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Xu D, Zhang W, Li H, Li N, Lin JM. Advances in droplet digital polymerase chain reaction on microfluidic chips. LAB ON A CHIP 2023; 23:1258-1278. [PMID: 36752545 DOI: 10.1039/d2lc00814a] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The PCR technique has been known to the general public since the pandemic outbreak of COVID-19. This technique has progressed through three stages: from simple PCR to real-time fluorescence PCR to digital PCR. Among them, the microfluidic-based droplet digital PCR technique has attracted much attention and has been widely applied due to its advantages of high throughput, high sensitivity, low reagent consumption, low cross-contamination, and absolute quantification ability. In this review, we introduce various designs of microfluidic-based ddPCR developed within the last decade. The microfluidic-based droplet generation methods, thermal cycle strategies, and signal counting approaches are described, and the applications in the fields of single-cell analysis, disease diagnosis, and pathogen detection are introduced. Further, the challenges and prospects of microfluidic-based ddPCR are discussed. We hope that this review can contribute to the further development of the microfluidic-based ddPCR technique.
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Affiliation(s)
- Danfeng Xu
- Key Laboratory of Chemical Metrology and Applications on Nutrition and Health for State Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China.
| | - Weifei Zhang
- Key Laboratory of Chemical Metrology and Applications on Nutrition and Health for State Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China.
| | - Hongmei Li
- Key Laboratory of Chemical Metrology and Applications on Nutrition and Health for State Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China.
| | - Nan Li
- Department of Chemistry, Beijing Key Laboratory of Microanalytical Methods and Instrumentation Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), China.
| | - Jin-Ming Lin
- Department of Chemistry, Beijing Key Laboratory of Microanalytical Methods and Instrumentation Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), China.
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2
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Yue X, Fang X, Sun T, Yi J, Kuang X, Guo Q, Wang Y, Gu H, Xu H. Breaking through the Poisson Distribution: A compact high-efficiency droplet microfluidic system for single-bead encapsulation and digital immunoassay detection. Biosens Bioelectron 2022; 211:114384. [DOI: 10.1016/j.bios.2022.114384] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 04/25/2022] [Accepted: 05/14/2022] [Indexed: 11/02/2022]
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3
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Quantitative electrolysis of droplet contents in microfluidic channels. Concept and experimental validation. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.139017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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4
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Shi N, Mohibullah M, Easley CJ. Active Flow Control and Dynamic Analysis in Droplet Microfluidics. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2021; 14:133-153. [PMID: 33979546 PMCID: PMC8956363 DOI: 10.1146/annurev-anchem-122120-042627] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Droplet-based microfluidics has emerged as an important subfield within the microfluidic and general analytical communities. Indeed, several unique applications such as digital assay readout and single-cell sequencing now have commercial systems based on droplet microfluidics. Yet there remains room for this research area to grow. To date, most analytical readouts are optical in nature, relatively few studies have integrated sample preparation, and passive means for droplet formation and manipulation have dominated the field. Analytical scientists continue to expand capabilities by developing droplet-compatible method adaptations, for example, by interfacing to mass spectrometers or automating droplet sampling for temporally resolved analysis. In this review, we highlight recently developed fluidic control techniques and unique integrations of analytical methodology with droplet microfluidics-focusing on automation and the connections to analog/digital domains-and we conclude by offering a perspective on current challenges and future applications.
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Affiliation(s)
- Nan Shi
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, USA;
| | - Md Mohibullah
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, USA;
| | - Christopher J Easley
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, USA;
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5
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Kang KK, Lee B, Lee CS. Recent progress in the synthesis of inorganic particulate materials using microfluidics. J Taiwan Inst Chem Eng 2019. [DOI: 10.1016/j.jtice.2018.08.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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6
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Alkayyali T, Cameron T, Haltli B, Kerr R, Ahmadi A. Microfluidic and cross-linking methods for encapsulation of living cells and bacteria - A review. Anal Chim Acta 2019; 1053:1-21. [DOI: 10.1016/j.aca.2018.12.056] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Revised: 12/24/2018] [Accepted: 12/26/2018] [Indexed: 12/14/2022]
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7
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Abstract
Droplet microfluidics generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels. Due to its remarkable advantages, droplet microfluidics bears significant value in an extremely wide range of area. In this review, we provide a comprehensive and in-depth insight into droplet microfluidics, covering fundamental research from microfluidic chip fabrication and droplet generation to the applications of droplets in bio(chemical) analysis and materials generation. The purpose of this review is to convey the fundamentals of droplet microfluidics, a critical analysis on its current status and challenges, and opinions on its future development. We believe this review will promote communications among biology, chemistry, physics, and materials science.
