[Show abstract][Hide abstract] ABSTRACT: This paper reports a method to control the fluid flow in paper-based microfluidic devices simply by pressing over the channel surface of paper, thereby decreasing the pore size and permeability of a non-woven polypropylene sheet. As a result, fluid resistance is increased in the pressed region and causes flow rate to decrease. We characterize the decrease of flow rate with respect to different amounts of pressure applied, and up to 740% decrease in flow velocity was achieved. In addition, we demonstrate flow rate control in a Y-shaped merging paper and sequential delivery of multiple color dyes in a three-branched paper. Furthermore, sequential delivery of multiple fluid samples is performed to demonstrate its application in multi-step colorimetric immunoassay, which shows a 4.3-fold signal increase via enhancement step.
[Show abstract][Hide abstract] ABSTRACT: This paper demonstrates an inertia-activated cell sorting method to separate cells based on their surface protein expression by using inertial microfluidics. Target cells are immune-specifically reacted with antibody-coated microbeads and then separated from nontarget cells. As a proof of concept, separation of MCF-7 breast cancer cells from U937 lymphoma cells was achieved with 97.6% target cell recovery rate, 95% nontarget cell rejection ratio, 73.8% purity, and an enrichment ratio of 93 at a total flow rate of 8.75 mL/h without using any external forces.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report an efficient and high-performance immunoassay platform by combining high-density vertical ZnO nanowire array with photostable quantum dot (QD) labeling. The ZnO nanowire array provides a large surface area for the immobilization of biomolecules, which makes it an efficient substrate for the immunoreaction of biomolecules. When a sandwich immunoassay with QD label was conducted on various substrates, the ZnO nanowire substrate showed stronger fluorescence signal than ZnO thin film and bare glass substrates by 3.8 and 8.5 times, respectively. We found that the fluorescence resonance energy transfer (FRET) from QD to ZnO nanowire could be suppressed by extending their distance with multilayer biotin–streptavidin complex. In addition, we demonstrated the QD-based immunoassay of carcinoembryonic antigen (CEA) on a ZnO nanowire substrate, showing an excellent immunoassay performance with a very low detection limit (0.001 ng/mL) and a large detection range up to 100 ng/mL.
[Show abstract][Hide abstract] ABSTRACT: A microstructure-based hydrogel was employed to study the relationship between spatial specificity and cellular behavior, including cell fate, proliferation, morphology, and insulin secretion in pancreatic β-cells. To effectively form homogeneous cell clusters in vitro, we made cell-containing hydrogel membrane constructs with an adapted grid structure based on a hexagonal micropattern. Homogeneous cell clusters (average diameter: 83.6 ± 14.2 μm) of pancreatic insulinoma (MIN6) cells were spontaneously generated in the floating hydrogel membrane constructs, including a hexagonal grid structure (size of cavity: 100 μm, interval between cavities: 30 μm). Interestingly, 3D clustering of MIN6 cells mimicking the structure of pancreatic islets was coalesced into a merged aggregate attaching to each hexagonal cavity of the hydrogel grid structure. The fate and insulin secretion of homogeneous cell clusters in the hydrogel grid structure were also assessed. The results of these designable hydrogel-cell membrane constructs suggest that facultative in vitro β-cell proliferation and maintenance can be applied to biofunctional assessments.
[Show abstract][Hide abstract] ABSTRACT: Conventional molecular profiling methods using immunochemical assays have limits in terms of multiplexity and the quantification of biomarkers in investigation of cancer cells. In this paper, we demonstrate a quantum dot (QD)-based microfluidic multiple biomarker quantification (QD-MMBQ) method that enables labeling of more than eight proteins immunochemically on cell blocks within 1 h, in a quantitative manner. An internal reference, β-actin, was used as a loading control to compensate for differences in not only the cell number but also in staining quality among specimens. Furthermore, the microfluidic blocking method exhibited less nonspecific binding of QDs than the conventional static blocking method.
