Valves and flow injection manifolds: an excellent marriage with unlimited versatility

An overview of the functions of valves—both injection and selection valves—in flow injection (FI) for manipulating the manifold as a function of both necessities and imagination of the user is reported. The use of single valves for sample or reagent injection, for housing different devices (namely, minicolumns and other separation units, flow-cells, etc.) is discussed. Multiple injection valve arrangements (in-series, in-parallel and inner coupling) that give place to FI modes as merging-zones (both symmetrical and asymmetrical), trapping-zone and nested-loop approaches are exposed. The possible locations of selection valves in the FI manifold are presented and the problems each design can solve are commented.     

Evaluation of different nonspecific binding blocking agents deposited inside poly(methyl methacrylate) microfluidic flow-cells

Poly(methyl methacrylate) (PMMA) flow-cells containing microwells were deposited with different nonspecific binding blocking agents, namely, bovine serum albumin (BSA), cationic lipid (DOTAP:DOPE) and diethylene glycol dimethyl ether (DEGDME). Water contact angle (WCA) and atomic force microscope (AFM) measurements were carried out to confirm the successful depositions of BSA, DOTAP, and DEGDME onto the PMMA surfaces. Fluorescent intensity measurements were performed to evaluate the degree of nonspecific adsorption of Cy5-labeled anti-IgG proteins onto plain and oxygen plasma-treated (PT) PMMA flow-cells as well as PMMA flow-cells deposited with different above-mentioned blocking agents. We then employed a label-free detection method called total internal reflection ellipsometry (TIRE) to evaluate the stability of the deposited blocking agents inside the PMMA flow-cells. It was found that, while DOTAP:DOPE was the best agent for blocking the nonspecific adsorption, it could be removed from the PMMA surfaces of the flow-cells upon rinsing with phosphate buffered saline (PBS) and later deposited back onto the Au-coated glass sensing substrate of the TIRE. The removal of the blocking agents from PMMA surfaces and their deposition onto the sensing substrate were further manifested by measuring the kinetics and the amount of adsorbed anti-α-hCG proteins. Overall, the dry DEGDME coating by plasma-enhanced chemical vapor deposition (PECVD) showed very good blocking and excellent stability for subsequent assay inside the microwells. Our results could be useful when one considers what blocking agents should be used for PMMA-based microfluidic immunosensor or biosensor devices by looking at both the blocking efficiency and the stability of the blocking agent.     

Les proprietes hydrodynamiques des polystyrenes atactiques en solvant theta

Light scattering, sedimentation velocity and intrinsic viscosity measurements were made, at 35° in cyclohexane, for various well fractionated atactic polystyrenes. It was found that these solution properties can vary from a sample to another, revealing structural differences among the samples. The variations in the sedimentation velocity law can entirely be ascribed to the corresponding variations in the chain dimensions. In this respect, the results are in accordance with the Kirkwood-Riseman's theory. On the contrary, this theory in its present state cannot explain the variations in the intrinsic viscosity law in relation with the chain dimensions variations. These results put back in question the possibility, even in a theta solvent, of using intrinsic viscosity measurements, as suggested by Flory, for calculation of chain dimensions.     

Analytical solutions for velocity, temperature and concentration distribution in electroosmotic microchannel flows of a non-Newtonian bio-fluid

In this paper, analytical solutions are derived, describing the transport characteristics of a non-Newtonian fluid flow in a rectangular microchannel, under the sole influence of electrokinetic forces. Apart from estimating the fully-developed velocity and temperature distributions, an explicit expression is derived for solutal concentration distribution within the microchannel. Finally, as an illustrative case study, the flow behaviour of a blood sample is analyzed, in which the flow parameters are modeled as functions of the hematocrit fraction in the sample. It is revealed that a higher hematocrit fraction may result in significant reductions in species concentration levels, on account of stronger dispersions in the velocity profiles, characterized by more significant viscous effects. It is also demonstrated that cases in which characteristic length scale of RBC suspensions turns out to be consequential relative to the microchannel dimensions, a significant augmentation in the electroosmotic transport may occur. Such observations can be of particular significance in the design of electroosmotically actuated bio-microfluidic systems as efficient solutal carriers.     

Micro-impedance cytometry for detection and analysis of micron-sized particles and bacteria

The sensitivity of a microfluidic impedance flow cytometer is governed by the dimensions of the sample analysis volume. A small volume gives a high sensitivity, but this can lead to practical problems including fabrication and clogging of the device. We describe a microfluidic impedance cytometer which uses an insulating fluid to hydrodynamically focus a sample stream of particles suspended in electrolyte, through a large sensing volume. The detection region consists of two pairs of electrodes fabricated within a channel 200 μm wide and 30 μm high. The focussing technique increases the sensitivity of the system without reducing the dimensions of the microfluidic channel. We demonstrate detection and discrimination of 1 μm and 2 μm diameter polystyrene beads and also Escherichia coli. Impedance data from single particles are correlated with fluorescence emission measured simultaneously. Data are also compared with conventional flow cytometry and dynamic light scattering: the coefficient of variation (CV) of size is found to be comparable between the systems.     

