Multivalent binding of small guest molecules and proteins to molecular printboards inside microchannels

Beta-Cyclodextrin (beta-CD) monolayers have been immobilized in microchannels. The host-guest interactions on the beta-CD monolayers inside the channels were comparable to the interactions on beta-CD monolayers on planar surfaces, and a divalent fluorescent guest attached with a comparable binding strength. Proteins were attached to these monolayers inside microchannels in a selective manner by employing a strategy that uses streptavidin and orthogonal linker molecules. The design of the chip, which involved a large channel that splits into four smaller channels, allowed the channels to be addressed separately and led to the selective immobilization of antibodies. Experiments with labeled antibodies showed the selective immobilization of these antibodies in the separate channels.     

Stripline probes for nuclear magnetic resonance

A novel route towards chip integrated NMR analysis is evaluated. The basic element in the design is a stripline RF 'coil' which can be defined in a single layer lithographic process and which is fully scalable to smaller dimensions. The sensitivity of such a planar structure can be superior to that of a conventional 3D helix. The basic properties, such as RF field strength, homogeneity and susceptibility broadening are discussed in detail. Secondary effects related to the thermal characteristics are discussed in simplified models. Preliminary NMR tests of basic solid and liquid samples measured at 600 MHz confirm the central findings of the design study. It is concluded that the stripline structure can be a valuable addition to the NMR toolbox; it combines high sensitivity with low susceptibility broadening and high power handling capabilities in a simple scalable design.     

A two-sided Arnoldi algorithm with stopping criterion and MIMO selection procedure

In this paper we introduce a two-sided Arnoldi method for the reduction of high order linear systems and we propose useful extensions, first of all a stopping criterion to find a suitable order for the reduced model and secondly, a selection procedure to significantly improve the performance in the multi-input multi-output (MIMO) case. One application is in micro-electro-mechanical systems (MEMS). We consider a thermo-electric micro thruster model, and a comparison between the commonly used Arnoldi algorithm and the two-sided Arnoldi is performed.     

Quantification of electrical field-induced flow reversal in a microchannel

We characterize the electroosmotic flow in a microchannel with field effect flow control. High resolution measurements of the flow velocity, performed by micro particle image velocimetry, evidence the flow reversal induced by a local modification of the surface charge due to the presence of the gate. The shape of the microchannel cross-section is accurately extracted from these measurements. Experimental velocity profiles show a quantitative agreement with numerical results accounting for this exact shape. Analytical predictions assuming a rectangular cross-section are found to give a reasonable estimate of the velocity far enough from the walls.     

Electrokinetic sorting and collection of fractions for preparative capillary electrophoresis on a chip

A microfabricated device capable of selecting and collecting multiple components from a mixture separated by capillary electrophoresis (CE) is described. This collection is automated and can be easily controlled by a set of rules defined by an operator, enabling fast and consistent operation. The device consists of an electrokinetically steered fluidic network that can be divided into three sections: a CE part, a fractions distribution region and a set of storage channels. Sample fractions leave the CE channel and are detected in the interfacial region by fluorescence intensity measurements. If an upcoming peak is detected, separation is withheld and the potentials are reconfigured to force the fraction into one of the collection channels, where they become available for further processing or analysis. The sequence of separation and collection is repeated until all the bands of interest are captured. A mixture of three fluorescent dyes (Rhodamine 6G, Rhodamine B and Fluorescein) was used to demonstrate the principle. The components were repeatedly separated by means of CE and pooled in their respective storage channels. In comparison to previous developments, the system presented in this paper offers automatic collection of all fractions in a single run. Furthermore, it is possible to run the system in a repetitive mode for accumulative pooling if more fractionated sample is required.     

