Planar Microfluidic Devices Research Articles

Tandem sulfur chemiluminescence and flame ionization detection with planar microfluidic devices for the characterization of sulfur compounds in hydrocarbon matrices

The detection of sulfur compounds in different hydrocarbon matrices, from light hydrocarbon feedstocks to medium synthetic crude oil feeds provides meaningful information for optimization of refining processes as well as demonstration of compliance with petroleum product specifications. With the incorporation of planar microfluidic devices in a novel chromatographic configuration, sulfur compounds from hydrogen sulfide to alkyl dibenzothiophenes and heavier distributions of sulfur compounds over a wide range of matrices spanning across a boiling point range of more than 650°C can be characterized, using one single analytical configuration in less than 25min. In tandem with a sulfur chemiluminescence detector for sulfur analysis is a flame ionization detector. The flame ionization detector can be used to establish the boiling point range of the sulfur compounds in various hydrocarbon fractions for elemental specific simulated distillation analysis as well as profiling the hydrocarbon matrices for process optimization. Repeatability of less than 3% RSD (n=20) over a range of 0.5–1000 parts per million (v/v) was obtained with a limit of detection of 50 parts per billion and a linear range of 0.5–1000 parts per million with a correlation co-efficient of 0.998.

Multidimensional gas chromatography using microfluidic switching and low thermal mass gas chromatography for the characterization of targeted volatile organic compounds

Volatile organic compounds such as light hydrocarbons, dienes, and aromatic compounds are often encountered in the manufacturing and processing environments of chemical and petrochemical segments. These compounds need to be closely monitored for process optimization, plant maintenance and industrial hygiene purposes. A high throughput analytical approach has been successfully developed and implemented for the accurate measurement of fourteen commonly encountered analytes. The approach incorporates a recently introduced 5-port planar microfluidic device configured for use as a Deans switch for multidimensional gas chromatography. The use of multidimensional gas chromatography allows the elimination of potential chromatographic contaminants with a substantial enhancement of stationary phase selectivity via the use of columns with different separation mechanisms, and the back-flushing of heavier undesired hydrocarbons. A low thermal mass gas chromatographic module was employed in the second dimension of the two-dimensional gas chromatography system and was used to provide independent temperature control, and rapid heating and cooling to meet the high throughput requirements. By successfully combining these concepts, complete analysis of fourteen targeted components can be conducted in less than 120s. Repeatability of retention times for all compounds was found to be less than 0.05% (n=20). Repeatability of area counts at two levels, namely 10ppmv and 1000ppmv over a period of two days was found to be less than 3% (n=20). Apart from methane, which has a detection limit of 0.4ppmv, the rest of the compounds were found to have detection limits of less than 0.2ppmv. Compounds of interest were found to be linear over a range of 500ppbv–3000ppmv with correlation coefficients greater than 0.999.

Planar microfluidic devices in flow modulated comprehensive two dimensional gas chromatography for challenging petrochemical applications

Two three-port planar microfluidic devices are successfully configured for use as a modulator to carry out flow modulated comprehensive two-dimensional gas chromatography. A low thermal mass column module is employed to provide independent temperature control for each separation dimension in the analytical system in some of the applications described. The utility of the analytical system is demonstrated with a number of difficult petrochemical applications comprising analytes that possess a wide range of boiling points; from natural gas to crude oil. A variety of columns with different selectivities and separation mechanisms in the categories of porous layer open tubular and wall-coated open tubular are employed for the applications described.

Magnetic concentration of particles and cells in ferrofluid flow through a straight microchannel using attracting magnets

Concentrating particles to a detectable level is often necessary in many applications. Although magnetic force has long been used to enrich magnetic (or magnetically tagged) particles in suspensions, magnetic concentration of diamagnetic particles is relatively new and little reported. We demonstrate in this work a simple magnetic technique to concentrate polystyrene particles and live yeast cells in ferrofluid flow through a straight rectangular microchannel using negative magnetophoresis. The magnetic field gradient is created by two attracting permanent magnets that are placed on the top and bottom of the planar microfluidic device and held in position by their natural attractive force. The magnet–magnet distance is mainly controlled by the thickness of the device substrate and can be made small, allowing for the use of a dilute ferrofluid in the developed magnetic concentration technique. This advantage not only enables a magnetic/fluorescent label-free handling of diamagnetic particles, but also renders such handling biocompatible.

