Capillary Interface Research Articles

Genetic markers and their influence on cerebrovascular malformations.

Cerebrospinal vascular malformations are a group of anomalies affecting the arterial wall, the capillary arteriovenous interface, or the venous and lymphatic structures. Heritability and family studies allow identification of mutations in single genes associated with rare familial conditions causing cerebral or spinal vascular malformations, as is the case in hemorrhagic hereditary telangiectasia diseases. This article reviews the genetic and epigenetic influences increasingly reported in recent years as causal factors or triggers involved in the formation and growth of cerebromedullary vascular malformations.

A field-portable membrane introduction mass spectrometer for real-time quantitation and spatial mapping of atmospheric and aqueous contaminants.

Environmental concentrations of volatile and semivolatile organic compounds (VOC/SVOCs) can vary dramatically in time and space under the influence of environmental conditions. In an industrial setting, multiple point and diffuse sources can contribute to fugitive emissions. Assessments and monitoring programs using periodic grab sampling provide limited information, often with delay times of days or weeks. We report the development and use of a novel, portable membrane introduction mass spectrometry (MIMS) system capable of resolving and quantifying VOC and SVOCs with high spatial and temporal resolution, in the field, in real-time. An electron impact ionization cylindrical ion trap mass spectrometer modified with a capillary hollow fiber polydimethylsiloxane membrane interface was used for continuous air and water sampling. Tandem mass spectrometry and selected ion monitoring scans performed in series allowed for the quantitation of target analytes, and full scan mode was used to survey for unexpected analytes. Predeployment and in-field external calibrations were combined with a continuously infused internal standard to enable real-time quantitation and monitor instrument performance. The system was operated in a moving vehicle with internet-linked data processing and storage. Software development to integrate MIMS and relevant meta-data for visualization and geospatial presentation in Google Earth is presented. Continuous quantitation enables the capture of transient events that may be missed or under-represented by traditional grab sampling strategies. Real-time geospatial maps of chemical concentration enable adaptive sampling and in-field decision support. Sample datasets presented in this work were collected in Northern Alberta in 2010-2012.

Interview with Donald E Ingber.

Interview with Donald E Ingber.

Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures

Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of nine peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN compared with using the standard atmospheric pressure single ESI emitter/heated capillary interface.

Microfluidic PMMA interfaces for rectangular glass capillaries

We present the design and fabrication of a polymeric capillary fluidic interface fabricated by micro-milling. The design enables the use of glass capillaries with any kind of cross-section in complex microfluidic setups. We demonstrate two different designs of the interface; a double-inlet interface for hydrodynamic focusing and a capillary interface with integrated pneumatic valves. Both capillary interfaces are presented together with examples of practical applications. This communication shows the design optimization and presents details of the fabrication process. The capillary interface opens up for the use of complex microfluidic systems in single-use glass capillaries. They also enable simple fabrication of glass/polymer hybrid devices that can be beneficial in many research fields where a pure polymer chip negatively affects the device's performance, e.g. acoustofluidics.

