Special Issue "Droplet Microfluidics: Techniques and Technologies"

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (31 July 2015).

Special Issue Editors

Prof. Andrew J. deMello
E-Mail Website
Guest Editor
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zurich, Switzerland
Interests: segmented flows; optical spectroscopies; nanoparticle synthesis; diagnostics, exosomes
Special Issues and Collections in MDPI journals
Dr. Xavier Casadevall i Solvas
E-Mail Website
Guest Editor
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
Tel. +41 44 633 04 20
Interests: droplet microfluidics; small organism assays
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Droplet-based microfluidic platforms are increasingly used in a wide variety of situations in the chemical and biological sciences. For example, genetic and transcriptomic screens, nanomaterial synthesis, single cell assays, proteomics, and clinical diagnostics have all profited from the adoption of such formats. Key advantages associated with droplet-based microfluidics include the reduced consumption of reagents, the ability to handle target molecules at a low copy number with exceptionally high analytical throughput (droplets are typically generated at kHz frequencies). To realize their full potential, there is a recognized need to develop, refine, and integrate basic unit operations for the manipulation and processing of pL-volume droplets. Regardless, in recent years, it has become progressively more difficult to disseminate pure engineering developments of this kind. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments for the generation, manipulation, and utilization of droplets in a variety of formats, with particular interest being paid to techniques for large scale/high content screens, high-throughput experimentation, and single droplet identification/manipulation.

Prof. Dr. Andrew deMello
Dr. Xavier Casadevall i Solvas
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.


Keywords

  • microdroplet operations
  • microfluidic techniques
  • high throughput screening
  • large-scale assays
  • high content screens
  • lab on a chip
  • micro total analysis systems

Published Papers (18 papers)

