Glass Microchannel Research Articles

A microscopic perspective of a microreactor

The use of microreactors in (bio)chemical processes has been gaining relevance in the last decade. The low consumption of reagents, the possibility of continuous operation and the faster translation from lab- to production scale are some of the several advantages of these devices. The whole results in cost reductions in process development. Enzyme catalyzed reactions have proved to be an excellent alternative to the use of chemicals due to its ability to catalyze the most complex chemical processes under benign experimental and environmental conditions. In this way, enzymes may be crucial to the implementation of a much more sustainable chemical industry.The present work is within such scope, using as model system the immobilization of invertase in glass (silica) microchannels, for the production of fructose syrups through sucrose hydrolysis. The immobilization of the enzyme was achieved through treatment of the substrate with a sequence of coatings (Figure 1). Activation of the inner surface of the microchannels with 3-aminopropyltriethoxysilane (APTES) was followed by the introduction of a spacer, glutaraldehyde. Lastly the enzyme solution was introduced in the presence of sodium cyanoborohydride, in order to enhance the stability of the support-enzyme binding.The characterization of the coatings at each stage of the immobilization protocol was carried out to confirm the change of the microchannel surface. Such studies were performed using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analysis (Figure 1).The results obtained, namely the shifts on the surface roughness corroborate that the several coatings were successfully applied and the enzyme immobilized. Moreover, the immobilization approach used proved to be highly effective, resulting on successful continuous use of the microreactor for a period of 30 days with roughly constant full conversion of a sucrose solution of 50g/l, at a flow rate of 7µl/minute (Figure 2).Future work will involve a more extensive characterization of the several coatings by Quartz Crystal Microbalance which will be decisive to achieve a better comprehension of the coating phenomena and hence optimize the immobilization process.The authors would like to thank Fundação para a Ciência e a Tecnologia, Portugal, for financial support through contracts under the program Ciência 2007 awarded to P. Fernandes, for the doctoral grant SFRH/BD/74818/2010 awarded to F. Carvalho and for the doctoral grant SFRH/BD/71990 /2010 awarded to Patrizia Paradiso.

A Microfluidic SPLITT Device for Fractionating Low-Molecular Weight Samples

In this article, we report the design of a microfluidic split flow thin cell (SPLITT) fractionation device with internal electrodes placed across the width of its analysis channel for assaying low-molecular weight samples. The reported device allows the realization of lateral electric fields and separation distances of the orders of 100 V/cm and 500 μm, respectively, that are suitable for fractionating such mixtures with high resolution. Our experiments show that a key challenge to realizing electrophoretic fractionations using the current design is to minimize the electroosmotically driven fluid circulations in its SPLITT channel that tend to hydrodynamically mix the liquid streams flowing through this duct. The present work addresses this challenge by chemically modifying the surface of our fluidic conduits with a new coating medium, N-(2-triethoxysilylpropyl) formamide, which has been shown to diminish electroosmotic flow in glass microchannels by over 5 orders of magnitude. Finally, we describe the integration of the reported microfluidic fractionation device to a mass spectrometer via the electrospray ionization interface to allow inline label-free detection of analytes in our assay. Product purity greater than 95% has been accomplished using the SPLITT system presented here for a sample of peptides having the same electrical polarity.

Invited Article: A test-facility for large-area microchannel plate detector assemblies using a pulsed sub-picosecond laser

The Large Area Picosecond Photodetector Collaboration is developing large-area fast photodetectors with time resolution </~10 ps and space resolution </~1 mm based on atomic layer deposition-coated glass Micro-Channel Plates (MCPs). We have assembled a facility at Argonne National Laboratory for characterizing the performance of a wide variety of microchannel plate configurations and anode structures in configurations approaching complete detector systems. The facility consists of a pulsed Ti:Sapphire laser with a pulse duration ≈100 fs, an optical system allowing the laser to be scanned in two dimensions, and a computer-controlled data-acquisition system capable of reading out 60 channels of anode signals with a sampling rate of over 10 GS/s. The laser can scan on the surface of a sealed large-area photodetector, or can be introduced into a large vacuum chamber for tests on bare 8 in.-square MCP plates or into a smaller chamber for tests on 33-mm circular substrates. We present the experimental setup, detector calibration, data acquisition, analysis tools, and typical results demonstrating the performance of the test facility.