Applications of planar microfluidic devices and gas chromatography for complex problem solving

The application of planar microfluidic devices in GC for the separation of components of interest otherwise difficult to separate in a single analysis is presented. A variety of configurations were used for parallel chromatography, column effluent splitting, back flushing, selectivity tuning, valve less switching and column isolation, heart cutting, and comprehensive multidimensional chromatography. The synergies of recently commercialized planar microfluidic devices combined with the resolving power of fused-silica capillary columns are demonstrated. Difficult separations were accomplished in one single analysis, such as light hydrocarbons in air with high-moisture content, fixed gases in hydrocarbons, trace sulfur containing compounds in natural gas, and oxygenated compounds in hydrocarbons, among others.

Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n=20). Reproducibility of area counts at two levels, namely 100ppmv and 1000ppmv over a period of two days were found to be less than 5.5% (n=20). Oxygen and nitrogen were found to be linear over a range from 20ppmv to 10,000ppmv with correlation coefficients of at least 0.998 and detection limits of less than 10ppmv. Hydrocarbons of interest were found to be linear over a range from 200ppbv to 1000ppmv with correlation coefficients of greater than 0.999 and detection limits of less than 100ppbv.

The design of microfluidic affinity chromatography systems for the separation of bioanalytes

The analytical (numerical) design of planar microfluidic affinity chromatography devices, which consist of multiple separation lanes and multiple, different surface-immobilised receptor patterns in each lane, is described. The model is based on the analytical solution of the transport-reaction equations in microfluidic systems of low Gratz number and for injection of small analyte plugs. The results reveal a simple approach for the design of microfluidic affinity chromatography devices tailored to the separation of bioanalytes, where receptors with high binding affinity are available. These devices have been designed for bioanalytical applications in mind, most notably for the proteomics field; the results are illustrated with an example using β-Amyloid binding peptides.

Multi-dimensional gas chromatography with a planar microfluidic device for the characterization of volatile oxygenated organic compounds

Oxygenated compounds like methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetaldehyde, crotonaldehyde, ethylene oxide, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, and 2-chloromethyl-1,3-dioxolane are commonly encountered in industrial manufacturing processes. Despite the availability of a variety of column stationary phases for chromatographic separation, it is difficult to separate these solutes from their respective matrices using single dimension gas chromatography. Implemented with a planar microfluidic device, conventional two-dimensional gas chromatography and the employment of chromatographic columns using dissimilar separation mechanisms like that of a selective wall-coated open tubular column and an ionic sorbent column have been successfully applied to resolve twelve industrially significant volatile oxygenated compounds in both gas and aqueous matrices. A Large Volume Gas Injection System (LVGIS) was also employed for sample introduction to enhance system automation and precision. By successfully integrating these concepts, in addition to having the capability to separate all twelve components in one single analysis, features associated with multi-dimensional gas chromatography like dual retention time capability, and the ability to quarantine undesired chromatographic contaminants or matrix components in the first dimension column to enhance overall system cleanliness were realized. With this technique, a complete separation for all the compounds mentioned can be carried out in less than 15min. The compounds cited can be analyzed over a range of 250ppm (v/v) to 100ppm (v/v) with a relative standard deviation of less than 5% (n=20) with high degree of reliability.

Drop formation in non-planar microfluidic devices

Microfluidic devices can be used to produce single or multiple emulsions with remarkably precise control of both the contents and size of the drops. Since each level of a multiple emulsion is formed by a distinct fluid stream, very efficient encapsulation of materials can be achieved. To obtain high throughput, these devices can be fabricated lithographically, allowing many devices to operate in parallel. However, to form multiple emulsions using a planar microfluidic device, the wettability of its surface must switch from hydrophobic to hydrophilic on the scale of micrometers where the drops are formed; this makes the fabrication of the devices very difficult. To overcome this constraint, we introduce non-planar microfluidic devices with graduated thicknesses; these can make drops even when their wetting properties do not favor drop formation. Nevertheless, the dependence of drop formation on the device geometry, the flow rates and the properties of the fluids, particularly in the case of unfavorable wetting, is very complex, making the successful design of these devices more difficult. Here we show that there exists a critical value of flow of the continuous phase above which drop formation occurs; this value decreases by two orders of magnitude as the wetting to the device wall of the continuous phase improves. We demonstrate how this new understanding can be used to optimize device design for efficient production of double or multiple emulsions.