On the reliability of mathematical modelling of capillary barriers

The problem of the reliability of capillary-barriers' modelling is studied making use of tipping trough measurements. In its fi rst part, the article describes laboratory mea surements of saturated hydraulic conductivities and retention curves of four materials of two different capillary barriers. Both the main branches of the retention curves were measured, and the unsaturated hydraulic conductivities and capacity functions were determined. The second part of the article describes numerical modelling of two tipping trough experiments. The obtained results are compared with the measured data. The comparison shows a good agreement that is presented and discussed. It is concluded that, in the case of capillary barrier materials, the laboratory measurements made on samples and the subsequent math- ematical modelling can substitute for the tipping trough experiments. The capillary barrier is a simple device frequently used to cover landfi lls. It consists of two inclined layers: the overlying fi ne grained layer called the capillary layer and the underlying coarse grained layer called the capillary block. The capillary layer consists of fimaterial, usually a fi ne to medium grained sand, while the capillary block consists of signifi cantly coarser material usually a uniform coarse-grained sand or figravel. The insulating effect of the barrier is based on the fact that, under suffi ciently low values of pressure head, the hydraulic conductivity of the upper layer is signifi cantly, at least one order, higher than that of the capillary block. The infi ltrating water comes from above into the capillary layer and fl ows along it downwards rather than to cross the interface (the capillary interface) and to enter the capillary block, see e.g. Ross (1) or Abdolahzadeh et al. (2). Several laboratory experiments testing two capillary barriers were carried out at the Ruhr University in Bochum. A large tipping trough containing the barriers was used for the exper- iments (3). A measured time-dependent infi ltration into the capillary layer was applied and the responding discharge from both layers of the tested barriers was measured as a function of time. The results made it possible to fi nd out critical values of infi ltration intensity and cumulative infi ltration causing water fl ow through the capillary interface into the capil- lary block (3) and (4). The tested barriers were built up of well-defi ned standard materials and, moreover, several physical characteristics of the materials were measured in Bochum. Numerical simulations of water behaviour in capillary barriers are based on numerical solutions of the Richards equation describing water fl ow in unsaturated media. As the equa- tion contains two unknown functions, the pressure head h and the water content 0, it is necessary to make use of the material's soil-moisture retention curve either in the form

7th International Symposium on Enabling Technologies for Life Sciences (ETP)

7^th International Symposium on Enabling Technologies for Life Sciences (ETP)

ICP-MS-assisted identification of selenium-containing proteins in 2D gels using a new capillary HPLC–ICP MS interface and Orbitrap tandem mass spectrometry

An improved instrumental approach is discussed for the identification of Se-containing proteins separated by 2D polyacrylamide gel electrophoresis. A protein, detected in a gel by laser ablation ICP-MS 2D 78Se imaging, was excised from another gel obtained in parallel under identical conditions, and digested with trypsin. Selenium-peptides were detected by capillary HPLC–ICP MS using a new robust commercial interface and an ICP mass spectrometer fitted with a frequency-matching RF generator facilitating work at high concentrations of acetonitrile in the mobile phase. The identification of selenopeptides was carried out by means of hybrid linear quadrupole trap-Orbital trap MS offering a higher intrascan dynamic range and better mass accuracy than the hitherto used Q-TOF (time-of-flight) mass spectrometers. An example of the identification of Se-containing glyceraldehyde-3-phosphate dehydrogenase-3 in yeast is discussed.

TiO2 nanoparticles induce endothelial cell activation in a pneumocyte–endothelial co-culture model

The effects of particulate matter (PM) on endothelial cells have been evaluated in vitro by exposing isolated endothelial cells to different types of PM. Although some of the findings from these experiments have been corroborated by in vivo studies, an in vitro model that assesses the interaction among different cell types is necessary to achieve more realistic assays. We developed an in vitro model that mimics the alveolar–capillary interface, and we challenged the model using TiO2 nanoparticles (TiO2-NPs). Human umbilical endothelial cells (HUVECs) were cultured on the basolateral side of a membrane and pneumocytes (A549) on the apical side. Confluent co-cultures were exposed on the apical side to 10μg/cm2 of TiO2-NPs or 10ng/mL of TNFα for 24h. Unexposed cultures were used as negative controls. We evaluated monocyte adhesion to HUVECs, adhesion molecule expression, nitric oxide concentration and proinflammatory cytokine release. The TiO2-NPs added to the pneumocytes induced a 3- to 4-fold increase in monocyte adhesion to the HUVECs and significant increases in the expression of adhesion molecules (4-fold for P-selectin at 8h, and about 8- and 10-fold for E-selectin, ICAM-1, VCAM-1 and PECAM-1 at 24h). Nitric oxide production also increased significantly (2-fold). These results indicate that exposing pneumocytes to TiO2-NPs causes endothelial cell activation.