Capillary SFC-FTIR – effects of the flow-cell on chromatographic resolution

The quantitative effects on chromatographic resolution of FTIR flow-cells for detection in capillary SFC have been determined. A suitably designed cell with a volume of 500 nl was shown to cause only modest broadening of chromatographic peaks obtained from the surfactant mixture Triton X-100, showing that subsequent detection methods can therefore be used in a multi-hyphenated chromatographic ensemble. A larger-volume (980 nl) cell was found to give satisfactory results with 100 μ columns, but not with 50 μm columns. The practicability of a multi-hyphenated system was illustrated by a preliminary capillary SFC-UV-FTIR-FID study on a plant extract. Good infrared spectra were obtained, together with well-resolved UV and (subsequent) FID chromatograms.     

Characterization of microconcentric nebulizer uptake rates for capillary electrophoresis inductively coupled plasma mass spectrometry

There is demonstrated interest in combining capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) for speciation determinations. When self-aspirating nebulizers are used for this application, it is important to offset the suction effect to avoid degradation of the separation. In this study, sample uptake rates for three microconcentric nebulizers of the same model, in combination with a cyclonic spray chamber, were characterized and compared for future utilization in CE–ICP-MS interfaces. The specific model studied was a MicroMist with a nominal uptake rate of 100 μl/min at 1 l/min argon gas flow rate per the manufacturer's specifications. Sample uptake rates at various nebulizer gas flows were measured by aspirating water from a weighed container and calculating the uptake rate in microliter per minute. The nebulizers studied provided good reproducibility from day to day, but a comparison of the different nebulizers reflected a significant difference in performance. A characteristic observed during the study was that uptake rates decreased with increasing nebulizer gas flow. This can be used for sample introduction for CE–ICP-MS. Interestingly, very different performance was observed when comparing the three different nebulizers of the same model. Uptake rates showed strong dependence on argon gas flow rates and the dimensions of the sample uptake tubing.     

A novel deep reactive ion etched (DRIE) glass micro-model for two-phase flow experiments

In the last few decades, micro-models have become popular experimental tools for two-phase flow studies. In this work, the design and fabrication of an innovative, elongated, glass-etched micro-model with dimensions of 5 × 35 mm(2) and constant depth of 43 microns is described. This is the first time that a micro-model with such depth and dimensions has been etched in glass by using a dry etching technique. The micro-model was visualized by a novel setup that allowed us to monitor and record the distribution of fluids throughout the length of the micro-model continuously. Quasi-static drainage experiments were conducted in order to obtain equilibrium data points that relate capillary pressure to phase saturation. By measuring the flow rate of water through the flow network for known pressure gradients, the intrinsic permeability of the micro-model's flow network was also calculated. The experimental results were used to calibrate a pore-network model and test its validity. Finally, we show that glass-etched micro-models can be valuable tools in single and/or multi-phase flow studies and their applications.     

On-Line Coupling of Separation Techniques to NMR

The hyphenation of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and molecular compositions of mixtures. Most of the routinely used NMR flow-cells have detection volumes between 40–180 μL for conventional separations with analytical columns, and the newest designs employ detection volumes in the order of 200 nL for capillary separations. The low flow rates used in capillary chromatography permit the use of deuterated solvents. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow capillary HPLC-NMR experiments.     

间歇电喷雾的初步研究

设计了一种高灵敏的质谱离子化方法-间歇电喷雾，并介绍了间歇电喷雾的基本原理、稳定性和应用在蛋白质分析上的优势。这种质谱离子化方法能够显著地改善信噪比，降低对样品溶解度的要求，提高样品的离子化效率，减少样品的消耗和仪器的污染，可以预言间歇电喷雾的方法在蛋白质的分析上将会有广泛的应用前景。     

On necessary precautions when measuring solid polymer linear viscoelasticity with dynamic analysis in torsion

Solid polymer linear viscoelasticity in shear is often characterized by applying torsion and using the Saint-Venant solution when rectangular prismatic specimens are considered. It is shown that experimental dynamic torsion tests can show a dependency of the storage modulus and damping factor on the dimensions of the rectangular prismatic specimen when linear temperature ramps are applied. While the discrepancy of damping factor is explained by temperature heterogeneities and can be corrected easily by applying temperature steps, the inconsistency of storage modulus is due to an invalid application of the Saint-Venant solution. Finite element simulations allowed definition of the sample dimensions for which the Saint-Venant solution provides a good approximation, and a coefficient is given to correct the results obtained with commercial instruments when other sample dimensions are used.     