Fabrication of Lateral Porous Silicon Membranes for Planar Microfluidic Devices

Abstract In this work, we present a novel fabrication process to create lateral porous silicon membranes. The advantage of this process is to enable the monolithic integration of porous silicon directly into planar microchannels, thus greatly simplifying the integration of membranes into fluidic devices and opening doors to the use of porous silicon into planar lab-on-a-chip devices for filtering purposes. The presented fabrication technique relies on the patterning of local electrodes within microchannels to carry out silicon anodization parallel to the surface of the silicon substrate. The feasibility of our approach is demonstrated by creating 10 μm long mesoporous membranes within 3 μm deep microchannels. Our experimental results are supported by current flow studies using finite element analysis.

Low-parachor solvents extraction and thermostated micro-thin-layer chromatography separation for fast screening and classification of spirulina from pharmaceutical formulations and food samples

The goal of this paper is to demonstrate the separation and detection capability of eco-friendly micro-TLC technique for the classification of spirulina and selected herbs from pharmaceutical and food products. Target compounds were extracted using relatively low-parachor liquids. A number of the spirulina samples which originated from pharmaceutical formulations and food products, were isolated using a simple one step extraction with small volume of methanol, acetone or tetrahydrofuran. Herb samples rich in chlorophyll dyes were analyzed as reference materials. Quantitative data derived from micro-plates under visible light conditions and after iodine staining were explored using chemometrics tools including cluster analysis and principal components analysis. Using this method we could easily distinguish genuine spirulina and non-spirulina samples as well as fresh from expired commercial products and furthermore, we could identify some biodegradation peaks appearing on micro-TLC profiles. This methodology can be applied as a fast screening or fingerprinting tool for the classification of genuine spirulina and herb samples and in particular may be used commercially for the rapid quality control screening of products. Furthermore, this approach allows low-cost fractionation of target substances including cyanobacteria pigments in raw biological or environmental samples for preliminary chemotaxonomic investigations. Due to the low consumption of the mobile phase (usually less than 1 mL per run), this method can be considered as environmentally friendly analytical tool, which may be an alternative for fingerprinting protocols based on HPLC machines and simple separation systems involving planar micro-fluidic or micro-chip devices.

Temperature-controlled micro-TLC: A versatile green chemistry and fast analytical tool for separation and preliminary screening of steroids fraction from biological and environmental samples

This paper is a continuation of our previous research focusing on development of micro-TLC methodology under temperature-controlled conditions. The main goal of present paper is to demonstrate separation and detection capability of micro-TLC technique involving simple analytical protocols without multi-steps sample pre-purification. One of the advantages of planar chromatography over its column counterpart is that each TLC run can be performed using non-previously used stationary phase. Therefore, it is possible to fractionate or separate complex samples characterized by heavy biological matrix loading. In present studies components of interest, mainly steroids, were isolated from biological samples like fish bile using single pre-treatment steps involving direct organic liquid extraction and/or deproteinization by freeze-drying method. Low-molecular mass compounds with polarity ranging from estetrol to progesterone derived from the environmental samples (lake water, untreated and treated sewage waters) were concentrated using optimized solid-phase extraction (SPE). Specific bands patterns for samples derived from surface water of the Middle Pomerania in northern part of Poland can be easily observed on obtained micro-TLC chromatograms. This approach can be useful as simple and non-expensive complementary method for fast control and screening of treated sewage water discharged by the municipal wastewater treatment plants. Moreover, our experimental results show the potential of micro-TLC as an efficient tool for retention measurements of a wide range of steroids under reversed-phase (RP) chromatographic conditions. These data can be used for further optimalization of SPE or HPLC systems working under RP conditions. Furthermore, we also demonstrated that micro-TLC based analytical approach can be applied as an effective method for the internal standard (IS) substance search. Generally, described methodology can be applied for fast fractionation or screening of the whole range of target substances as well as chemo-taxonomic studies and fingerprinting of complex mixtures, which are present in biological or environmental samples. Due to low consumption of eluent (usually 0.3–1 mL/run) mainly composed of water–alcohol binary mixtures, this method can be considered as environmentally friendly and green chemistry focused analytical tool, supplementary to analytical protocols involving column chromatography or planar micro-fluidic devices.