[Show abstract][Hide abstract] ABSTRACT: Loss of contractility and acquisition of an epithelial phenotype of vascular smooth muscle cells (VSMCs) are key events in proliferative vascular pathologies such as atherosclerosis and post-angioplastic restenosis. There is no proper cell culture system allowing differentiation of VSMCs so that it is difficult to delineate the molecular mechanism responsible for proliferative vasculopathy. We investigated whether a micropatterned substrate could restore the contractile phenotype of VSMCs in vitro. To induce and maintain the differentiated VSMC phenotype in vitro, we introduced a micropatterned groove substrate to modulate the morphology and function of VSMCs. Later than 7(th) passage of VSMCs showed typical synthetic phenotype characterized by epithelial morphology, increased proliferation rates and corresponding gene expression profiles; while short-term culture of these cells on a micropatterned groove induced a change to an intermediate phenotype characterized by low proliferation rates, increased migration, a spindle-like morphology associated with cytoskeletal rearrangement and expression of muscle-specific genes. Microarray analysis showed preferential expression of contractile and smooth muscle cell-specific genes in cells cultured on the micropatterned groove. Culture on a patterned groove may provide a valuable model for the study the role of VSMCs in normal vascular physiology and a variety of proliferative vascular diseases.
PLoS ONE 02/2014; 9(2):e88089. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes enhanced blood plasma separation by modulating the inertial lift force for separation in a contraction–expansion array (CEA) microchannel. By changing a contraction channel length, we observed the force modulation effects for size-based particle separation. In the CEA device, there are two force components that act in opposite direction to separate particles by size. By lengthening the contraction region in the CEA microchannel, we can easily control the lateral migration of desired particles by modulating a single force component (inertial lift force) without affecting the other (Dean drag force). From the experimental results, the inertial force ratio was calculated for prediction of force superiority between inertial lift force and Dean drag force, and applied to determine design parameters of the CEA microdevice for blood plasma separation. Using the force modulation in the microchannel, we successfully demonstrated enhancement of inertial blood plasma separation from human whole blood with a substantially high blood cell rejection ratio and a separation yield of 92.6% and 69.5%, respectively, with a throughput of 5.4 × 1011 cells/min.
Sensors and Actuators B Chemical 01/2014; 190:311-317. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dielectrophoresis (DEP) is an effective method to trap, manipulate and separate various dielectric particles. To generate a DEP force, a spatially nonuniform electrical field has been generated by an array of electrodes, while electrodeless DEP has been accomplished by placing an insulating material between two electrodes. Here, we describe a new DEP method for generating a nonuniform electrical field using a slanted microchannel. The electric field gradient is induced due to a slope in the channel and can be used to move and separate particles. Based on the gradual electric field induced by three dimensional structure of the microchannel, our method enables particles of different sizes to be separated solely by DEP force without flow. The slanted microchannel was easily fabricated by a replica molding technique using a commercial UV-cured photopolymer (NOA 63) and bonded as an insulating layer between two indium-tin-oxide films. By applying the electrical field, polystyrene beads of different sizes (6-45 microm in diameter) were trapped and separated depending on the applied electric strength and frequency. Using this method, the opportunistic pathogen Pseudomonas aeruginosa attached to antibody-conjugated microbeads was successfully separated from Escherichia coli in a slanted microchannel.
Journal of Nanoscience and Nanotechnology 12/2013; 13(12):7993-7. · 1.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microparticle adsorption on microchannel walls occurs frequently due to nonspecific interactions, decreasing operational performance in pressure-driven microfluidic systems. However, it is essential for delicate manipulation of microparticles or cells to maintain smooth fluid traffic. Here, we report a novel microparticle injection technique, which prevents particle loss, assisted by sample injection along the direction of fluid flow. Sample fluids, including microparticles, mammalian (U937) and green algae (Chlorella vulgaris) cells, were injected directly via a through-hole drilled in the lateral direction, resulting in a significant reduction in microparticle attachment. For digital microfluidic application, the proposed regime achieved a twofold enhancement of single-cell encapsulation compared to the conventional encapsulation rate, based on a Poisson distribution, by reducing the number of empty droplets. This novel interconnection method can be straightforwardly integrated as a microparticle or cell injection component in integrated microfluidic systems.
