A water-activated pump for portable microfluidic applications

An on-chip micropump for portable microfluidic applications was investigated using mathematical modeling and experimental testing. This micropump is activated by the addition of water, via a dropper, to ionic polymer particles that swell due to osmotic effects when wetted. The resulting particle volume increase deflects a membrane, forcing a separate fluid from an adjacent reservoir. The micropump components, along with the microfluidic components, are fabricated using the contact liquid photolithographic polymerization (CLiPP) method. The maximum flow rate achieved with this pump is 17 microL per minute per mg of dry polymer particles of 355-425 microm in diameter. The pump flow rate may be controlled by adjusting the particle size and amount, the membrane properties, and the channel dimensions. The experimental results demonstrate good agreement with an analytical model describing the particle swelling and its coupling with resistive forces from the bending membrane, viscous flow in the microchannel, and interfacial effects. Key features of this micropump are that it can be placed directly on a microdevice, and that it requires only a small amount of water and no external power supply to function. Therefore, this pumping system is useful for applications in which a highly portable device is required.     

On‐chip pressure generation using a gel membrane fabricated outside of the microfluidic network

On‐chip generation of pressure gradients via electrokinetic means can offer several advantages to microfluidic assay design and operation in a variety of applications. In this article, we describe a simple approach to realizing this capability by employing a polyacrylamide‐based gel structure fabricated within a fluid reservoir located at the terminating end of a microchannel. Application of an electric field across this membrane has been shown to block a majority of the electroosmotic flow generated within the open duct yielding a high pressure at the channel–membrane junction. Experiments show the realization of higher pressure‐driven velocities in an electric field‐free separation channel integrated to the micropump with this design compared to other similar micropumps described in the literature. In addition, the noted velocity was found to be less sensitive to the extent of Debye layer overlap in the channel network, and therefore more impressive when working with background electrolytes having higher ionic strengths. With the current system, pressure‐driven velocities up to 3.6 mm/s were realized in a 300‐nm‐deep separation channel applying a maximum voltage of 3 kV at a channel terminal. To demonstrate the separative performance of our device, a nanofluidic pressure‐driven ion‐chromatographic analysis was subsequently implemented that relied on the slower migration of cationic analytes relative to the neutral and anionic ones in the separation channel likely due to their strong electrostatic interaction with the channel surface charges. A mixture of amino acids was thus separated with resolutions greater than those reported by our group for a similar analysis previously.     

An actuated pump on-chip powered by cultured cardiomyocytes

Cellular functions are frequently exploited as processing components for integrated chemical systems such as biochemical reactors and bioassay systems. Here, we have created a new cell-based microsystem exploiting the intrinsic pulsatile mechanical functions of cardiomyocytes to build a cellular micropump on-chip using cardiomyocyte sheets as prototype bio-microactuators. We first demonstrate cell-based control of fluid motion in a model microchannel without check valves and evaluate the potential performance of the bio-actuation. For this purpose, a poly(dimethylsiloxane) (PDMS) microchip with a microchannel equipped with a diaphragm and a push-bar structure capable of harnessing collective cell fluid mechanical forces was coupled to a cultured pulsating cardiomyocyte sheet, activating cell-based fluid movement in the microchannel by actuating the diaphragm. Cell oscillation frequency and correlated fluid displacement in this system depended on temperature. When culture temperature was increased, collective cell contraction frequency remained cooperative and synchronous but increased, while displacement was slightly reduced. We then demonstrated directional fluid pumping within microchannels using cantilever-type micro-check valves made of polyimide. A directional flow rate of nL min(-1) was produced. This cell micropump system could be further developed as a self-actuated and efficient mechanochemical transducer requiring no external energy sources for various purposes in the future.     