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Affiliation(s)
- Luoran Shang
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China
| | - Yao Cheng
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China
| | - Yuanjin Zhao
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China
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8
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Luo R, Dinh ND, Chen CH. Fast-responsive hydrogel as an injectable pump for rapid on-demand fluidic flow control. BIOMICROFLUIDICS 2017; 11:034107. [PMID: 28798856 PMCID: PMC5533479 DOI: 10.1063/1.4983493] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 05/02/2017] [Indexed: 05/02/2023]
Abstract
Chemically synthesized functional hydrogels have been recognized as optimized soft pumps for on-demand fluidic regulation in micro-systems. However, the challenges regarding the slow responses of hydrogels have very much limited their application in effective fluidic flow control. In this study, a heterobifunctional crosslinker (4-hydroxybutyl acrylate)-enabled two-step hydrothermal phase separation process for preparing a highly porous hydrogel with fast response dynamics was investigated for the fabrication of novel microfluidic functional units, such as injectable valves and pumps. The cylinder-shaped hydrogel, with a diameter of 9 cm and a height of 2.5 cm at 25 °C, achieved a size reduction of approximately 70% in less than 30 s after the hydrogels were heated at 40 °C. By incorporating polypyrrole nanoparticles as photothermal transducers, a photo-responsive composite hydrogel was approached and exhibited a remotely triggerable fluidic regulation and pumping ability to generate significant flows, showing on-demand water-in-oil droplet generation by laser switching, whereby the droplet size could be tuned by adjusting the laser intensity and irradiation period with programmable manipulation.
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Affiliation(s)
- Rongcong Luo
- Department of Biomedical Engineering, National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077
| | - Ngoc-Duy Dinh
- Department of Biomedical Engineering, National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077
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9
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Doonan SR, Bailey RC. K-Channel: A Multifunctional Architecture for Dynamically Reconfigurable Sample Processing in Droplet Microfluidics. Anal Chem 2017; 89:4091-4099. [PMID: 28222260 PMCID: PMC5812353 DOI: 10.1021/acs.analchem.6b05041] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
By rapidly creating libraries of thousands of unique, miniaturized reactors, droplet microfluidics provides a powerful method for automating high-throughput chemical analysis. In order to engineer in-droplet assays, microfluidic devices must add reagents into droplets, remove fluid from droplets, and perform other necessary operations, each typically provided by a unique, specialized geometry. Unfortunately, modifying device performance or changing operations usually requires re-engineering the device among these specialized geometries, a time-consuming and costly process when optimizing in-droplet assays. To address this challenge in implementing droplet chemistry, we have developed the "K-channel," which couples a cross-channel flow to the segmented droplet flow to enable a range of operations on passing droplets. K-channels perform reagent injection (0-100% of droplet volume), fluid extraction (0-50% of droplet volume), and droplet splitting (1:1-1:5 daughter droplet ratio). Instead of modifying device dimensions or channel configuration, adjusting external conditions, such as applied pressure and electric field, selects the K-channel process and tunes its magnitude. Finally, interfacing a device-embedded magnet allows selective capture of 96% of droplet-encapsulated superparamagnetic beads during 1:1 droplet splitting events at ∼400 Hz. Addition of a second K-channel for injection (after the droplet splitting K-channel) enables integrated washing of magnetic beads within rapidly moving droplets. Ultimately, the K-channel provides an exciting opportunity to perform many useful droplet operations across a range of magnitudes without requiring architectural modifications. Therefore, we envision the K-channel as a versatile, easy to use microfluidic component enabling diverse, in-droplet (bio)chemical manipulations.