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Research

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Open AccessArticle
Generation of Oil Droplets in a Non-Newtonian Liquid Using a Microfluidic T-Junction
Micromachines 2015, 6(12), 1825-1835; https://doi.org/10.3390/mi6121458 - 30 Nov 2015
Cited by 16
Abstract
We have compared the formation of oil drops in Newtonian and non-Newtonian fluids in a T-junction microfluidic device. As Newtonian fluids, we used aqueous solutions of glycerol, while as non-Newtonian fluids we prepared aqueous solutions of xanthan, a stiff rod-like polysaccharide, which exhibit [...] Read more.
We have compared the formation of oil drops in Newtonian and non-Newtonian fluids in a T-junction microfluidic device. As Newtonian fluids, we used aqueous solutions of glycerol, while as non-Newtonian fluids we prepared aqueous solutions of xanthan, a stiff rod-like polysaccharide, which exhibit strong shear-thinning effects. In the squeezing regime, the formation of oil droplets in glycerol solutions is found to scale with the ratio of the dispersed flow rate to the continuous one and with the capillary number associated to the continuous phase. Switching to xanthan solutions does not seem to significantly alter the droplet formation process. Any quantitative difference with respect to the Newtonian liquid can be accounted for by a suitable choice of the capillary number, corresponding to an effective xanthan viscosity that depends on the flow rates. We have deduced ample variations in the viscosity, on the order of 10 and more, during normal operation conditions of the T-junction. This allowed estimating the actual shear rates experienced by the xanthan solutions, which go from tens to hundreds of s−1. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Digital Microfluidic System with Vertical Functionality
Micromachines 2015, 6(11), 1655-1674; https://doi.org/10.3390/mi6111448 - 04 Nov 2015
Cited by 4
Abstract
Digital (droplet) microfluidics (DµF) is a powerful platform for automated lab-on-a-chip procedures, ranging from quantitative bioassays such as RT-qPCR to complete mammalian cell culturing. The simple MEMS processing protocols typically employed to fabricate DµF devices limit their functionality to two dimensions, and hence [...] Read more.
Digital (droplet) microfluidics (DµF) is a powerful platform for automated lab-on-a-chip procedures, ranging from quantitative bioassays such as RT-qPCR to complete mammalian cell culturing. The simple MEMS processing protocols typically employed to fabricate DµF devices limit their functionality to two dimensions, and hence constrain the applications for which these devices can be used. This paper describes the integration of vertical functionality into a DµF platform by stacking two planar digital microfluidic devices, altering the electrode fabrication process, and incorporating channels for reversibly translating droplets between layers. Vertical droplet movement was modeled to advance the device design, and three applications that were previously unachievable using a conventional format are demonstrated: (1) solutions of calcium dichloride and sodium alginate were vertically mixed to produce a hydrogel with a radially symmetric gradient in crosslink density; (2) a calcium alginate hydrogel was formed within the through-well to create a particle sieve for filtering suspensions passed from one layer to the next; and (3) a cell spheroid formed using an on-chip hanging-drop was retrieved for use in downstream processing. The general capability of vertically delivering droplets between multiple stacked levels represents a processing innovation that increases DµF functionality and has many potential applications. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
A Double Emulsion-Based, Plastic-Glass Hybrid Microfluidic Platform for Protein Crystallization
Micromachines 2015, 6(11), 1629-1644; https://doi.org/10.3390/mi6111446 - 28 Oct 2015
Cited by 3
Abstract
This paper reports the design and construction of a plastic-glass hybrid microfluidic platform for performing protein crystallization trials in nanoliter double emulsions. The double emulsion-based protein crystallization trials were implemented with both the vapor-diffusion method and microbatch method by controlling the diffusion of [...] Read more.
This paper reports the design and construction of a plastic-glass hybrid microfluidic platform for performing protein crystallization trials in nanoliter double emulsions. The double emulsion-based protein crystallization trials were implemented with both the vapor-diffusion method and microbatch method by controlling the diffusion of water between the inner and outer phases and by eliminating water evaporation. Double emulsions, whose inner and outer environments can be easily adjusted, can provide ideal conditions to explore protein crystallization with the advantages of a convection-free environment and a homogeneous interface. The property of the water-oil interface was demonstrated to be a critical factor for nucleation, and appropriate surfactants should be chosen to prevent protein adsorption at the interface. The results from the volume effect study showed a trend of fewer crystals and longer incubation time when the protein solution volume became smaller, suggesting that the nucleation in protein crystallization process can be controlled by changing the volume of protein solutions. Finally, sparse matrix screening was achieved using the double emulsion-based microbatch method. The double emulsion-based approach for protein crystallization is a promising tool for enhancing the crystal quality by controlling the nucleation process. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Droplet Microfluidic Technique for the Study of Fermentation
Micromachines 2015, 6(10), 1514-1525; https://doi.org/10.3390/mi6101435 - 07 Oct 2015
Cited by 5
Abstract
We demonstrate a technique that uses microdroplets for culturing and selecting bacterial cultures in a model biotechnological application. We propose an assay for determination of ethanol concentration that provides increased dynamic range and is compatible with droplet microfluidic screening technologies. The assay comprises [...] Read more.