[Show abstract][Hide abstract] ABSTRACT: Microalgae, a group of microorganisms that grow using sunlight as the sole energy source and carbon dioxide as an only carbon source, have been considered as a feedstock of choice for the production of biofuels such as biodiesel. To explore the economic feasibility of such application, however, many technical hurdles must first be overcome; the selection and/or screening of competent species are some of the most important and yet challenging tasks. To greatly accelerate this rather slow and laborious step, we developed a droplet-based microfluidic system that uses alginate hydrogel microcapsules with a mean diameter of 26 μm, each of which is able to encapsulate a single microalgal cell. This novel device was successfully demonstrated using three microalgae species, namely, Chlorella vulgaris , Chlamydomonas sp., and Botryococcus braunii . In situ analysis of the lipid content of individual microalgal cells by nondestructive fluorescence staining using BODIPY (4,4-difluoro-1,3,5,7,-tetramethyl-4-bora-3a,4a-diaza-s-indacene) was possible. In all cases, we confirmed that the lipid content of microalgal species in alginate hydrogel microcapsules was comparable to that of free-living cells. Stochastic heterogeneity in the lipid content was verified under a highly viable physiological condition, implying that other analyses were possible after the determination of lipid content. Furthermore, the designed microwell arrays enabled us to distinguish the BODIPY fluorescence response of a single live alga within the microcapsules.
[Show abstract][Hide abstract] ABSTRACT: We present a simple method with the aid of a microfluidic droplet-generation technique to fabricate magnetic Janus particles by utilizing a solvent evaporation-induced phase separation and preferential partitioning of magnetic nanoparticles in the polymer blends. Non-aqueous emulsion droplets of the polymer blends and nanoparticles solution are produced to become Janus particles after the evaporation of the solvent. The stabilizing polymer of the nanoparticles, which is compatible only with one of the polymer blends to be phase-separated, plays a key role in the anisotropic positioning of the nanoparticles in the Janus particles. Using this phase separation-based method and microfluidics, excellent control over the size, size distribution, and morphology of the particles is achieved. Especially, we could control the morphology of the Janus particles easily by varying the volume ratio of the polymers. However, with an analysis of the shapes of resulting Janus particles, we found that non-equilibrium aspects of the evaporation-induced phase separation play a major role in determining the particle morphology. We expect that the versatility of this method in the choice of polymer blends and functional nanoparticles will enable the fabrication of colloids with various functionality and desired morphology.
[Show abstract][Hide abstract] ABSTRACT: We report a contraction-expansion array (CEA) microchannel device that performs label-free high throughput separation of cancer cells from whole blood at low Reynolds number (Re). The CEA microfluidic device utilizes hydrodynamic field effect for cancer cell separation, two kinds of inertial effects: (1) inertial lift force and (2) Dean flow, which results in label-free size-based separation with high throughput. To avoid cell damages potentially caused by high shear stress in conventional inertial separation techniques, the CEA microfluidic device isolates the cells with low operational Re, maintaining high-throughput separation using non-diluted whole blood sample (hematocrit ~45%). We characterized inertial particle migration and investigated the migration of blood cells and various cancer cells (MCF-7, SK-BR-3, and HCC70) in the CEA microchannel. The separation of cancer cells from whole blood was demonstrated with a cancer cell recovery rate of 99.1%, a blood cell rejection ratio of 88.9% and a throughput of 1.1 × 10(8) cells/min. In addition, the blood cell rejection ratio was further improved to 97.3% by two-step filtration process with two devices connected in series.
[Show abstract][Hide abstract] ABSTRACT: Behavior of metal–polymer hybrid colloidal particles in an optoelectrofluidic device has been investigated theoretically and experimentally. In the application of hundreds of kHz ac voltage, a variety of optically induced electrokinetic and electrostatic mechanisms affect the movement of gold-coated polystyrene microspheres. The particles repel from the light pattern, and their mobility increases as the amount of gold increases. We apply this model to develop an optoelectrofluidic immunoassay, in which the corresponding metal–polymer hybrid particles are formed by a reaction of antibody-coated gold nanoparticles, antigens, and antibody-coated polystyrene microspheres.