Flow patterns and pressure drop of ionic liquid–water two-phase flows in microchannels

The two-phase flow of a hydrophobic ionic liquid and water was studied in capillaries made of three different materials (two types of Teflon, FEP and Tefzel, and glass) with sizes between 200μm and 270μm. The ionic liquid was 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, with density and viscosity of 1420kgm−3 and 0.041kgm−1s−1, respectively. Flow patterns and pressure drop were measured for two inlet configurations (T- and Y-junction), for total flow rates of 0.065–214.9cm3h−1 and ionic liquid volume fractions from 0.05 to 0.8. The continuous phase in the glass capillary depended on the fluid that initially filled the channel. When water was introduced first, it became the continuous phase with the ionic liquid forming plugs or a mixture of plugs and drops within it. In the Teflon microchannels, the order that fluids were introduced did not affect the results and the ionic liquid was always the continuous phase. The main patterns observed were annular, plug, and drop flow. Pressure drop in the Teflon microchannels at a constant ionic liquid flow rate, was found to increase as the ionic liquid volume fraction decreased, and was always higher than the single phase ionic liquid value at the same flow rate as in the two-phase mixture. However, in the glass microchannel during plug flow with water as the continuous phase, pressure drop for a constant ionic liquid flow rate was always lower than the single phase ionic liquid value. A modified plug flow pressure drop model using a correlation for film thickness derived for the current fluids pair showed very good agreement with the experimental data.

Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass

The ability of 8 picosecond pulse lasers for three dimensional direct-writing in the bulk of transparent dielectrics is assessed through a comparative study with a femtosecond laser delivering 600 fs pulses. The comparison addresses two main applications: the fabrication of birefringent optical elements and two-step machining by laser exposure and post-processing by chemical etching. Formation of self-organized nano-gratings in glass by ps-pulses is demonstrated. Differential etching between ps-laser exposed regions and unexposed silica is observed. Despite attaining values of retardance (>100 nm) and etching rate (2 μm/min) similar to fs pulses, ps pulses are found unsuitable for bulk machining in silica glass primarily due to the build-up of a stress field causing scattering, cracks and non-homogeneous etching. Additionally, we show that the so-called "quill-effect", that is the dependence of the laser damage from the direction of writing, occurs also for ps-pulse laser machining. Finally, an opposite dependence of the retardance from the intra-pulse distance is observed for fs- and ps-laser direct writing.

Electrofluidics fabricated by space-selective metallization in glass microfluidic structures using femtosecond laser direct writing

Space-selective metallization of the inside of glass microfluidic structures using femtosecond laser direct-write ablation followed by electroless plating is demonstrated. Femtosecond laser direct writing followed by thermal treatment and successive chemical etching allows us to fabricate three-dimensional microfluidic structures inside photosensitive glass. Then, femtosecond laser ablation followed by electroless metal plating enables flexible deposition of patterned metal films on desired locations of not only the top and bottom walls but also the sidewalls of fabricated microfluidic structures. A volume writing scheme for femtosecond laser irradiation inducing homogeneous ablation on the sidewalls of microfluidic structures is proposed for sidewall metallization. The developed technique is used to fabricate electrofluidics in which microelectric components are integrated into glass microchannels. The fabricated electrofluidics are applied to control the temperature of liquid samples in the microchannels for the enhancement of chemical reactions and to manipulate the movement of biological samples in the microscale space.

Fabrication of glass microchannels by xurography for electrophoresis applications

This communication describes a simple and cost-effective method for fabricating glass microchannels by wet chemical etching using masks made by xurography in vinyl adhesive films. Analytical performance of microfluidic devices fabricated using the new approach was evaluated by microchip electrophoresis coupled to capacitively coupled contactless conductivity detection (C(4)D) and laser-induced fluorescence (LIF) detection.