Liquid–liquid fluorescent waveguides using microfluidic-drifting-induced hydrodynamic focusing

We demonstrate fluorescent liquid-core/liquid-cladding (L 2) waveguides focused in three-dimensional (3-D) space based on a 3-D hydrodynamic focusing technique. In the proposed system, the core and vertical cladding streams are passed through a curved 90° corner in a microfluidic channel, leading to the formation of a pair of counter rotating vortices known as the Dean vortex. As a result, the core fluid is completely confined within the cladding fluid and does not touch the top and bottom poly(dimethylsiloxane) (PDMS) surfaces of the microfluidic channel. Because the core stream was not in contact with the PDMS channel, whose refractive index contrast and optical smoothness with the core fluid are lower than that between the core and the cladding fluids, the 3-D focused L 2 waveguide exhibited a higher captured fraction (η) and lower propagation loss when compared to conventional two-dimensional (2-D) focused L 2 waveguides. Because the proposed 3-D focused L 2 waveguides can be generated in planar PDMS microfluidic devices, such optofluidic waveguides can be integrated with precise alignment together with other in-plane microfluidic and optical components to achieve micro-total analysis systems (μ-TAS).

The importance of downstream events in microfluidic viscoelastic entry flows: Consequences of increasing the constriction length

Polymer solutions and melts can exhibit large upstream corner and lip vortices, unstable and diverging flow and an enhanced pressure drop when flowing through a geometry containing a constriction. In the present work, we use a planar microfluidic device to show that the length of the downstream constriction plays an important role in the upstream kinematics and the extra pressure drop. That is, the elastic flow phenomena observed upstream of a constriction during entry flows of polymer solutions are not exclusively a result of the stretching dynamics induced by the converging flow—the downstream relaxation events are, at least, equally important. Flow visualization experiments with semi-dilute solutions of a high molecular weight polymer showed that large stable symmetric vortices could be reduced to highly chaotic asymmetric flow, merely by increasing the length of the constriction—the Reynolds number and elasticity number were both held constant. This was accompanied by a higher extra pressure. These results support the hypothesis that elastic flow instabilities originate downstream of the constriction (at the expansion) and move progressively upstream with time and/or flowrate. These findings may also partly explain the discrepancies commonly observed between the results of entry flow experiments and numerical simulations, in which the downstream geometry is very rarely considered. Lastly, we illustrate how to minimize the occurrence of unstable flow upstream of a constriction, which is a necessary condition for closed microrheometry devices used to characterize low viscosity elastic fluids.

A microflow chemiluminescence system for determination of chloramphenicol in honey with preconcentration using a molecularly imprinted polymer

A novel chemiluminescence (CL) microfluidic system incorporating a molecularly imprinted polymer (MIP) preconcentration step was used for the determination of chloramphenicol in honey samples. The MIP was prepared by using chloramphenicol as the template, diethylaminoethyl methacrylate (DAM) as the function monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linking monomer, 2, 2′-dimethoxy-2-phenylacetophenone (DMPA) as the free radical initiator and toluene and dodecanol as the solvent. The MIP was pre-loaded into a 10 mm long, 2 mm wide and 150 μm deep channel in a planar glass microfluidic device. When the sample containing chloramphenicol was introduced into the microfluidic device it was first preconcentrated on the MIP then detected by an enhancement effect on the chemiluminescence reaction of tris(2, 2′-bipyridyl) ruthenium(II) with cerium(IV) sulphate in sulphuric acid. A micro-syringe pump was used to pump the reagents. The CL intensity was linear in relationship to the chloramphenicol concentrations from 1.55 × 10 −4 to 3.09 × 10 −3 μmol L −1 ( r 2 = 0.9915) and the detection limit (3 σ) and the quantitation limit (10 σ) were found to be 7.46 × 10 −6 and 2.48 × 10 −5 μmol L −1, respectively. This method offered a high selectivity and sensitivity for quantitative analysis of chloramphenicol in the honey samples.

Single-layer planar on-chip flow cytometer using microfluidic drifting based three-dimensional (3D) hydrodynamic focusing

In this work, we demonstrate an on-chip microfluidic flow cytometry system based on a three-dimensional (3D) hydrodynamic focusing technique, microfluidic drifting. By inducing Dean flow in a curved microfluidic channel, microfluidic drifting can be used to hydrodynamically focus cells or particles in the vertical direction and enables the 3D hydrodynamic focusing in a single-layer planar microfluidic device. Through theoretical calculation, numerical simulation, and experimental characterization, we found that the microfluidic drifting technique can be effectively applied to three-dimensionally focus microparticles with density and size equivalent to those of human CD4+ T lymphocytes. In addition, we developed a flow cytometry platform by integrating the 3D focusing device with a laser-induced fluorescence (LIF) detection system. The system was shown to provide effective high-throughput flow cytometry measurements at a rate of greater than 1700 cells s(-1).