Combination of large‐volume sample stacking with an electroosmotic flow pump with field‐amplified sample injection on cross‐channel chips

A combination of two online sample concentration techniques, large‐volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) and field‐amplified sample injection (FASI), was investigated in microchip electrophoresis (MCE) to achieve highly sensitive analysis. By applying reversed‐polarity voltages on a cross‐channel microchip, anionic analytes injected throughout a microchannel were first concentrated on the basis of LVSEP, followed by the electrokinetic stacking injection of the analytes from a sample reservoir by the FASI mechanism. As well as the voltage application, a pressure was also applied to the sample reservoir in LVSEP‐FASI. The applied pressure generated a counter‐flow against the EOF to reduce the migration velocity of the stacked analytes, especially around the cross section of the microchannel, which facilitated the FASI concentration. At the hydrodynamic pressure of 15 Pa, 4520‐fold sensitivity increase was obtained in the LVSEP‐FASI analysis of a standard dye, which was 33‐times higher than that obtained with a normal LVSEP. Furthermore, the use of the sharper channel was effective for enhancing the sensitivity, e.g., 29 100‐fold sensitivity increase was achieved with the 75‐μm wide channel. The developed method was applied to the chiral analysis of amino acids in MCE, resulting in the sensitivity enhancement factor of 2920 for the separated d ‐leucine.     

An effervescent reaction micropump for portable microfluidic systems

A water-activated, effervescent reaction was used to transport fluid in a controllable manner on a portable microfluidic device. The reaction between sodium bicarbonate and an organic acid, tartaric acid and/or benzoic acid, was modeled to analyze methods of controlling the generation of carbon-dioxide gas for the purposes of pumping fluids. Integration and testing of the effervescent reaction pump in a microfluidic device was made possible by using elastomeric polymers as both photopolymerizable septa and removable lids. These materials combined to enable facile access to otherwise gas-tight devices. Based on theoretical predictions for 0.33 mg of sodium bicarbonate and a stoichiometric amount of organic acid, the pumping flow rate could be varied from 0.01 microL s(-1) to 70 microL s(-1). The flow rate is controlled by adjusting any or all of the particle size of the least soluble reactant, the amount of reactants used, and the type of organic acid selected. The tartaric acid systems rapidly produce carbon dioxide; however, the gas generation rates dramatically decrease over the course of the reaction. In contrast, carbon dioxide production rate in the benzoic acid systems is lower and nearly constant for several minutes. Water activation and direct placement on a microfluidic device are key features of this micropump, which is therefore useful for portable microfluidic applications.     

Rapid Determination of Free Amino Acids in Milk by Microchip Electrophoresis Coupled with Laser‐induced Fluorescence Detection

A simple and sensitive method for determination of free amino acids in milk by microchip electrophoresis (MCE) coupled with laser‐induced fluorescence (LIF) detection was developed. Seven kinds of standard amino acids were derivated with sulfoindocyanine succinimidyl ester (Cy5) and then perfectly measured by MCE‐LIF within 150 s. The parameters of MCE separation were carefully investigated to obtain the optimal conditions: 100 mmol·L^?1 sodium borate solution (pH 10.0) as running buffer solution, 0.8 kV as injection voltage, 2.2 kV as separation voltage etc. The linear range of the detection of amino acids was from 0.01 µmol·L^?1 to 1.0 µmol·L^?1 and the detection limit was as low as about 1.0 nmol·L^?1. This MCE‐LIF method was applied to the measurements of free amino acids in actual milk samples and satisfactory experimental results were achieved.     

A single standard calibration module for flow analysis systems based on solenoid microdevices

Only two computer-controlled microsolenoid devices, namely two micropumps or one micropump and one microvalve, are sufficient for the construction of on-line dilution modules useful in several flow analytical systems for the calibration using single standard. Three simple constructions of such modules were tested and compared. The most promising is the one based on the concept of a microvalve controlling dilution ratio of the standard and a solenoid micropump playing a double role: solution pumping device and mixing segments homogenizer. All investigated modules were tested with paired emitter detector diode (PEDD) as photometric flow-through detector and bromothymol blue as a model analyte. The best module was implemented into more advanced flow-injection system dedicated for optical detection of alkaline phosphatase activity using UV-PEDD-based flow-through detector for the enzyme reaction product.     

