order to overcome the low throughput of CE-based analysis of adherent cells and increase its utility in evaluating cellular attributes, new higher throughput methods are needed. Integration of a coaxial buffer exchange system with CE-based chemical cytometry increased the rate of serial analyses of cells. In the designed system, fluid flow through a tube coaxial to the separation capillary was used to supply electrophoretic buffer to the capillary. This sheath or coaxial fluid was turned off between analysis of cells and on during cell sampling and electrophoresis. Thus, living cells were not exposed to the nonphysiologic electrophoretic buffer prior to lysis. Key parameters of the system such as the relative capillary-sheath positions, buffer flow velocities, and the cell chamber design were optimized. To demonstrate the utility of the system, rat basophilic leukemic cells loaded with Oregon green and fluorescein were serially lysed and loaded into a capillary. Separation of the contents of 20 cells at a rate of 0.5 cells/min was demonstrated.

Cell cycle-dependent characterization of single MCF-7 breast cancer cells by 2-D CE

The composition of single MCF-7 breast cancer cells is characterized using 2-D CE. Individual MCF-7 cells were aspirated into a 30 mum inner diameter fused-silica capillary and lysed by contact with an SDS-containing buffer. Proteins and other primary amines were fluorescently labeled on-column using the fluorogenic dye 3-(2-furoyl)quinoline-2-carboxaldehyde. Labeled components were separated first according to molecular weight using capillary sieving electrophoresis (CSE) and then by MEKC. Analytes were detected in a sheath-flow cuvette using LIF. The expression profiles for MCF-7 cellular homogenate and a single MCF-7 cell are compared. As a proof-of-principle investigation, variation in expression was also compared within and between G1 and G2/M cell cycle phases for MCF-7 cells. Following their treatment with the viable nuclear stain Hoechst 33342, MCF-7 cells were sorted by flow cytometry on the basis of their ploidy. Sorted cells were then analyzed by 2-D CE. The degree of variability was >2.5 times larger between cells of different phases than between cells of the same phase. In typical 1 h 2-D CE separations using MCF-7 cells, over 100 components are resolved.

Repeatability of chemical cytometry: 2-DE analysis of single RAW 264.7 macrophage cells

This report presents the use of 2-DE with ultrasensitive fluorescence detection as a chemical cytometry tool to characterize the protein and biogenic amine content of single cells from the RAW 264.7 murine macrophage cell line. Cells were sorted by cell cycle prior to 2-DE analysis. Cells in the G2/M phase of the cell cycle were aspirated into the first-dimensional capillary and lysed. The cellular contents were fluorescently labeled and first separated by capillary sieving electrophoresis (CSE). Over 380 fractions were transferred from the first-dimensional capillary to the second-dimensional capillary, where components were further separated by MEKC and detected by laser-induced fluorescence. Twenty-five spots common to the four electropherograms were fit with a 2-D Gaussian surface to determine spot position, width, and amplitude. The RSD in CSE mobility was 1.0 +/- 0.6%. The mean uncertainty in spot position was 1.3 times larger than the mean spot width in the CSE dimension. The average SD in MEKC migration time was 0.37 +/- 0.13 s, which is smaller than the average spot size in this dimension. Spot capacity was 200. The RSD in spot amplitude was 50%, reflecting a large cell-to-cell variation in component expression.

Competitive immunoassay for clenbuterol using capillary electrophoresis with laser-induced fluorescence detection

A competitive immunoassay for detecting clenbuterol in urine was established by capillary electrophoresis (CE) with laser-induced fluorescence (LIF). The clenbuterol was conjugated with bovine serum albumin (BSA), and then the derivative was labeled with fluorescein isothiocyanate (FITC) and competes for antibody with free clenbuterol in the sample. Under the optimal conditions, Free and bound FITC labeled clenbuterol was separated within 8 min with the relative standard deviation (R.S.D.) 0.72% for migration time and 2.8% for peak area. The detection limit reached 0.7 ng/ml.

Single-cell protein analysis of a single mouse embryo by two-dimensional capillary electrophoresis

The characterization of protein expression from a single-cell mouse embryo using two-dimensional capillary electrophoresis (2D-CE) is described. These zygotes were obtained from Hsf1 gene knockout mice. Single zygotes were lysed off-column and proteins were fluorescently labeled using the fluorogenic dye 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ). After injection, analytes were separated first according to molecular weight using capillary sieving electrophoresis (CSE) and then by micellar electrokinetic capillary chromatography (MEKC) to obtain protein expression fingerprints. Analytes were detected in a sheath flow cuvette using laser-induced fluorescence. In a 1-h 2D-CE separation, over 100 components were resolved with a spot capacity of 380.

Capillary electrophoresis at the omics level: Towards systems biology

Emerging systems biology aims at integrating the enormous amount of existing omics data in order to better understand their functional relationships at a whole systems level. These huge datasets can be obtained through advances in high-throughput, sensitive, precise, and accurate analytical instrumentation and technological innovation. Separation sciences play an important role in revealing biological processes at various omic levels. From the perspective of systems biology, CE is a strong candidate for high-throughput, sensitive data generation which is capable of tackling the challenges in acquiring qualitative and quantitative knowledge through a system-level study. This review focuses on the applicability of CE to systems-based analytical data at the genomic, transcriptomic, proteomic, and metabolomic levels.