Microfluidic barcode assay for antibody-based confirmatory diagnostics

Confirmatory diagnostics offer high clinical sensitivity and specificity typically by assaying multiple disease biomarkers. Employed in clinical laboratory settings, such assays confirm a positive screening diagnostic result. These important multiplexed confirmatory assays require hours to complete. To address this performance gap, we introduce a simple 'single inlet, single outlet' microchannel architecture with multiplexed analyte detection capability. A streptavidin-functionalized, channel-filling polyacrylamide gel in a straight glass microchannel operates as a 3D scaffold for a purely electrophoretic yet heterogeneous immunoassay. Biotin and biotinylated capture reagents are patterned in discrete regions along the axis of the microchannel resulting in a barcode-like pattern of reagents and spacers. To characterize barcode fabrication, an empirical study of patterning behaviour was conducted across a range of electromigration and binding reaction timescales. We apply the heterogeneous barcode immunoassay to detection of human antibodies against hepatitis C virus and human immunodeficiency virus antigens. Serum was electrophoresed through the barcode patterned gel, allowing capture of antibody targets. We assess assay performance across a range of Damkohler numbers. Compared to clinical immunoblots that require 4-10 h long sample incubation steps with concomitant 8-20 h total assay durations; directed electromigration and reaction in the microfluidic barcode assay leads to a 10 min sample incubation step and a 30 min total assay duration. Further, the barcode assay reports clinically relevant sensitivity (25 ng ml(-1) in 2% human sera) comparable to standard HCV confirmatory diagnostics. Given the low voltage, low power and automated operation, we see the streamlined microfluidic barcode assay as a step towards rapid confirmatory diagnostics for a low-resource clinical laboratory setting.

Microfluidic Western blotting

Rapid, quantitative Western blotting is a long-sought bioanalytical goal in the life sciences. To this end, we describe a Western blotting assay conducted in a single glass microchannel under purely electronic control. The μWestern blot is comprised of multiple steps: sample enrichment, protein sizing, protein immobilization (blotting), and in situ antibody probing. To validate the microfluidic assay, we apply the μWestern blot to analyses of human sera (HIV immunoreactivity) and cell lysate (NFκB). Analytical performance advances are achieved, including: short durations of 10-60 min, multiplexed analyte detection, mass sensitivity at the femtogram level, high-sensitivity 50-pM detection limits, and quantitation capability over a 3.6-log dynamic range. Performance gains are attributed to favorable transport and reaction conditions on the microscale. The multistep assay design relies on a photopatternable (blue light) and photoreactive (UV light) polyacrylamide gel. This hydrophilic polymer constitutes both a separation matrix for protein sizing and, after brief UV exposure, a protein immobilization scaffold for subsequent antibody probing of immobilized protein bands. We observe protein capture efficiencies exceeding 75% under sizing conditions. This compact microfluidic design supports demonstration of a 48-plex μWestern blot in a standard microscope slide form factor. Taken together, the μWestern blot establishes a foundation for rapid, targeted proteomics by merging exceptional specificity with the throughput advantages of multiplexing, as is relevant to a broad range of biological inquiry.

A Microchip Device for Enhancing Capillary Zone Electrophoresis Using Pressure-Driven Backflow

A reduction in the electroosmotic flow (EOF) is often desirable in glass microchannels for realizing high resolutions in capillary zone electrophoresis (CZE). While static and dynamic coatings have been commonly employed to accomplish this goal, such chemicals can introduce unwanted interactions of the analyte molecules with the separation medium and/or channel surface. In this article, we report a microfluidic device that can enhance the resolving power of CZE analysis by generating a pressure-driven backflow in the separation channel. This backflow was generated in our current work by fabricating a shallow segment (0.5-4 μm deep) downstream of the separation duct (5 μm deep) and applying an electric field across it. A mismatch in EOF transport rate at the interface of this segment was shown to yield a pressure-gradient that counteracted electroosmosis and diminished the net fluid flow in the separation conduit by nearly an order of magnitude. Although the resulting pressure-driven backflow also somewhat increased the band broadening in the analysis channel, overall it allowed us to separate an amino acid mixture with an 8-fold higher resolution. The microchip device presented here is particularly suitable for miniaturization of the CZE method and may be easily integrated into other analytical procedures making it an attractive module for lab-on-a-chip applications.

