Capillary Electrophoresis as a Second Dimension to Isoelectric Focusing for Peptide Separation

Capillary zone electrophoresis and carrier ampholytes based capillary electrophoresis have been used as a second separation step to Off-Gel isoelectric focusing for the analysis of complex peptide mixtures. A tryptic digest of four proteins (bovine serum albumin, β-lactoglobulin, horse myoglobin, cytochrome c) has been chosen as a peptide test mixture. After assessment of different modes of capillary electrophoresis as a second dimension to Off-Gel isoelectric focusing, the optimized two-dimensional platforms provide a degree of orthogonality comparable to state-of-the-art multidimensional liquid chromatography systems as well as a practical peak capacity above 700

Electrokinetic supercharging for highly efficient peptide preconcentration in capillary zone electrophoresis

Electrokinetic supercharging has been integrated in CZE for the development of a highly sensitive methodology for protein tryptic digest analysis. A careful choice of the experimental conditions led to sensitivity enhancement factors between 1000 and 10 000 whilst maintaining a satisfactory resolution. Peptides in the low nanomolar concentration range have been detected despite the use of the poorly sensitive UV absorbance detection mode. The buffer system used in this study is fully suitable for coupling CE to MS

Iontophoretic Fraction Collection for Coupling Capillary Zone Electrophoresis with Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

An automated fraction collection interface has been developed for coupling capillary electrophoresis (CE) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). This fraction collection approach is based on electromigration and diffusion and does not rely on the presence of a liquid junction, sheath-liquid, electro-osmotic flow, or a superimposed hydrodynamic flow. Neutrally coated capillary with negligible electroosmosis can thus be used to provide high-efficiency separations of biological compounds. The in-capillary separation resolution is totally independent from the spotting process. CE-separated species can be collected either in a multiwell plate or directly on a MALDI target. In the present work, an eight-protein mixture, submitted to trypsin proteolysis, has been used as a sample test and separations have been conducted in 50 μm i.d. neutrally coated capillaries. As compared to direct MALDI MS analysis, the integration of CE improved the number of detected peptides from 36 to 87 and the average sequence coverage from 24% to 38%. Internal calibration was used, and an average mass accuracy of 16.1 ppm is reported. Finally, diffusion-migration numerical simulations of the iontophoretic fraction collection process have been carried out

Adsorbed protein detection by scanning electrochemical microscopy

A scanning electrochemical microscopy (SECM) protein detection methodology has been developed based on the tagging of free cysteines and other nucleophiles in proteins and peptides by benzoquinone. The tagged proteins are detected by the mediated reduction of benzoquinone with a redox species produced electrochemically at the SECM tip. After careful optimization, a sensitivity in the low ng mm 2 range was reached for bovine serum albumin. One of the major advantages of the present technique is that the selectivity of the protein tagging can be tuned by changing the pH of the reaction media. Depending on the requirements, cysteine selective or general detection can therefore be achieved with a high sensitivity. As a proof of concept, this technique was applied to the detection of protein spots and to the imaging of human fingerprints and further compared to the actual SECM state-of-art approach

In-source photocatalytic reduction of disulfide bonds during laser desorption ionization

A photosensitive plate based on sintered TiO2 nanoparticles has been developed to carry out in-source photo-induced reductions for cleavage of disulfide bridges using glucose as a hole scavenger during laser desorption ionization

Magnetic Beads Based Immunoaffinity Capillary Electrophoresis of Total Serum IgE with Laser-Induced Fluorescence Detection

A magnetic beads based immunoaffinity capillary electrophoresis method for total Immunoglobulin E quantification in serum has been developed. The method combines speed, automation ability, and minimal sample consumption. Only 1 μL of serum is required while the whole immunoaffinity capillary electrophoresis method is performed in less than 50 min. The concomitant use of online immunocapture, transient isotachophoresis, and laserinduced fluorescence detection provides a sensitivity in the low picomolar range and a highly linear fluorescence response over 4 orders of magnitude (IgE concentration ranging from 2.4 to 2400 ng/mL). After validation with a reference material, the method has been successfully applied to the quantification of total IgEs in patient sera. The results compared well with classical ImmunoCap data

Photocatalytic Redox Reactions for In-Source Peptide Fragmentation

In-source photocatalytic redox reactions based on a photosensitive target plate have been developed to realize peptide fragmentation during laser desorption ionization. Sample peptides and glucose are simply deposited on a spot of sintered TiO2 nanoparticles. With the irradiation of UV laser on TiO2, electrons are excited from the valence to the conduction band, leaving oxidative holes and reductive electrons to drive various insource redox reactions. Glucose, working here as a hole scavenger and conductor, can favor both on-surface reduction and long distance in-plume oxidation, therefore inducing peptide fragmentation. Ca-C backbone cleavage was observed to generate a,x fragment decay, while the N-Ca bond cleavage was also sometimes obtained to induce c,z fragmentation, but was rather weaker. The former dissociation is believed to originate from oxidative routes induced by the valence band holes, based on the oxidation of nitrogen atom at the peptide backbone, including hydrogen-radical abstraction and electron transfer. In contrast, the latter dissociation is supposed to be the result of reductive processes by the conduction band electrons, which are then rather similar to electron capture dissociation in tandem mass spectrometry

TiO2 Printed Aluminum Foil: Single-Use Film for a Laser Desorption/Ionization Target Plate

Single-use aluminum foil-based laser desorption/ionization (LDI) target plates have been developed for mass spectrometry (MS) analysis and provide detection results comparable to those of commercial stainless steel plates while offering a convenient way to avoid the time-consuming surface cleaning process. Additionally, arrays of TiO2 nanoparticle spots are coated on the foil either by screen-printing or rotogravure-printing followed by sintering to form a mesoporous layer spot to act as an anchor for sample deposition. These TiO2 spots offer further functions to the Al foil, such as matrix-free laser desorption/ionization or specific affinity for in situ enrichment of phosphopeptides. The single-use TiO2-Al foils are cheap to produce, easy to use, and well suited for high-throughput proteomics research. They can also be of interest for protein post-translational modifications study

Magnetic forces produced by rectangular permanent magnets in static microsystems

Finite element numerical simulations were carried out in 2D geometries to map the magnetic field and force distribution produced by rectangular permanent magnets as a function of their size and position with respect to a microchannel. A single magnet, two magnets placed in attraction and in repulsion have been considered. The goal of this work is to show where magnetic beads are preferentially captured in a microchannel. These simulations were qualitatively corroborated, in one geometrical case, by microscopic visualizations of magnetic bead plug formation in a capillary. The results show that the number of plugs is configuration dependent with: in attraction, one plug in the middle of the magnets; in repulsion, two plugs near the edges of the magnets; and with a single magnet, a plug close to the center of the magnet. The geometry of the magnets (h and l are the height and length of the magnets respectively) and their relative spacing s has a significant impact on the magnetic flux density. Its value inside a magnet increases with the h/l ratio. Consequently, bar magnets produce larger and more uniform values than flat magnets. The l/s ratio also influences the magnetic force value in the microchannel, both increasing concomitantly for all the configurations. In addition, a zero force zone in the middle appears in the attraction configuration as the l/s ratio increases, while with a single magnet, the number of maxima and minima goes from one to two, producing two focusing zones instead of only one