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Affiliation(s)
- Steven R. Doonan
- Department of Chemistry, University of Illinois at Urbana Champaign, Urbana, Illinois, 61801, USA
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
| | - Ryan C. Bailey
- Department of Chemistry, University of Illinois at Urbana Champaign, Urbana, Illinois, 61801, USA
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
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10
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Zhu P, Wang L. Passive and active droplet generation with microfluidics: a review. LAB ON A CHIP 2016; 17:34-75. [PMID: 27841886 DOI: 10.1039/c6lc01018k] [Citation(s) in RCA: 495] [Impact Index Per Article: 61.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Precise and effective control of droplet generation is critical for applications of droplet microfluidics ranging from materials synthesis to lab-on-a-chip systems. Methods for droplet generation can be either passive or active, where the former generates droplets without external actuation, and the latter makes use of additional energy input in promoting interfacial instabilities for droplet generation. A unified physical understanding of both passive and active droplet generation is beneficial for effectively developing new techniques meeting various demands arising from applications. Our review of passive approaches focuses on the characteristics and mechanisms of breakup modes of droplet generation occurring in microfluidic cross-flow, co-flow, flow-focusing, and step emulsification configurations. The review of active approaches covers the state-of-the-art techniques employing either external forces from electrical, magnetic and centrifugal fields or methods of modifying intrinsic properties of flows or fluids such as velocity, viscosity, interfacial tension, channel wettability, and fluid density, with a focus on their implementations and actuation mechanisms. Also included in this review is the contrast among different approaches of either passive or active nature.
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Affiliation(s)
- Pingan Zhu
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China. and HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), 311300, Hangzhou, Zhejiang, China
| | - Liqiu Wang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China. and HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), 311300, Hangzhou, Zhejiang, China
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11
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12
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Chen YC, Liu K, Shen CKF, van Dam RM. On-demand generation and mixing of liquid-in-gas slugs with digitally-programmable composition and size. JOURNAL OF MICROMECHANICS AND MICROENGINEERING : STRUCTURES, DEVICES, AND SYSTEMS 2015; 25:084006. [PMID: 29167603 PMCID: PMC5695874 DOI: 10.1088/0960-1317/25/8/084006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Microscopic droplets or slugs of mixed reagents provide a convenient platform for performing large numbers of isolated biochemical or chemical reactions for many screening and optimization applications. Myriad microfluidic approaches have emerged for creating droplets or slugs with controllable size and composition, generally using an immiscible carrier fluid to assist with the formation or merging processes. We report a novel device for generation of liquid slugs in air when the use of a carrier liquid is not compatible with the application. The slug generator contains two adjacent chambers, each of which has a volume that can be digitally adjusted by closing selected microvalves. Reagents are filled into the two chambers, merged together into a contiguous liquid slug, ejected at the desired time from the device using gas pressure, and mixed by flowing in a downstream channel. Programmable size and composition of slugs is achieved by dynamically adjusting the volume of each chamber prior to filling. Slug formation in this fashion is independent of fluid properties and can easily be scaled to mix larger numbers of reagents. This device has already been used to screen monomer ratios in supramolecular nanoparticle assembly and radiolabeling conditions of engineered antibodies, and here we provide a detailed description of the underlying device.
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Affiliation(s)
| | | | - Clifton Kwang-Fu Shen
- Department of Molecular & Medical Pharmacology and Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, 570 Westwood Plaza, Los Angeles, CA 90095
| | - R. Michael van Dam
- Department of Molecular & Medical Pharmacology and Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, 570 Westwood Plaza, Los Angeles, CA 90095
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13
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Ding Y, Casadevall i Solvas X, deMello A. “V-junction”: a novel structure for high-speed generation of bespoke droplet flows. Analyst 2015; 140:414-21. [DOI: 10.1039/c4an01730g] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present the use of microfluidic “V-junctions” as a droplet generation strategy that incorporates enhanced performance characteristics when compared to more traditional “T-junction” formats.
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Affiliation(s)
- Yun Ding
- Department of Chemistry and Applied Biosciences
- Institute for Chemical and Bioengineering
- ETH Zurich
- Zurich
- Switzerland
| | - Xavier Casadevall i Solvas
- Department of Chemistry and Applied Biosciences
- Institute for Chemical and Bioengineering
- ETH Zurich
- Zurich
- Switzerland
| | - Andrew deMello
- Department of Chemistry and Applied Biosciences
- Institute for Chemical and Bioengineering
- ETH Zurich
- Zurich
- Switzerland
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14
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Tangen U, Sharma A, Wagler P, McCaskill JS. On demand nanoliter-scale microfluidic droplet generation, injection, and mixing using a passive microfluidic device. BIOMICROFLUIDICS 2015; 9:014119. [PMID: 25759752 PMCID: PMC4327917 DOI: 10.1063/1.4907895] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 01/29/2015] [Indexed: 05/10/2023]
Abstract
We here present and characterize a programmable nanoliter scale droplet-on-demand device that can be used separately or readily integrated into low cost single layer rapid prototyping microfluidic systems for a wide range of user applications. The passive microfluidic device allows external (off-the-shelf) electronically controlled pinch valves to program the delivery of nanoliter scale aqueous droplets from up to 9 different inputs to a central outlet channel. The inputs can be either continuous aqueous fluid streams or microliter scale aqueous plugs embedded in a carrier fluid, in which case the number of effective input solutions that can be employed in an experiment is no longer strongly constrained (100 s-1000 s). Both nanoliter droplet sequencing output and nanoliter-scale droplet mixing are reported with this device. Optimization of the geometry and pressure relationships in the device was achieved in several hardware iterations with the support of open source microfluidic simulation software and equivalent circuit models. The requisite modular control of pressure relationships within the device is accomplished using hydrodynamic barriers and matched resistance channels with three different channel heights, custom parallel reversible microfluidic I/O connections, low dead-volume pinch valves, and a simply adjustable array of external screw valves. Programmable sequences of droplet mixes or chains of droplets can be achieved with the device at low Hz frequencies, limited by device elasticity, and could be further enhanced by valve integration. The chip has already found use in the characterization of droplet bunching during export and the synthesis of a DNA library.