We demonstrate a technique that uses microdroplets for culturing and selecting bacterial cultures in a model biotechnological application. We propose an assay for determination of ethanol concentration that provides increased dynamic range and is compatible with droplet microfluidic screening technologies. The assay comprises two enzymes—alcohol oxidase (AOX) and horseradish peroxidase (HRP)—and a colorimetric readout system of phenol-4-sulfonic acid (PSA) and 4-aminoantipyrine (4-AAP). The microdroplet method provides high repeatability (a relative error of measured ethanol concentration < 5%), high specificity for ethanol, low consumption of reagents and wide dynamic range (1–70 g·L-1) compared to existing assays. We report the use of this method in a screen of ethanol generation efficiency of Zymomonas mobilis (strain 3881) against the concentration of glucose in the culture media. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Refined Method for Droplet Microfluidics-Enabled Detection of Plasmodium falciparum Encoded Topoisomerase I in Blood from Malaria Patients
Micromachines 2015, 6(10), 1505-1513; https://doi.org/10.3390/mi6101432 - 05 Oct 2015
Cited by 4
Abstract
Rapid and reliable diagnosis is essential in the fight against malaria, which remains one of the most deadly infectious diseases in the world. In the present study we take advantage of a droplet microfluidics platform combined with a novel and user-friendly biosensor for [...] Read more.
Rapid and reliable diagnosis is essential in the fight against malaria, which remains one of the most deadly infectious diseases in the world. In the present study we take advantage of a droplet microfluidics platform combined with a novel and user-friendly biosensor for revealing the main malaria-causing agent, the Plasmodium falciparum (P. falciparum) parasite. Detection of the parasite is achieved through detection of the activity of a parasite-produced DNA-modifying enzyme, topoisomerase I (pfTopoI), in the blood from malaria patients. The assay presented has three steps: (1) droplet microfluidics-enabled extraction of active pfTopoI from a patient blood sample; (2) pfTopoI-mediated modification of a specialized DNA biosensor; (3) readout. The setup is quantitative and specific for the detection of Plasmodium topoisomerase I. The procedure is a considerable improvement of the previously published Rolling Circle Enhanced Enzyme Activity Detection (REEAD) due to the advantages of involving no signal amplification steps combined with a user-friendly readout. In combination these alterations represent an important step towards exploiting enzyme activity detection in point-of-care diagnostics of malaria. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Enhancing Throughput of Combinatorial Droplet Devices via Droplet Bifurcation, Parallelized Droplet Fusion, and Parallelized Detection
Micromachines 2015, 6(10), 1490-1504; https://doi.org/10.3390/mi6101434 - 05 Oct 2015
Cited by 4
Abstract
Combinatorial droplet microfluidic devices with programmable microfluidic valves have recently emerged as a viable approach for performing multiplexed experiments in microfluidic droplets. However, the serial operation in these devices restricts their throughput. To address this limitation, we present a parallelized combinatorial droplet device [...] Read more.
Combinatorial droplet microfluidic devices with programmable microfluidic valves have recently emerged as a viable approach for performing multiplexed experiments in microfluidic droplets. However, the serial operation in these devices restricts their throughput. To address this limitation, we present a parallelized combinatorial droplet device that enhances device throughput via droplet bifurcation, parallelized droplet fusion, and parallelized droplet detection. In this device, sample droplets split evenly at bifurcating Y-junctions before multiple independent reagent droplets are injected directly into the split sample droplets for robust droplet fusion. Finally, the fused sample and reagent droplets can be imaged in parallel via microscopy. The combination of these approaches enabled us to improve the throughput over traditional, serially-operated combinatorial droplet devices by 16-fold—with ready potential for further enhancement. Given its current performance and prospect for future improvements, we believe the parallelized combinatorial droplet device has the potential to meet the demand as a flexible and cost-effective tool that can perform high throughput screening applications. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Floating Droplet Array: An Ultrahigh-Throughput Device for Droplet Trapping, Real-time Analysisand Recovery
Micromachines 2015, 6(10), 1469-1482; https://doi.org/10.3390/mi6101431 - 30 Sep 2015
Cited by 10
Abstract
We describe the design, fabrication and use of a dual-layered microfluidic device for ultrahigh-throughput droplet trapping, analysis, and recovery using droplet buoyancy. To demonstrate the utility of this device for digital quantification of analytes, we quantify the number of droplets, which contain a [...] Read more.
We describe the design, fabrication and use of a dual-layered microfluidic device for ultrahigh-throughput droplet trapping, analysis, and recovery using droplet buoyancy. To demonstrate the utility of this device for digital quantification of analytes, we quantify the number of droplets, which contain a β-galactosidase-conjugated bead among more than 100,000 immobilized droplets. In addition, we demonstrate that this device can be used for droplet clustering and real-time analysis by clustering several droplets together into microwells and monitoring diffusion of fluorescein, a product of the enzymatic reaction of β-galactosidase and its fluorogenic substrate FDG, between droplets. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Shielding Electric Fields to Prevent Coalescence of Emulsions in Microfluidic Channels Using a 3D Metallic Coil
Micromachines 2015, 6(10), 1459-1468; https://doi.org/10.3390/mi6101430 - 30 Sep 2015
Abstract
In microfluidics, electric fields are widely used to assist the generation and the manipulation of droplets or jets. However, uncontrolled electric field can disrupt the operation of an integrated microfluidic system, for instance, through undesired coalescence of droplets, undesired changes in the wettability [...] Read more.