Visualization and quantification of two-phase flow in transparent miniature packed beds

Optical microscopy was used to visualize the flow of two phases [British Petroleum (BP) oil and an aqueous surfactant phase] in confined space, three-dimensional, transparent, natural porous media. The porous media consisted of water-wet cryolite grains packed inside cylindrical, glass microchannels, thus producing microscopic packed beds. Primary drainage of BP oil displacing an aqueous surfactant phase was studied at capillary numbers that varied between 10(-6) and 10(-2). The confinement space had a significant effect on the flow behavior. Phenomena of burst motion and capillary fingering were observed for low capillary numbers due to the domination of capillary forces. It was discovered that breakthrough time and capillary number bear a log-log scale linear relationship, based on which a generalized correlation between oil travel distance x and time t was found empirically.

Effect of PVP on the electroosmotic mobility of wet‐etched glass microchannels

We present an experimental study on the effect of polymer PVP on EOF mobility of microchannels wet etched into optical white soda lime glass, also known as Crown glass. We performed experiments to evaluate the effect of PVP concentration and pH on EOF mobility. We used on-chip capillary zone electrophoresis and a neutral fluorescent dye as a passive marker to quantify the electroosmotic flow. We performed experiments under controlled conditions by varying pH from 5.2 and 10.3 and concentration of PVP from 0 to 2.0% w/w at constant ionic strength (30 mM). Our experiments show that PVP at concentrations of 1.0% or above very effectively suppress EOF at low pH (6.6). At high pH of 10.3, PVP has a much weaker suppressing effect on EOF and increasing its concentration above about 0.5% showed negligible effect on EOF mobility. Finally, we briefly discuss the effects of pH on using PVP as an adsorbed coating. Our experiments provide useful guidelines on choosing correct pH and concentration of PVP for effective EOF suppression in glass channels.

Analytical detection of biological thiols in a microchip capillary channel

Sulfur-containing amino acids, such as cysteine and homocysteine play crucial roles in biological systems for the diagnosis of medical states. In this regard, this paper deals with separation, aliquot and detection of amino thiols on a microchip capillary electrophoresis with electrochemical detection in an inverted double Y-shaped microchannel. Unlike the conventional capillary electrophoresis, the modified microchannel design helps in storing the separated thiols in different reservoirs for further analysis, if required; and also eliminates the need of electrodes regeneration. The device was fabricated using conventional photolithographic technique which consisted of gold microelectrodes on a soda lime glass wafer and microchannels in PDMS mold. Multiple detections were performed using in-house fabricated dual potentiostat. Based on amperometric detection, cysteine and homocysteine were analyzed in 105s and 120s, respectively after diverting in branched channels. Repeated experiments proved the good reproducibility of the device. The device produced a linear response for both cysteine and homocysteine in electrochemical analysis. To prove the practicality of device, we also analyzed cysteine and homocysteine in real blood samples without any pre-treatment. Upon calculation, the device showed a very low limit of detection of 0.05μM. The modified microchip design shall find a broad range of analytical applications involving assays of thiols and other biological compounds.

Enhanced depth control of ultrafast laser micromachining of microchannels in soda-lime glass

Femtosecond laser micromachining has progressed considerably in the last decade due to the increasing interest in glass microsystems. In this work, we present a systematic study of the femtosecond laser ablation rate of soda-lime glass as a function of the deposited energy and pulse overlapping parameters. Experimental results demonstrate that the incubation effect reported by other authors can be neglected for particular process conditions and a constant ablation rate can be obtained, thus enhancing the depth control of the fabricated features.

Depth measurement in fully enclosed microchannels using laser interferometry

A cost-effective characterization technique for the measurement of depth in fully enclosed, optically transparent microchannels is described. The technique is suitable for depth measurement in xurographic microchannels, which are increasingly being used in microfluidic and bioengineering applications. The principle of interference is utilized in a basic laboratory setup that does not require calibration. The limitation on specimen size typically imposed due to the short working distances in commercial interferometers is eliminated. The interferometric technique is capable of characterizing glass microchannels with dimensions of the order of 100 µm. The measurement relative uncertainty is approximately 0.3%. The method provides a means to characterize microchannel height (or depth) in use when adhesives used in assembly, or pressure differences due to external clamping or high internal pressures, distort the microchannel dimensions from their as-fabricated values.