Molecular discriminators using single wall carbon nanotubes

The interaction between single wall carbon nanotubes (SWNTs) and amphiphilic molecules has been studied in a solid phase. SWNTs are allowed to interact with different amphiphilic probes (e.g. lipids) in a narrow capillary interface. Contact between strong hydrophobic and amphiphilic interfaces leads to a molecular restructuring of the lipids at the interface. The geometry of the diffusion front and the rate and the extent of diffusion of the interface are dependent on the structure of the lipid at the interface. Lecithin having a linear tail showed greater mobility of the interface as compared to a branched tail lipid like dipalmitoyl phosphatidylcholine, indicating the hydrophobic interaction between single wall carbon nanotube core and the hydrophobic tail of the lipid. Solid phase interactions between SWNT and lipids can thus become a very simple but efficient means of discriminating amphiphilic molecules in general and lipids in particular.

Quantitative multiple reaction monitoring of peptide abundance introduced via a capillary zone electrophoresis-electrospray interface.

We demonstrate the use of capillary zone electrophoresis with an electrokinetic sheath-flow electrospray interface coupled to a triple-quadrupole mass spectrometer for the accurate and precise quantification of Leu-enkephalin in a complex mixture using multiple-reaction monitoring (MRM). Assay time is <6 min, with no re-equilibration required between runs. A standard curve of Leu-enkephalin was performed in the presence of a background tryptic digest of bovine albumin. We demonstrate reasonably reproducible peak heights (21% relative standard deviation), retention times (better than 1% relative standard deviation), and robust electrospray quality. Our limit of detection (3σ) was 60 pM, which corresponds to the injection of 335 zmol of peptide. This is a 10-20-fold improvement in mass sensitivity than we have obtained by nano HPLC/MRM and substantially better than reported for LC/MS/MS. Further quantification was performed in the presence of stable-isotope-labeled versions of the peptides; under these conditions, linearity was observed across nearly 4 orders of magnitude. The concentration detection limit was 240 pM for the stable-isotope-labeled quantification.

Detection of a Thousand Copies of miRNA without Enrichment or Modification

We report direct quantitative analysis of multiple miRNAs with a detection limit of 1000 copies without miRNA enrichment or modification. A 300-fold improvement over the previously published detection limit was achieved by combining capillary electrophoresis with confocal time-resolved fluorescence detection through an embedded capillary interface. The method was used to determine levels of three miRNA biomarkers of breast cancer (miRNA 21, 125b, 145) in a human breast cancer cell line (MCF-7). A 30 pL volume of the cell lysate with approximately a material content of a single cell was sampled for the analysis. MiRNA 21, which is up-regulated in breast cancer, was detected at a level of approximately 12 thousand copies per cells. MiRNAs 125b and 145, which are down-regulated in breast cancer, were below the 1000-copy detection limit. This sensitive method may facilitate the analysis of miRNA in fine-needle-biopsy samples and even in single cells without enrichment or modification of miRNA. Advantageously, the instrumental setup developed here can be reproduced by others as it requires no sophisticated custom-made parts.

Endurance but not resistance training increases intra‐myocellular lipid content and β‐hydroxyacyl coenzyme A dehydrogenase activity in active elderly men

Endurance and resistance training (ET and RT, respectively) in older subjects have been proven beneficial against metabolic or cardiovascular disorders and against sarcopaenia respectively. Like ET, RT may also increase muscle oxidative capacities. In addition, it could be questioned whether RT, similarly to ET, is able to increase muscle energetic stores such as intra-myocellular lipids (IMCL) and glycogen contents. To evaluate a possible ET- and RT-induced parallel increase in oxidative capacity and energetic stores, active elderly men (72 ± 2 years) were submitted to a 14-week training programme (three times week(-1) ) combining lower body endurance and upper body resistance. Muscle samples were collected in ET vastus lateralis (VLat) and RT deltoid (Del) muscles before and after training. IMCL and glycogen contents were assessed by histochemistry (Oil Red O and periodic acid-Schiff staining, respectively) and by biochemical assay for glycogen. Citrate synthase (CS, marker of mitochondrial citric acid cycle), β-hydroxyacyl coenzyme A dehydrogenase (β-HAD, beta-oxidation) and phosphofructokinase (PFK, glycolytic pathway) activities were determined and so was the capillary interface index (LC/PF). Both training regimens significantly increased CS and LC/PF in ET-VLat and RT-Del. IMCL content and β-HAD activity increased (P < 0.05) only in ET-VLat, whereas PFK activity increased (P < 0.05) only in RT-Del. Glycogen content was not significantly altered in response to training in both muscles. Unlike RT, which induced an increase in PFK, ET is able to increase IMCL content and β-oxidation capacity in active elderly men, even though both training may improve CS activity and LC/PF.