[Show abstract][Hide abstract] ABSTRACT: Nanobio versus Bionano - what's in a name? This special Issue of Biotechnology Journal includes two sections, one featuring articles on nanobio, the other articles on bionano. The editors of the issue, François Baneyx and Je-Kyun Park discuss the similarities and differencesbetween the two in their editorial.
[Show abstract][Hide abstract] ABSTRACT: Dielectrophoresis (DEP) is an effective method to trap, manipulate and separate various dielectric particles. To generate a DEP force, a spatially nonuniform electrical field has been generated by an array of electrodes, while electrodeless DEP has been accomplished by placing an insulating mate-rial between two electrodes. Here, we describe a new DEP method for generating a nonuniform electrical field using a slanted microchannel. The electric field gradient is induced due to a slope in the channel and can be used to move and separate particles. Based on the gradual electric field induced by three dimensional structure of the microchannel, our method enables particles of differ-ent sizes to be separated solely by DEP force without flow. The slanted microchannel was easily fabricated by a replica molding technique using a commercial UV-cured photopolymer (NOA 63) and bonded as an insulating layer between two indium-tin-oxide films. By applying the electrical field, polystyrene beads of different sizes (6–45 m in diameter) were trapped and separated depend-ing on the applied electric strength and frequency. Using this method, the opportunistic pathogen Pseudomonas aeruginosa attached to antibody-conjugated microbeads was successfully separated from Escherichia coli in a slanted microchannel.
Journal of Nanoscience and Nanotechnology 01/2013; 13(12):7993. · 1.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper introduces a novel immunohistochemical method for accurate quantification of multiple biomarkers on cancer tissues using a microfluidic multiplexed immunostaining system. Due to heterogeneity in cancer tissues, a conventional multi-channel based biomarker multiplexing strategy can cause missing of some biomarker expressions. However, our tumor-specific antigenic site selection strategy ensures obtaining of all biomarker signals, which are correctly attained from every microchannel regardless of tissue heterogeneity. Moreover, the microfluidics-aided blocking process shows superior blocking performance over the static blocking process and precise controllability by adjusting the flow rate.
Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII: The 17th International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: A quantitative, reproducible, fast and inexpensive multiplexed immunohistochemistry (IHC) system might play a locomotive role in drug screening and personalized medicine. Currently, fully automated IHC machines and sequential multiplexed IHC methods based upon multiple color reagents have been developed, with the evolution of such methods having revealed novel biological findings over the conventional IHC method, which is time consuming and labor intensive. We describe a novel parallel multiplexed IHC method using a microfluidic multiplexed immunohistochemistry (MMIHC) device for quantitative pathological diagnosis of breast cancer. The key factors for success of parallel multiplexed IHC are the fabrication of a robust microfluidic device, the interface between the device and a tissue slide, and an accurate fluidic control for multiple IHC reagents. In order to apply conventional thin-section tissues into on-chip systems without any additional modification process, a tissue slide-compatible assembler was developed for optimal compatibility of conventional IHC methods. With this approach, a perfect fluid control for various solutions was demonstrated without any leakage, bubble formation or cross-contamination. The results presented in this chapter indicate that the microfluidic IHC protocol developed can provide the possibility of tailored cancer treatments as well as precise histopathological diagnosis using numerous specific biomarkers.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we proposed a novel and efficient quantum dot (QD)-based immunoassay method on the zinc oxide (ZnO) nanowire substrate. The ZnO nanowire substrate increases the immobilization sites for biomolecules, which results in the enhancement of fluorescence signal in QD-labeled immunoassay. However, energy transfer happens between the ZnO nanowire and QDs when QD is introduced as a labeling material. To prevent this energy transfer, we applied biotin-streptavidin complex to prolong the distance between two nanomaterials. Triple layers of biotin-streptavidin complexes reduced the energy transfer successfully. This immunoassay system was applied to quantify the concentration of carcinoembryonic antigen (CEA).
Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII: The 17th International Conference on; 01/2013