Rapid microarray processing using a disposable hybridization chamber with an integrated micropump

We present a disposable microarray hybridization chamber with an integrated micropump to speed up diffusion based reaction kinetics by generating convective flow. The time-to-result for the hybridization reaction was reduced from 60 min (standard protocol) down to 15 min for a commercially available microarray. The integrated displacement micropump is pneumatically actuated. It includes two active microvalves and is designed for low-cost, high volume manufacturing. The setup is made out of two microstructured polymer parts realized in polycarbonate (PC) separated by a 25 μm thermoplastic elastomer (TPE) membrane. Pump rate can be controlled between 0.3 μl s(-1) and 5.7 μl s(-1) at actuation frequencies between 0.2 Hz and 8.0 Hz, respectively.     

Effects of 3D electrodes arrangement in a novel AC electroosmotic micropump: Numerical modeling and experimental validation

To date, a comprehensive systematic optimization framework, capable of accurately predicting an efficient electrode geometry, is not available. Here, different geometries, including 3D step electrodes, have been designed in order to fabricate AC electroosmosis micropumps. It is essential to optimize both geometrical parameters of electrode, such as width and height of steps on each base electrode and their location in one pair, the size of each base electrode (symmetric or asymmetric), the gap of electrode pairs, and nongeometrical parameters such as fluid flow in a channel and electrical characteristics (e.g., frequency and voltage). The governing equations comprising of electric domain and fluid domain have been coupled using finite element method. The developed model was employed to investigate the effect of electrode geometric parameters on electroosmotic slip velocity and its subsequent effect on pressure and flow rate. Numerical simulation indicates that the optimal performance can be achieved using a design with varying step height and displacement, at a given voltage (2.5 V) and frequency (1 kHz). Finally, in order to validate the numerical simulation, the optimal microchip was fabricated using a combination of photolithography, electroplating, and a polydimethylsiloxane microchannel. Our results indicate that our micropump is capable of generating a pressure, velocity, and flow rate of 74.2 Pa, 1.76 mm/s, and 14.8 µl/min, respectively. This result reveals that our proposed geometry outperforms the state-of-the-art micropumps previously reported in the literature by improving the fluid velocity by 32%, with 80% less electrodes per unit length, and whereas the channel length is ∼80% shorter.     

Bi‐directional ACET micropump for on‐chip biological applications

The ability to control and pump high ionic strength fluids inside microchannels forms a major advantage for clinical diagnostics and drug screening processes, where high conductive biological and physiological buffers are used. Despite the known potential of AC electro‐thermal (ACET) effect in different biomedical applications, comparatively little is known about controlling the velocity and direction of fluid inside the chip. Here, we proposed to discretize the conventional electrodes to form various asymmetric electrode structures in order to control the fluid direction by simple switching the appropriate electric potential applied to the discretized electrodes. The ACET pumping effect was numerically studied by solving electrical, thermal and hydrodynamic multi‐physic coupled equations to optimize the geometrical dimensions of the discretized system. PBS solutions with different ionic strength were seeded with 1 μm sized fluorescent particles and electrothermally driven fluid motion was observed inside the channel for different electrode structures. Experimental analyses confirm that the proposed micropump is efficient for a conductivity range between 0.1 and 1 S/m and the efficiency improves by increasing the voltage amplitude. Behavior of the proposed electrode–electrolyte system is discussed by lumped circuit model. Frequency response of system illustrated that the optimal frequency range increases by increasing the conductivity of medium. For 0.18 S/m PBS solution, the constant pumping effect was observed at frequency range between 100 kHz and 1 MHz, while frequency range of 100 kHz to 5 MHZ was observed for 0.42 S/m. The characteristics of experimental results were in good agreement with the theoretical model.     