Automated Digital Microfluidic Sample Preparation for Next-Generation DNA Sequencing

Next-generation sequencing (NGS) technology is a promising tool for identifying and characterizing unknown pathogens, but its usefulness in time-critical biodefense and public health applications is currently limited by the lack of fast, efficient, and reliable automated DNA sample preparation methods. To address this limitation, we are developing a digital microfluidic (DMF) platform to function as a fluid distribution hub, enabling the integration of multiple subsystem modules into an automated NGS library sample preparation system. A novel capillary interface enables highly repeatable transfer of liquid between the DMF device and the external fluidic modules, allowing both continuous-flow and droplet-based sample manipulations to be performed in one integrated system. Here, we highlight the utility of the DMF hub platform and capillary interface for automating two key operations in the NGS sample preparation workflow. Using an in-line contactless conductivity detector in conjunction with the capillary interface, we demonstrate closed-loop automated fraction collection of target analytes from a continuous-flow sample stream into droplets on the DMF device. Buffer exchange and sample cleanup, the most repeated steps in NGS library preparation, are also demonstrated on the DMF platform using a magnetic bead assay and achieving an average DNA recovery efficiency of 80%±4.8%.

Mass Transport in a Micro Flow-Through Vial of a Junction-at-the-Tip Capillary Electrophoresis-Mass Spectrometry Interface

When coupling capillary electrophoresis with postcolumn detection methods, such as mass spectrometry, the presence of postcolumn band broadening must be considered. The band broadening effects introduced by junction-at-the-tip CE-MS interfaces using a postcolumn micro flow-through vial are investigated by studying the hydrodynamic flow patterns and mass transport process inside the micro vial at the end of the CE separation capillary. Simulation results obtained by solving the Navier-Stokes and mass balance equations provide insights into the velocity field and concentration distribution of the analytes in the micro vial and demonstrate that, with a low flow rate of chemical modifier solution, the laminar flow streams confine the analyte molecules to the central part of the micro vial and thus maintain major features of the peak shapes. Peaks detected by UV and MS under similar experimental conditions were compared to verify the numerical prediction that the main features of the UV peak can be retained in the MS peak. Experiments also show that band broadening can be minimized when an appropriate chemical modifier flow rate is selected.

Characterization of a condensed‐phase membrane introduction mass spectrometry (CP‐MIMS) interface using a methanol acceptor phase coupled with electrospray ionization for the continuous on‐line quantitation of polar, low‐volatility analytes at trace levels in complex aqueous samples

We report the development and application of a capillary hollow fibre membrane interface using methanol as an acceptor phase to deliver target analytes to an electrospray ionization source and a triple quadrupole mass spectrometer. Superior fluid handling systems lead to greater signal stability and membrane integrity for the continuous on-line monitoring of polar and charged analytes in complex aqueous samples with detection limits in the parts-per-trillion to parts-per-billion range. The system can be operated in either a continuous flow or a stopped acceptor flow mode - the latter giving rise to greater sensitivity. We report detection limits, enrichment factors and signal response times for selected analytes with polydimethylsiloxane and Nafion® polymer membrane interfaces. In addition, we demonstrate the use of this interface to detect pharmaceuticals and other contaminants in natural water and artificial urine. The improved sensitivity and analytical response times of our CP-MIMS system make it possible to continuously monitor dynamic chemical systems with temporal resolutions on the order of minutes. Presented is a comparison of the performance of CP-MIMS versus direct infusion electrospray ionization, demonstrating the potential advantages over direct infusion for trace analyte measurements in complex, high ionic strength samples. Furthermore, by continuously flowing a reaction mixture in a closed loop over the interface, we demonstrate the use of the system as an in situ reaction-monitoring platform for the chlorination of a model organic compound in aqueous solution.