Spatial and Temporal Control Over Multilayer Bio‐Polymer Film Assembly and Composition

Biosensing applications have taken advantage of lab‐on‐a‐chip technologies for sample handling and sensors integration for highly sensitive, specific detection with high throughput. These systems are based on 2.5D fabrication principles with sensing elements restricted to an array format in two dimensions. In this report, a sensing platform that recovers biosensing capabilites in three spatial dimensions is presented. This is achieved by leveraging chitosan, a stimulus responsive polyaminosaccharide that undergoes a sol–gel transition driven by a change of pH. This process can be repeated, resulting in a multilayered hydrogel stack where each layer carries a unique chemical identity. In addition, the functionality of chitosan can be modified prior to or during the assembly process. This is demonstrated by introducing both a carboxylic acid functionality and additional primary amines to the base chitosan polymer. The assembly process is shown to be compatible with microfluidic dimensions.     

Zur multivariaten Auswertung von Ringversuchen

Summary The advantages and drawbacks of some graphical methods as interpreting aids for cooperative tests are demonstrated using results of slag sample analyses (5 laboratories, 7 components). In cases of low dimensions (components) the method of regular polygons has been found most informative. For higher dimensions modern data analysis techniques, such as principal components analysis (pca), correspondence analysis and discriminant analysis are to be preferred. From pca of correlation matrices one can also derive best choices of feature subsets to construct good polygons. The sensitivity of partial correlation coefficients due to deviating laboratory manners can be assessed by leaving-one-out comparisons.     

Unit-cell dimensions of bulk- and solution-crystallized linear polyethylene

The unit-cell dimensions and density, at room temperature, of bulk- and solution-crystallized linear polyethylene have been determined. The macroscopic measured densities for the bulk-crystallized samples ranged from 0.917 to 0.993 g/cc, and the lattice parameters were found to be independent of the sample density. In contrast, for solution-formed crystals, despite the limited range in macroscopic densities that can be attained, there is a systematic variation in the a and b dimensions with the measured density and the crystallite thickness. The implication of these results for the calculation of the degree of crystallinity and the interpretation of certain infrared bands are discussed.     

Single channel layer, single sheath-flow inlet microfluidic flow cytometer with three-dimensional hydrodynamic focusing

Flow cytometry is a technique capable of optically characterizing biological particles in a high-throughput manner. In flow cytometry, three dimensional (3D) hydrodynamic focusing is critical for accurate and consistent measurements. Due to the advantages of microfluidic techniques, a number of microfluidic flow cytometers with 3D hydrodynamic focusing have been developed in recent decades. However, the existing devices consist of multiple layers of microfluidic channels and tedious fluidic interconnections. As a result, these devices often require complicated fabrication and professional operation. Consequently, the development of a robust and reliable microfluidic flow cytometer for practical biological applications is desired. This paper develops a microfluidic device with a single channel layer and single sheath-flow inlet capable of achieving 3D hydrodynamic focusing for flow cytometry. The sheath-flow stream is introduced perpendicular to the microfluidic channel to encircle the sample flow. In this paper, the flow fields are simulated using a computational fluidic dynamic (CFD) software, and the results show that the 3D hydrodynamic focusing can be successfully formed in the designed microfluidic device under proper flow conditions. The developed device is further characterized experimentally. First, confocal microscopy is exploited to investigate the flow fields. The resultant Z-stack confocal images show the cross-sectional view of 3D hydrodynamic with flow conditions that agree with the simulated ones. Furthermore, the flow cytometric detections of fluorescence beads are performed using the developed device with various flow rate combinations. The measurement results demonstrate that the device can achieve great detection performances, which are comparable to the conventional flow cytometer. In addition, the enumeration of fluorescence-labelled cells is also performed to show its practicality for biological applications. Consequently, the microfluidic flow cytometer developed in this paper provides a practical platform that can be used for routine analysis in biological laboratories. Additionally, the 3D hydrodynamic focusing channel design can also be applied to various applications that can advance the lab on a chip research.     

Modeling of flow in a polymeric chromatographic monolith

The flow behavior of a commercial polymeric monolith was investigated by direct numerical simulations employing the lattice-Boltzmann (LB) methodology. An explicit structural representation of the monolith was obtained by serial sectioning of a portion of the monolith and imaging by scanning electron microscopy. After image processing, the three-dimensional structure of a sample block with dimensions of 17.8 μm × 17.8 μm × 14.1 μm was obtained, with uniform 18.5 nm voxel size. Flow was simulated on this reconstructed block using the LB method to obtain the velocity distribution, and in turn macroscopic flow properties such as the permeability and the average velocity. The computed axial velocity distribution exhibits a sharp peak with an exponentially decaying tail. Analysis of the local components of the flow field suggests that flow is not evenly distributed throughout the sample geometry, as is also seen in geometries that exhibit preferential flow paths, such as sphere pack arrays with defects. A significant fraction of negative axial velocities are observed; the largest of these are due to flow along horizontal pores that are also slightly oriented in the negative axial direction. Possible implications for mass transfer are discussed.     