Laser-induced fluorescence detection schemes for the analysis of proteins and peptides using capillary electrophoresis

Over the past few years, a large number of studies have been prepared that describe the analysis of peptides and proteins using capillary electrophoresis (CE) and laser-induced fluorescence (LIF). These studies have focused on two general goals: (i) development of automatic, selective and quick separation and detection of mixtures of peptides or proteins; (ii) generation of new methods of quantitation for very low concentrations (nm and subnanomolar) of peptides. These two goals are attained with the use of covalent labelling reactions using a variety of dyes that can be readily excited by the radiation from a commonly available laser or via the use of noncovalent labelling (immunoassay using a labelled antibody or antigen or noncovalent dye interactions). In this review article, we summarize the works which were performed for protein and peptide analysis via CE-LIF.

Sample preparation for peptides and proteins in biological matrices prior to liquid chromatography and capillary zone electrophoresis

The determination of peptides and proteins in a biological matrix normally includes a sample-preparation step to obtain a sample that can be injected into a separation system in such a way that peptides and proteins of interest can be determined qualitatively and/or quantitatively. This can be a rather challenging, labourious and/or time-consuming process. The extract obtained after sample preparation is further separated using a compatible separation system. Liquid chromatography (LC) is the generally applied technique for this purpose, but capillary zone electrophoresis (CZE) is an alternative, providing fast, versatile and efficient separations. In this review, the recent developments in the combination of sample-preparation procedures with LC and CZE, for the determination of peptides and proteins, will be discussed. Emphasis will be on purification from and determination in complex biological matrices (plasma, cell lysates, etc.) of these compounds and little attention will be paid to the proteomics area. Additional focus will be put on sample-preparation conditions, which can be 'hard' or 'soft', and on selectivity issues. Selectivity issues will be addressed in combination with the used separation technique and a comparison between LC and CZE will be made.

Microfluidic devices for the high-throughput chemical analysis of cells

A microfluidic device is reported that integrated cell handling, rapid cell lysis, and electrophoretic separation and detection of fluorescent cytosolic dyes. The device function was demonstrated using Jurkat cells that were loaded with the fluorogenic dyes - carboxyfluorescein diacetate, Oregon green carboxylic acid diacetate, or Calcein AM. The loaded cells were hydrodynamically transported from the cell-containing reservoir to a region on the microfluidic device where they were focused and then rapidly lysed using an electric field. Complete lysis was accomplished in <33 ms. The hydrolyzed, fluorescent dyes in the cell lysate were automatically injected into a separation channel on the device and detected 3 mm downstream of the injection point. The total separation time was approximately 2.2 s with absolute migration time reproducibilities of <1% and efficiencies ranging from 2300 to 4000 theoretical plates. Results from 139 cells are reported. A small fraction of these cells, approximately 9%, were found to enzymatically hydrolyze the loaded dyes in a manner significantly different from the majority of the cells. Cell analysis rates of 7-12 cells/min were demonstrated and are >100 times faster than those reported using standard bench-scale capillary electrophoresis.

Capillary sodium dodecyl sulfate-DALT electrophoresis with laser-induced fluorescence detection for size-based analysis of proteins in human colon cancer cells

Capillary sodium dodecyl sulfate (SDS)-DALT electrophoresis (SDS-DALT-CE) refers to CE separation of proteins based on their size; DALT is the abbreviation for Dalton, the unit used to describe molecular weight. In this work, seven proteins from 18 to 116 kDa were denatured by SDS, labeled by 3-(2-furoyl) quinoline-2-carboxaldehyde, separated by SDS-DALT-CE in polyethylene oxide sieving matrix, and detected by laser-induced fluorescence (LIF) in a sheath flow cuvette. This method was combined with detergent differential fractionation, which is a protein fractionation method using a series of detergent-containing buffers to sequentially extract protein fractions from cells, to analyze the proteins in HT29 human colon adenocarcinoma cells. In addition, on-column labeling was demonstrated for protein analysis by SDS-DALT-CE with LIF, and applied to analysis of proteins in a single HT29 cancer cell. Most proteins had molecular masses from 10 to 120 kDa. Similar protein profiles were obtained for single cells and protein extract of a large cell population.

Capillary electrophoresis of proteins 1999-2001

This review article with 223 references describes recent developments in capillary electrophoresis (CE) of proteins and covers papers published during last two years, from the previous review (V. Dolnik, Electrophoresis 1999, 20, 3106-3115) through Spring 2001. It describes the topics related to CE of proteins including modeling of the electrophoretic properties of proteins, sample pretreatment, wall coatings, improving selectivity, detection, special electrophoretic techniques, and applications.

Capillary sodium dodecyl sulfate-DALT electrophoresis of proteins in a single human cancer cell

Capillary Sodium dodlecyl sulfate (SDS)-DALT an (abbreviation for Dalton) electrophoresis was applied to analysis of proteins in single HT29 human colon adenocarcinoma cells. A vacuum pulse was employed to introduce a single cell into the coated capillary. Once the cell was lysed, proteins were denatured with SDS, fluorescantly labeled with 3-(2-furoyl)-quinoline-2-carboxaldehyde (FQ), and then separated by using 8% pullulan as the sieving matrix. This method offers a few advantages for single-cell protein analysis. First, it provides reproducible separation of single-cell proteins according to their size. Based on comparison with the migration time of standard proteins, most components from a single HT29 cancer cell have molecular masses within the range of 10-100 kDa. Second, as a one-dimensional separation method, it gives fairly good resolution for proteins. Typically, around 30 protein components of a single HT29 cell were resolved, indicating that this method has similar peak capacity to SDS-polyacrylamide gel electrophoresis (PAGE). Third, this method shows high detection sensitivity and wide dynamic range, which is important because of the wide range of protein expression in living systems. Detection limits for standard proteins ranged from 10(-10) to 10(-11) M. Finally, this method provides much higher speed than classical gel electrophoresis methods, and it provides automated anlysis of cellular proteins at the single-cell level; the separation is complete in 30 min and the entire analysis takes approximately 45 min.