A liquid chromatography to capillary array electrophoresis interface for two-dimensional separations

A new liquid chromatography-capillary electrophoresis interface has been developed for multidimensional separations. The interface allows two second dimension separation capillaries to sample the chromatography effluent by servo controlled positioning of the capillary inlets in either the effluent or background electrolyte streams. The use of multiple second dimension capillaries allows higher first dimension sampling rates or multiple second dimension separation modes. Fluorescently labelled serum was separated by gel filtration and sub-micellar capillary array electrophoresis producing a multidimensional separation. Alternatively, using different background electrolytes for each capillary, two multidimensional separations with different selectivities were collected simultaneously. An easily fabricated PDMS multichannel sheath-flow cuvette was used for sensitive laser induced fluorescence detection of the labelled serum.

Biases in Ion Transmission Through an Electrospray Ionization-Mass Spectrometry Capillary Inlet

A heated capillary inlet for an electrospray ionization mass spectrometry (ESI-MS) interface was compared with shorter versions of the inlet to determine the effects on transmission and ionization efficiencies for low-flow (nano) electrosprays. Five different inlet lengths were studied, ranging from 6.4 to 1.3 cm. As expected, the electrospray current transmission efficiency increased with decreasing capillary length due to reduced losses to the inside walls of the capillary. This increase in transmission efficiency with shorter inlets was coupled with reduced desolvation of electrosprayed droplets. Surprisingly, as the inlet length was decreased, some analytes showed little or no increase in sensitivity, while others showed as much as a 15-fold gain. The variation was shown to be at least partially correlated with analyte mobilities, with the largest gains observed for higher mobility species, but also affected by solution conductivity, flow rate, and inlet temperature. Strategies for maximizing sensitivity while minimizing biases in ion transmission through the heated capillary interface are proposed.

Numerical modeling of two-phase hysteresis combined with an interface condition for heterogeneous porous media

This paper presents a numerical implementation of two-phase capillary hysteresis and its combination with a capillary interface condition for the treatment of heterogeneities. The hysteresis concepts chosen in this work are first implemented in a node-centered FV discretization scheme and subsequently combined with the interface condition that predicts sharp saturation discontinuities at material interfaces, based on a pressure equilibrium concept. This approach allows for the approximation of history-dependent, and at the same time discontinuous, saturations at material interfaces. The resulting model provides a well-defined evolution of the hysteretic capillary pressure–saturation relationships at material interfaces that is independent of the grid spacing. As demonstrated with a simple 1-D example, this concept therefore offers the advantage that the solution of a two-phase flow problem involving hysteresis does not relate to the grid resolution at the material interfaces.

Freezing, fragmentation, and charge separation in sonic sprayed water droplets

Water droplets are generated by sonic spray, transferred into vacuum through a capillary interface, and then passed through two image charge detectors separated by a drift region. The image charge detectors measure the charge and velocity of each droplet. For around 1% of the droplets, the charge changes significantly between the detectors. In some cases it increases, in others it decreases, and for some droplets the charge changes polarity. We attribute the charge changing behavior to fragmentation caused by freezing. Simulations indicate that the time required for a droplet to cool and freeze in vacuum depends on its size, and that droplets with radii of 1–2 μm have the right size to freeze between the two detectors. These sizes correspond to the smaller end of the distribution present in the experiment. When the charge on a droplet increases or changes polarity, fragmentation must be accompanied by charge separation where fragments carry away opposite charges. In some cases, two fission fragments were observed in the second charge detector. We show examples where the droplet breaks apart to give fragments of the same charge and opposite charges. The fragmentation and charge changing behavior found here is consistent with what has been found in the freezing of larger suspended and supported droplets.