In microfluidics, electric fields are widely used to assist the generation and the manipulation of droplets or jets. However, uncontrolled electric field can disrupt the operation of an integrated microfluidic system, for instance, through undesired coalescence of droplets, undesired changes in the wettability of the channel wall or unexpected death of cells. Therefore, an approach to control the distribution of electric fields inside microfluidic channels is needed. Inspired by the electro-magnetic shielding effect in electrical and radiation systems, we demonstrate the shielding of electric fields by incorporating 3D metallic coils in microfluidic devices. Using the degree of coalescence of emulsion drops as an indicator, we have shown that electric fields decrease dramatically in micro-channels surrounded by these conductive metallic coils both experimentally and numerically. Our work illustrates an approach to distribute electric fields in integrated microfluidic networks by selectively installing metallic coils or electrodes, and represents a significant step towards large-scale electro-microfluidic systems. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Hydrophilic Surface Modification of PDMS Microchannel for O/W and W/O/W Emulsions
Micromachines 2015, 6(10), 1445-1458; https://doi.org/10.3390/mi6101429 - 29 Sep 2015
Cited by 12
Abstract
A surface modification method for bonded polydimethylsiloxane (PDMS) microchannels is presented herein. Polymerization of acrylic acid was performed on the surface of a microchannel using an inline atmospheric pressure dielectric barrier microplasma technique. The surface treatment changes the wettability of the microchannel from [...] Read more.
A surface modification method for bonded polydimethylsiloxane (PDMS) microchannels is presented herein. Polymerization of acrylic acid was performed on the surface of a microchannel using an inline atmospheric pressure dielectric barrier microplasma technique. The surface treatment changes the wettability of the microchannel from hydrophobic to hydrophilic. This is a challenging task due to the fast hydrophobic recovery of the PDMS surface after modification. This modification allows the formation of highly monodisperse oil-in-water (O/W) droplets. The generation of water-in-oil-in-water (W/O/W) double emulsions was successfully achieved by connecting in series a hydrophobic microchip with a modified hydrophilic microchip. An original channel blocking technique to pattern the surface wettability of a specific section of a microchip using a viscous liquid comprising a mixture of honey and glycerol, is also presented for generating W/O/W emulsions on a single chip. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Biconvex Polymer Microlenses with Tunable Imaging Properties Designed by Janus Droplet Microfluidics
Micromachines 2015, 6(10), 1435-1444; https://doi.org/10.3390/mi6101428 - 29 Sep 2015
Cited by 8
Abstract
This work presents a technique for fabricating biconvex polymer microlenses using microfluidics, and then evaluates their tunable optical properties. A glass microfluidic channel was employed to rapidly mass-produce nanoliter-sized biphasic Janus droplets, which consist of a biconvex segment of a photocurable monomer and [...] Read more.
This work presents a technique for fabricating biconvex polymer microlenses using microfluidics, and then evaluates their tunable optical properties. A glass microfluidic channel was employed to rapidly mass-produce nanoliter-sized biphasic Janus droplets, which consist of a biconvex segment of a photocurable monomer and a concave-convex segment of a non-curable silicone oil that contained a surfactant. Subsequent photopolymerization produces polymeric biconvex spherical microlenses with templated dual curvatures. By changing the flow-rate ratios of the photocurable and non-curable droplet phases in the microfluidic channel, the radii of curvature of the two lens surfaces and the thicknesses of the resultant microlenses can be varied. The resulting biconvex microlenses with different shapes were used in image projection experiments. Different magnification properties were observed, and were consistent with the properties estimated quantitatively from the geometrical parameters of the lenses. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Microfluidic Induced Controllable Microdroplets Assembly in Confined Channels
Micromachines 2015, 6(9), 1331-1345; https://doi.org/10.3390/mi6091331 - 10 Sep 2015
Cited by 5
Abstract
We report on the microfluidic induced monodispersed microdroplet generation and assembly in confined microchannels. Two and three dimensional close-packed droplet lattices were obtained in microfluidic devices by adjusting the channel geometry, the fluidic flow rates and the monodispersed droplet size. The droplet packing [...] Read more.
We report on the microfluidic induced monodispersed microdroplet generation and assembly in confined microchannels. Two and three dimensional close-packed droplet lattices were obtained in microfluidic devices by adjusting the channel geometry, the fluidic flow rates and the monodispersed droplet size. The droplet packing was mainly caused by the volumetric effect and capillarity in confined microchannels. Polymerizable fluids were also investigated to demonstrate the effect of fluidic properties on the microdroplet generation and assembly, which could find interesting applications in the future. This approach would be helpful to fundamentally understand the mechanism of self-assembly process of particles in confined microstructures, and practically be applied in sensing and energy storage devices. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Ultra-Portable Smartphone Controlled Integrated Digital Microfluidic System in a 3D-Printed Modular Assembly
Micromachines 2015, 6(9), 1289-1305; https://doi.org/10.3390/mi6091289 - 07 Sep 2015
Cited by 15
Abstract
Portable sensors and biomedical devices are influenced by the recent advances in microfluidics technologies, compact fabrication techniques, improved detection limits and enhanced analysis capabilities. This paper reports the development of an integrated ultraportable, low-cost, and modular digital microfluidic (DMF) system and its successful [...] Read more.