Investigation of pumping mechanism for non‐Newtonian blood flow with AC electrothermal forces in a microchannel by hybrid boundary element method and immersed boundary‐lattice Boltzmann method

Efficient pumping of blood flow in a microfluidic device is essential for rapid detection of bacterial bloodstream infections (BSI) using alternating current (AC) electrokinetics. Compared with AC electro‐osmosis (ACEO) phenomenon, the advantage of AC electrothermal (ACET) mechanism is its capability of pumping biofluids with high electrical conductivities at a relatively high AC voltage frequency. In the current work, the microfluidic pumping of non‐Newtonian blood flow using ACET forces is investigated in detail by modeling its multi‐physics process with hybrid boundary element method (BEM) and immersed boundary‐lattice Boltzmann method (IB‐LBM). The Carreau–Yasuda model is used to simulate the realistic rheological behavior of blood flow. The ACET pumping efficiency of blood flow is studied in terms of different AC voltage magnitudes and frequencies, thermal boundary conditions of electrodes, electrode configurations, channel height, and the channel length per electrode pair. Besides, the effect of rheological behavior on the blood flow velocity is theoretically analyzed by comparing with the Newtonian fluid flow using scaling law analysis under the same physical conditions. The results indicate that the rheological behavior of blood flow and its frequency‐dependent dielectric property make the pumping phenomenon of blood flow different from that of the common Newtonian aqueous solutions. It is also demonstrated that using a thermally insulated electrode could enhance the pumping efficiency dramatically. Besides, the results conclude that increasing the AC voltage magnitude is a more economical pumping approach than adding the number of electrodes with the same energy consumption when the Joule heating effect is acceptable.     

Quantitative determination of amino acids in functional foods by microchip electrophoresis

Microchip electrophoresis (MCE), a first-generation micrototal analysis system, has emerged during the miniaturization phase of food analysis. Based on the micellar electrokinetic chromatography mode, a simple and fast MCE method with light emitting diode-induced fluorescence detection was developed for quantitative analysis of amino acids in three different kinds of functional foods, viz. sports beverages, jelly-form beverages, and tablet-form functional foods. In contrast to the glass microchip, we improved the separation of amino acids on a poly(methyl methacrylate) (PMMA) chip by addition of cationic starch derivatives. 4-fluoro-7-nitro-2,1,3-benzoxadiazole, which has a short labeling time for amino acids, was used as the fluorescently labeled dye. This MCE method takes less than 10 min of total analysis time including sample preparation and analysis of amino acids in functional foods on a PMMA chip. The results show that this approach has the potential to be a fast and simple method for amino acid analysis in functional foods.     

Ion Exchange Application of Overpressured Thin-Layer Chromatography

Abstract

The application of overpressured thin-layer chromatography introduced into the field of ion exchange chromatography. The basic differences between overpressured thin-layer chromatography and classical thin-layer chromatography are discussed including the distinction between the separations performed on thin-layer plates containing silica gel and a mixture of ion exchanger material and silica gel. The basic increase of flow velocity of solvent front with the aid of a pressurized ultra-micro chamber and the effect of flow velocity on the height equivalent of the theoretical plates are also presented. For basic amino acids, the flow velocity vs plate height curves show optima at a moderately high rate of development.     