High-throughput rear-surface drilling of microchannels in glass based on electron dynamics control using femtosecond pulse trains

This study proposes a rear-surface ablation enhancement approach to fabricate high-aspect-ratio microchannels by temporally shaping femtosecond laser pulse trains. In the case study of K9 glass, enhancements of up to a 56 times higher material removal rate and a three times greater maximum drilling depth are obtained by the proposed method, as compared with conventional femtosecond laser drilling at the same processing parameters. The improvements are due to the changes of photon-electron interactions by shaping femtosecond pulse train, which can effectively adjust the photon absorption and localized transient material properties by changing electron dynamics such as free electron densities.

Mixing patterns in water plugs during water/ionic liquid segmented flow in microchannels

Circulation patterns and mixing characteristics within water plugs in liquid/liquid segmented flow were investigated by means of micro-Particle Image Velocimetry. Experiments were carried out in a glass microchannel with circular cross-section of 100μm radius using [C4mim][NTf2] ionic liquid as the carrier fluid. A T-junction was used as inlet, while mixture velocities varied from 0.0028m/s to 0.0674m/s. Two main circulation vortices were found within the plugs while at intermediate mixture velocities two additional secondary vortices appeared at the plug front. The mixing rate was locally quantified by means of the non-dimensional circulation time, which was calculated across the plug length. Consistently with the circulation patterns, the non-dimensional circulation time was found to have a profile along the direction of the flow that mirrors the shape of the plug, with a minimum at the axial location of the vortex cores (where the circulation velocity is maximum at the channel centre) while it tended to infinity towards the liquid/liquid interfaces. For all the experiments the minimum value of the circulation time fell within the range of 1.00–1.75. For increasing mixture velocities (i.e. increasing Ca) and sufficiently long plugs (εIL=0.4) a general decrease (i.e. higher mixing rate) of the circulation time minimum was found, although the behaviour was rather complex. On the other hand, the circulation velocity linearly increased as the Ca number (mixture velocity) increased.

Liquid–Liquid Two-Phase Flow Patterns in a Serpentine Microchannel

Liquid–liquid two-phase flow patterns in a serpentine glass microchannel have been studied using a camera with very high shutter speed. The phase system is equilibrated water−succinic acid−n-butanol system. Observed flow patterns have been classified into seven different types: slug flow, slug and droplet flow, droplet flow, unstable annular flow, annular flow, annular dispersed flow, and fully dispersed flow. Two different ways of introducing the aqueous and organic phases into the microchannel have been studied. Flow regime maps are presented and discussed. Voronoi diagrams of the flow regime maps are also presented.

901 超硬合金金型の微細溝研削加工に関する研究 : 加工条件が研削特性に及ぼす影響

Microchannel chips for use in micro total analysis systems have recently been attracting attention in the medical field. Generally, microchannel chips are composed of plastic Or glass. Glass is strong in terms of heat and chemical erosion resistance, whereas plastic is weak. However, dies for manufacturing glass microchannel chips are currently not viable because they are composed of cemented carbide. Therefore, in this study, to manufacture cemented carbide microchannel chip dies, we examine methods of forming a fine groove by means of grinding using an electrodeposited diamond wheel. The results of the study clarify the relationship among machining condition, surface roughness, deviation of groove shape and groove depth.

1019 気液固混相反応に用いる触媒充填型ガラス製マイクロ流路デバイスの開発(OS8-2 オーガナイズドセッション《マイクロマシンとG-MEMS/N-MEMS》)

Hydrogen peroxide (H_2O_2) is a chemical which has a wide variety of applications. The direct synthesis of hydrogen peroxide from hydrogen and oxygen gas is a potential process which does not require complicated operations and much energy, moreover, the commercialization of the process has been strongly desired. Before this study, we have designed and fabricated a glass micro-channel reactor for the direct synthesis of hydrogen peroxide. Then in order to determine the flow of calm region, the climacteric region and the instability region when gas-liquid coexist on catalyst packed-bed, we observed the flow of gas-liquid (N_2-H_2O) coexistence in fabricated reactor (1 channel). Furthermore, the pressure drop of gas-liquid on catalytic packed-bed was measured.