Use of 120-nm deep channels for liquid chromatographic separations

The present study reports on the exploration of the separation speed limits of RPLC chromatography in open-tubular channels. Applying the shear-driven chromatography principle in a 120-nm deep open channel, and using an improved detection set-up, the separation of three coumarin dyes was detectable 8mm downstream of the injection point. At this distance, separation efficiencies of N = 17,900 - 24,100 plates were obtained at a velocity of 10 mm s(-1), corresponding to a plate generation velocity of 21,100 to 28,300 plates per second for the most and least retained component, respectively.     

Effect of the presence of an ordered micro-pillar array on the formation of silica monoliths

We report on the synthesis of siloxane-based monoliths in the presence of a two-dimensional, perfectly ordered array of micro-pillars. Both methyltrimethoxysilane- and tetramethoxysilane-based monoliths were considered. The obtained structures were analyzed using scanning-electron microscopy and can be explained from the general theory of surface-directed phase separation in confined spaces. The formed structures are to a large extent nearly exclusively determined by the ratio between the bulk domain size of the monolith on the one hand and the distance between the micro-pillars on the other hand. When this ratio is small, the presence of the pillars has nearly no effect on the morphology of the produced monoliths. However, when the ratio approaches unity and ascends above it, some new types of monolith morphologies are induced, two of which appear to have interesting properties for use as novel chromatographic supports. One of these structures (obtained when the domain size/inter-pillar distance ratio is around unity) is a 3D network of linear interconnections between the pillars, organized such that all skeleton branches are oriented perpendicular to the micro-pillar surface. A second interesting structure is obtained at even higher values of the domain size/inter-pillar distance ratio. In this case, each individual micro-pillar is uniformly coated with a mesoporous shell.     

Sonoluminescence and sonochemiluminescence from a microreactor

Micromachined pits on a substrate can be used to nucleate and stabilize microbubbles in a liquid exposed to an ultrasonic field. Under suitable conditions, the collapse of these bubbles can result in light emission (sonoluminescence, SL). Hydroxyl radicals (OH()) generated during bubble collapse can react with luminol to produce light (sonochemiluminescence, SCL). SL and SCL intensities were recorded for several regimes related to the pressure amplitude (low and high acoustic power levels) at a given ultrasonic frequency (200kHz) for pure water, and aqueous luminol and propanol solutions. Various arrangements of pits were studied, with the number of pits ranging from no pits (comparable to a classic ultrasound reactor), to three-pits. Where there was more than one pit present, in the high pressure regime the ejected microbubbles combined into linear (two-pits) or triangular (three-pits) bubble clouds (streamers). In all situations where a pit was present on the substrate, the SL was intensified and increased with the number of pits at both low and high power levels. For imaging SL emitting regions, Argon (Ar) saturated water was used under similar conditions. SL emission from aqueous propanol solution (50mM) provided evidence of transient bubble cavitation. Solutions containing 0.1mM luminol were also used to demonstrate the radical production by attaining the SCL emission regions.     

An automated injection system for sub-micron sized channels used in shear-driven-chromatography

This paper describes a method to automatically and reproducibly inject sharply delimited sample plugs in the shallow (i.e., sub-micron) channels typically used in shear driven chromatography. The formation of asymmetric plugs, which typically occurs during loading of the sample in wide channels, is circumvented by etching a slit in the middle of the channel that is connected to a micro-well and a vacuum system with syringes for the supply of both the analyte and the mobile phase. The design of the injection slit was supported by a series of CFD simulations to optimize its shape and that of the corresponding injection well. The system was intensively tested experimentally and showed good reproducibility, both for the width and the area of the injected peaks (relative standard deviations are max. 4 and 6%, respectively). The concentration of the injected plug was found to be approximately 80% of the original sample concentration. It was also observed that with the current setup the lower limit of the peak width was about 120 microm. This is a consequence of the fact that the peak width originating from the convection filling step becomes negligible to the contribution of diffusion during the filling and flushing time. Being fully automated and perfectly closed, the presently proposed injection system also paves the way to integrate other functionalities in shear driven chromatography, i.e. gradient elution and parallelization.