Forensic Identification of Dyes in Ballpoint Pen Inks Using LC–ESI–MS

The aim of this work was to develop a new technique using flow injection analysis combined with LC–ESI–MS which allows identification of dyes in ballpoint pen inks. A sample preparation procedure for the extraction of dyes from ballpoint pen strokes has been developed. The characteristic group of ions for each sample of 21 studied ballpoint pen inks corresponding to the present dyes has been determined using flow injection method. LC separation conditions for identified dyes have been optimized on reversed-phase sorbent based on silica gel. The best composition of the mobile phase for the dyes mixture LC separation was 0.1% aqueous formic acid and acetonitrile. Detection of dyes was carried out using mass spectrometry with electrospray ionization in positive and negative modes after reversed-phase liquid chromatography separation. Dye composition of ink was additionally confirmed comparing the data obtained from the literature. Flow injection analysis allows obtaining intensive ions of unknown strokes. It is difficult to get this information using only chromatographic methods, because dyes peak intensity can be low and noise of basic line high. Flow injection method allows distinguishing the analyzed 21 ballpoint pens by determining a characteristic set of dyes. The developed flow injection technique is very simple and quick. As a result, a novel approach for the identification of dyes in the ballpoint pen inks by flow injection analysis with LC–ESI–MS and UV detection without using standard dye samples has been established. It can be an effective alternative to the existing LC–DAD–MS and IR spectroscopy methods.     

Remotely powered distributed microfluidic pumps and mixers based on miniature diodes

We demonstrate new principles of microfluidic pumping and mixing by electronic components integrated into a microfluidic chip. The miniature diodes embedded into the microchannel walls rectify the voltage induced between their electrodes from an external alternating electric field. The resulting electroosmotic flows, developed in the vicinity of the diode surfaces, were utilized for pumping or mixing of the fluid in the microfluidic channel. The flow velocity of liquid pumped by the diodes facing in the same direction linearly increased with the magnitude of the applied voltage and the pumping direction could be controlled by the pH of the solutions. The transverse flow driven by the localized electroosmotic flux between diodes oriented oppositely on the microchannel was used in microfluidic mixers. The experimental results were interpreted by numerical simulations of the electrohydrodynamic flows. The techniques may be used in novel actively controlled microfluidic-electronic chips.     

Quantification of taurine and amino acids in mice single fibrosarcoma cell by microchip electrophoresis coupled with chemiluminescence detection

A method based on MCE coupled with chemiluminescence (CL) detection was developed for the determination of taurine (Tau) and amino acids including alanine (Ala), glycine (Gly), tryptophan (Trp), glutamic acid (Glu) and aspartic acid (Asp) present in mice single fibrosarcoma (S180) cells. Cell injection, loading, cytolysis, electrophoretic separation and CL detection were integrated onto a simple double‐T microfluidic chip. The intracellular constituents were electrophoretically separated within 150 s. The CL detection was based on the enhancement effects of Tau and amino acids on the CL reaction of luminol with H₂O₂ and Cu²⁺. The average amounts of Tau, Trp, Gly, Ala, Glu and Asp in per S180 cell from a cell population were 4.73, 1.23, 2.65, 1.94, 1.61 and 1.99 fmol. Ten S180 cells were analyzed, and the contents of Tau, Trp, Gly, Ala, Glu and Asp in mice single S180 cells were found to be in the range of 1.78–8.84, 0.95–2.31, 1.08–6.87, 1.03–4.05, 0.84–2.61 and 0.82–3.68 fmol, respectively. This work demonstrates that MCE coupled with CL detection is a useful analytical tool that is simple, quick and highly sensitive for single‐cell analysis.     

Simultaneous analysis of free amino acids and biogenic amines in honey and wine samples using in loop orthophthalaldeyde derivatization procedure

This work presents a RP-HPLC method for the simultaneous quantification of free amino acids and biogenic amines in liquid food matrices and the results of the application to honey and wine samples obtained from different production processes and geographic origins. The developed methodology is based on a pre-column derivatization with o-phthaldialdehyde carried out in the sample injection loop. The compounds were separated in a Nova-Pack RP-C(18) column (150 mm x 3.9 mm, 4 microm) at 35 degrees C. The mobile phase used was a mixture of phase A: 10 mM sodium phosphate buffer (pH 7.3), methanol and tetrahydrofuran (91:8:1); and phase B: methanol and phosphate buffer (80:20), with a flow rate of 1.0 ml/min. Fluorescence detection was used at an excitation wavelength of 335 nm and an emission wavelength of 440 nm. The separation and quantification of 19 amino acids and 6 amines was carried out in a single run as their OPA/MCE derivatives elute within 80 min, ensuring a reproducible quantification. The method showed to be adequate for the purpose, with an average RSD of 2% for the different amino acids; detection limits varying between 0.71 mg/l (Asn) and 8.26 mg/l (Lys) and recovery rates between 63.0% (Cad) and 98.0% (Asp). The amino acids present at the highest concentration in honey and wine samples were phenylalanine and arginine, respectively. Only residual levels of biogenic amines were detected in the analysed samples.     