Remotely detected MRI velocimetry in microporous bead packs

Many NMR and MRI methods probe fluid dynamics within macro- and mesoporous materials, but with few exceptions, they report on its macroscopically averaged properties. MRI methods are generally unable to localize microscopic features of flow within macroscopic samples because the fraction of the enclosing detector volume occupied by these features is so small. We have recently overcome this problem using remotely detected MRI velocimetry, a technique in which spatial, chemical, and velocity information about elements of the flow is encoded with a conventional NMR coil and detected sensitively at the sample outflow by a volume-matched microdetector. Here, we apply this method to microporous model systems, recording MRI images that correlate local velocity, spin relaxation, and time-of-flight in microscopic resolution and three spatial dimensions. Our results illustrate that remotely detected MRI is an effective approach to elucidate flow dynamics in porous materials including bead pack microreactors and chromatography columns.     

Measurement of enzyme kinetics using microscale steady-state kinetic analysis

This paper describes a new technique--microscale steady-state kinetic analysis (microSKA)--that enables the rapid and parallel analysis of enzyme kinetics. Rather than physically defining a microscopic reactor through microfabrication, we show how the relative rates of reaction and transport in a macroscopic flow chamber, where the enzyme is immobilized on one wall of the chamber, results in the confinement of an enzyme-catalyzed reaction to a microscopic reactor volume adjacent to this wall. This volume has linear dimensions that are orders of magnitude smaller than the physical dimensions of the system (i.e., micrometer vs millimeter). Conversion within this volume is monitored at steady state as a function of position, rather than time. In this way, limitations due to reactor dead time and mixing are avoided. We use microSKA to determine kinetic parameters for the alkaline phosphatase-catalyzed de-phosphorylation of nonfluorescent methylumbelliferyl phosphate (MUP) to fluorescent 7-hydroxy-4-methylcoumarin (HMC) at two different values of pH. Kinetic parameters measured with microSKA are in good agreement with values obtained using conventional methods, if one takes into account effects of immobilization on enzyme activity. This technique provides a rapid and simple method for determining enzyme kinetics using small amounts of sample material and may be useful for applications in proteomics, drug discovery, biocatalyst development, and clinical diagnostics.     

Numerical modelling of sample–furnace thermal lag in dynamic mechanical analyser

Due to dynamic nature of processes taking place during the experiment (chemical reaction and physical processes, heat flow, gas flow, etc.) the results obtained by thermal methods may considerably depend on the conditions used during the experiment. Therefore, whenever the results of thermal analysis are reported, the experimental conditions used should be stated. In this paper we have studied the heat transfer from the furnace to the sample and through the sample during dynamic mechanical analysis measurements. Numerical modelling of the heat transfer was done using an own computer program based on the heat conduction equation, solved numerically applying the finite difference methods. The calculated values of the thermal lag between the furnace and the sample were compared with the values experimentally determined on samples of a composite polymeric energetic material (double-base rocket propellant). Also, the temperature distribution within the sample as a function of the heating rate was analysed using the same numerical model. It was found out that using this model and temperature dependent heat transfer coefficient, experimentally obtained values of the thermal lag between the furnace and the sample can be satisfactory described. It was also shown that even at slow heating rates, such is, e.g. 2 °C min⁻¹, the thermal lag between the furnace and the sample can reach several degrees, while the thermal gradient within 3-mm thick rectangular sample can reach 0.4 °C.     

Facilitating method development for reverse fill/flush flow modulation by using a tuneable auxiliary pressure source instead of a fixed bleed capillary

The conventional reverse fill/flush flow modulation for comprehensive two-dimensional gas chromatography requires a bleed capillary column to be connected to the outlet of the modulator channel. The purpose of this capillary, which does not contain the stationary phase, is to provide pressure resistance to the modulator channel flow. In this way, the desired modulator volumetric flow can be achieved, and channel over-filling can be avoided. Normally, the length and the internal diameter of the bleed capillary are chosen so as to obtain the modulator flow that is close to the flow of the first separation column. Thus, for any chosen set of chromatographic conditions, the required dimensions of the bleed capillary can be completely different, making the two-dimensional gas chromatography method development tedious and generating additional costs in consumables and analyst time. In this work, a tuneable pressure source generating a suitable backpressure was used instead of the fixed bleed capillary which has the advantage of the possibility to freely adapt the pressure resistance and generate the required modulator channel flow for any conditions. This set-up has been evaluated and compared in terms of the impact on the modulation performance to the set-up involving a fixed bleed capillary demonstrating comparable performance.