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Affiliation(s)
- Uwe Tangen
- Faculty of Chemistry and Biochemistry, Microsystems Chemistry and BioIT (BioMIP), Ruhr-University Bochum , 44780 Bochum, Germany
| | - Abhishek Sharma
- Faculty of Chemistry and Biochemistry, Microsystems Chemistry and BioIT (BioMIP), Ruhr-University Bochum , 44780 Bochum, Germany
| | - Patrick Wagler
- Faculty of Chemistry and Biochemistry, Microsystems Chemistry and BioIT (BioMIP), Ruhr-University Bochum , 44780 Bochum, Germany
| | - John S McCaskill
- Faculty of Chemistry and Biochemistry, Microsystems Chemistry and BioIT (BioMIP), Ruhr-University Bochum , 44780 Bochum, Germany
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15
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Zeng Y, Shin M, Wang T. Programmable active droplet generation enabled by integrated pneumatic micropumps. LAB ON A CHIP 2013; 13:267-73. [PMID: 23160148 DOI: 10.1039/c2lc40906b] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
In this work we have investigated the integrated diaphragm micropump as an active fluidic control approach for the on-demand generation of droplets with precisely defined size, frequency and timing. In contrast to valve-actuated devices that only modulate the flow of the dispersed phase being continuously injected, this integrated micropump allows the combination of fluidic transport and modulation to achieve active control of droplet generation. A distinct characteristic of this method compared to the valve modulated droplet formation processes is that it enables independent control of droplet generation frequency by adjusting the pumping frequency and droplet size by flow conditions. We also demonstrated the generation of complex droplet patterns through programming the pumping configurations and the application to multi-volume digital PCR for precise and quantitative detection of genetic targets. Overall, our results suggest that the pump-based droplet microfluidics provide a robust platform for programmable active droplet generation which could facilitate the development of high-performance chemical and biological assays.
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Affiliation(s)
- Yong Zeng
- Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA.
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16
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Kemna EWM, Segerink LI, Wolbers F, Vermes I, van den Berg A. Label-free, high-throughput, electrical detection of cells in droplets. Analyst 2013; 138:4585-92. [DOI: 10.1039/c3an00569k] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Lin R, Fisher JS, Simon MG, Lee AP. Novel on-demand droplet generation for selective fluid sample extraction. BIOMICROFLUIDICS 2012; 6:24103-2410310. [PMID: 22655015 PMCID: PMC3360719 DOI: 10.1063/1.3699972] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 03/05/2012] [Indexed: 05/11/2023]
Abstract
A novel microfluidic device enabling selective generation of droplets and encapsulation of targets is presented. Unlike conventional methods, the presented mechanism generates droplets with unique selectivity by utilizing a K-junction design. The K-junction is a modified version of the classic T-junction with an added leg that serves as the exit channel for waste. The dispersed phase fluid enters from one diagonal of the K and exits the other diagonal while the continuous phase travels in the straight leg of the K. The intersection forms an interface that allows the dispersed phase to be controllably injected through actuation of an elastomer membrane located above the inlet channel near the interface. We have characterized two critical components in controlling the droplet size-membrane actuation pressure and timing as well as identified the region of fluid in which the droplet will be formed. This scheme will have applications in fluid sampling processes and selective encapsulation of materials. Selective encapsulation of a single cell from the dispersed phase fluid is demonstrated as an example of functionality of this design.
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Affiliation(s)
- Robert Lin
- University of California-Irvine, Irvine, California 92697, USA
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