Fluid dynamics of dilute suspensions and fouling of tubular membrane modules

The role of dilute suspensions in fouling a ultrafilter tubular membrane module is studied in detail for a wide range of wall permeation flux conditions. The inlet flow profiles are assumed to be either uniform (plug flow) or parabolic (fully developed) shape. It is assumed that the particles are neutrally buoyant and the concentrations are so low that it does not influence the fluid flow. Furthermore, the particle-particle interactions and the forces of interaction between the particle and the membrane wall are assumed to be unimportant. The governing equations of motion for the fluid are solved by a finite difference scheme. To compute the particulate fouling, the equations of motion for the particles are solved by the fourth-order Runge-Kutta-Gill method. Results are presented for both hydrodynamics and membrane fouling by dilute suspensions for conditions such as the effect of assumed inlet velocity profiles, and a wide range of wall permeation flux conditions.     

Chromatographic determination of sulfasalazine and its active metabolites: greenness assessment and application to spiked human plasma

Green TLC-densitometric and RP-HPLC methods were developed and validated for the determination of the active prodrug sulfasalazine (SZ), its active metabolite mesalazine (MZ) and the major active metabolite of mesalazine, N-acetyl-5-aminosalicylic acid (AS). In the developed TLC-densitometric method, chromatographic separation was carried out on TLC silica gel plates 60 F₂₅₄ using a developing system consisting of ethyl acetate–methanol–ammonia solution 33% (8:2.5:0.3, by volume) and then scanning the separated bands at 215 nm using hydrochlorothiazide as an internal standard with linearity ranges of 0.4–3, 0.4–2.4 and 0.3–2 for SZ, MZ and AS, respectively. The developed RP-HPLC method depended on chromatographic separation using a C₁₈ column with a solvent mixture of methanol–aqueous acetic acid solution (pH 5) as a mobile phase with gradient elution mode and UV scanning at 243 nm using pyrazinamide as internal standard with linearity ranges of 5–50, 5–40, and 3–20 for SZ, MZ and AS, respectively. US Food and Drug Administration guidelines were followed during validation of the methods. The greenness of the developed methods was estimated using the greenness profile and the Eco-Scale approach. Both methods passed the four quadrants of the greenness profile and had Eco-Scale score ˃75, thus they were considered to be green according to these approaches.     

Design of a portable gas chromatography with a conducting polymer nanocomposite detector device and a method to analyze a gas mixture

A portable chromatography device and a method were developed to analyze a gas mixture. The device comprises a chromatographic column for separating components of a sample of the gas mixture. It has an air pump coupled to the inlet of a chromatographic column for pumping air and an injector coupled to the inlet of chromatographic column for feeding the sample using the air as a carrier gas. A detector is arranged downstream from and coupled to the outlet of the chromatographic column. The detector is a nanostructure semiconductive microfiber. The device further comprises an evaluation unit arranged and configured to evaluate each detected component to determine the concentration. The designed portable system was used for simultaneous detection of amines. The possibility of applying dispersive liquid–liquid microextraction for the determination of analytes in trace levels is demonstrated. The reproducibility of this method is acceptable, and good standard deviations were obtained. The relative standard deviation value is less than 6% for all analytes. Finally, the method was successfully applied to the extraction and determination of analytes in water samples.