Refractive index measurements in a shallow multichannel microfluidic system

Thin film interference of monochromatic radiation in transparent films is used extensively as a non-destructive technique to determine film thickness over extended surface areas. This approach may also be used with liquids where reflection at solid/liquid/solid interfaces creates an interference pattern, dependent on the liquid refractive index. Such a system facilitates refractive index measurements in low volume (nanolitre) samples, without the need for high-index structured materials forming waveguide layers. We use a planar multichannel microfluidic device fabricated with a standard photolithography technique and demonstrate its suitability for nanolitre refractive index measurements. Liquids of varied refractive indices from 1.33 to 1.35 were evaluated in the microfluidic channel, indicating a limit of detection 10−6 refractive index unit (RIU), illustrating how this approach can simultaneously monitor a number of transparent and weakly absorbing liquid samples.

Influence of channel position on sample confinement in two-dimensional planar microfluidic devices

We report enhanced sample confinement on microfluidic devices using a combination of electrokinetic flow from adjacent control channels and electric field shaping with an array of channels perpendicular to the sample stream. The basic device design consisted of a single first dimension (1D) channel, intersecting an array of 32 or 96 parallel second dimension (2D) channels. To minimize sample dispersion and leakage into the parallel channels as the sample traversed the sample transfer region, control channels were placed to the left and right of the 1D and waste channels. The electrokinetic flow from the control channels confined the sample stream and acted as a buffer between the sample stream and the 2D channels. To further enhance sample confinement, the electric field was shaped parallel to the sample stream by placing the channel array in close proximity to the sample transfer region. Using COMSOL Multiphysics, initial work focused on simulating the electric fields and fluid flows in various device geometries, and the results guided device design. Following the design phase, we fabricated devices with 40, 80, and 120 microm wide control channels and evaluated the sample stream width as a function of the electric field strength ratio in the control and 1D channels (E(C)/E(1D)). For the 32 channel design, the 40 and 80 microm wide control channels produced the most effective sample confinement with stream widths as narrow as 75 microm, and for the 96 channel design, all three control channel widths generated comparable sample stream widths. Comparison of the 32 and 96 channel designs showed sample confinement scaled easily with the length of the sample transfer region.

High resolution DNA separations using microchip electrophoresis

Planar microfluidic devices have emerged as effective tools for the electrophoretic separation of a variety of different DNA inputs. The advancement of this miniaturized platform was inspired initially by demands placed on electrophoretic performance metrics by the human genome project and has provided a viable alternative to slab gel and even capillary formats due to its ability to offer high resolution separations of nucleic acid materials in a fraction of the time associated with its predecessors, consumption of substantially less sample and reagents while maintaining the ability to perform many separations in parallel for realizing ultra-high throughputs. Another compelling advantage of this separation platform is that it offers the potential for integrating front-end sample preprocessing steps onto the separation device eliminating the need for manual sample handling. This review aims to compile a recent survey of various electrophoretic separations using either glass or polymer-based microchips in the areas of genotyping and DNA sequencing as well as those involving the growing field of DNA-based forensics.

Organic transistor based circuit as drive for planar microfluidic devices

Organic transistor based circuits are a promising candidate for acting as drivers for microfluidic devices handling discrete droplets. The ease of fabrication along with the ability to generate desired voltage levels for performing electrowetting based actuation of liquids make them an ideal match for discrete droplet based microfluidic systems. In this article, we report the implementation of an organic transistor based complementary metal-oxide semiconductor (CMOS) inverter used to actuate microliter quantities of droplets on a simple planar microfluidic device. We also present two approaches for fabricating an open-structured device for different applications. The inverter is fabricated using Pentacene and N, N′- bis (n-octyl) dicyanoperylene-3, 4:9, 10-bis (dicarboxyimide) (PDI-8CN2) (Northwestern University). The inverter output is stable and repeatable and is used to actuate droplets over adjacent electrodes as well as in merging of discrete droplets.