Portable sensors and biomedical devices are influenced by the recent advances in microfluidics technologies, compact fabrication techniques, improved detection limits and enhanced analysis capabilities. This paper reports the development of an integrated ultraportable, low-cost, and modular digital microfluidic (DMF) system and its successful integration with a smartphone used as a high-level controller and post processing station. Low power and cost effective electronic circuits are designed to generate the high voltages required for DMF operations in both open and closed configurations (from 100 to 800 V). The smartphone in turn commands a microcontroller that manipulate the voltage signals required for droplet actuation in the DMF chip and communicates wirelessly with the microcontroller via Bluetooth module. Moreover, the smartphone acts as a detection and image analysis station with an attached microscopic lens. The holder assembly is fabricated using three-dimensional (3D) printing technology to facilitate rapid prototyping. The holder features a modular design that enables convenient attachment/detachment of a variety of DMF chips to/from an electrical busbar. The electrical circuits, controller and communication system are designed to minimize the power consumption in order to run the device on small lithium ion batteries. Successful controlled DMF operations and a basic colorimetric assay using the smartphone are demonstrated. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Centrifugal Step Emulsification can Produce Water in Oil Emulsions with Extremely High Internal Volume Fractions
Micromachines 2015, 6(8), 1180-1188; https://doi.org/10.3390/mi6081180 - 20 Aug 2015
Cited by 8
Abstract
The high throughput preparation of emulsions with high internal volume fractions is important for many different applications, e.g., drug delivery. However, most emulsification techniques reach only low internal volume fractions and need stable flow rates that are often difficult to control. Here, we [...] Read more.
The high throughput preparation of emulsions with high internal volume fractions is important for many different applications, e.g., drug delivery. However, most emulsification techniques reach only low internal volume fractions and need stable flow rates that are often difficult to control. Here, we present a centrifugal high throughput step emulsification disk for the fast and easy production of emulsions with high internal volume fractions above 95%. The disk produces droplets at generation rates of up to 3700 droplets/s and, for the first time, enables the generation of emulsions with internal volume fractions of >97%. The coefficient of variation between droplet sizes is very good (4%). We apply our system to show the in situ generation of gel emulsion. In the future, the recently introduced unit operation of centrifugal step emulsification may be used for the high throughput production of droplets as reaction compartments for clinical diagnostics or as starting material for micromaterial synthesis. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
A Concentration-Controllable Microfluidic Droplet Mixer for Mercury Ion Detection
Micromachines 2015, 6(7), 915-925; https://doi.org/10.3390/mi6070915 - 13 Jul 2015
Cited by 2
Abstract
A microfluidic droplet mixer is developed for rapid detection of Hg(II) ions. Reagent concentration and droplets can be precisely controlled by adjusting the flow rates of different fluid phases. By selecting suitable flow rates of the oil phase, probe phase and sample phase, [...] Read more.
A microfluidic droplet mixer is developed for rapid detection of Hg(II) ions. Reagent concentration and droplets can be precisely controlled by adjusting the flow rates of different fluid phases. By selecting suitable flow rates of the oil phase, probe phase and sample phase, probe droplets and sample droplets can be matched and merged in pairs and subsequently well-mixed in the poly (dimethylsiloxane) (PDMS) channels. The fluorescence enhancement probe (Rhodamine B mixed with gold nanoparticles) encapsulated in droplets can react with Hg(II) ions. The Hg(II) ion concentration in the sample droplets is adjusted from about 0 to 1000 nM through fluid regulation to simulate possible various contaminative water samples. The intensity of the emission fluorescence is sensitive to Hg(II) ions (increases as the Hg(II) ion concentration increases). Through the analysis of the acquired fluorescence images, the concentration of Hg(II) ions can be precisely detected. With the advantages of less time, cost consumption and easier manipulations, this device would have a great potential in micro-scale sample assays and real-time chemical reaction studies. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Dynamics of Electrowetting Droplet Motion in Digital Microfluidics Systems: From Dynamic Saturation to Device Physics
Micromachines 2015, 6(6), 778-789; https://doi.org/10.3390/mi6060778 - 19 Jun 2015
Cited by 15
Abstract
A quantitative description of the dynamics of droplet motion has been a long-standing concern in electrowetting research. Although many static and dynamic models focusing on droplet motion induced by electrowetting-on-dielectric (EWOD) already exist, some dynamic features do not fit these models well, especially [...] Read more.
A quantitative description of the dynamics of droplet motion has been a long-standing concern in electrowetting research. Although many static and dynamic models focusing on droplet motion induced by electrowetting-on-dielectric (EWOD) already exist, some dynamic features do not fit these models well, especially the dynamic saturation phenomenon. In this paper, a dynamic saturation model of droplet motion on the single-plate EWOD device is presented. The phenomenon that droplet velocity is limited by a dynamic saturation effect is precisely predicted. Based on this model, the relationship between droplet motion and device physics is extensively discussed. The static saturation phenomenon is treated with a double-layer capacitance electric model, and it is demonstrated as one critical factor determining the dynamics of droplet motion. This work presents the relationship between dynamics of electrowetting induced droplet motion and device physics including device structure, surface material and interface electronics, which helps to better understand electrowetting induced droplet motions and physics of digital microfluidics systems. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle
Formation of Polymeric Hollow Microcapsules and Microlenses Using Gas-in-Organic-in-Water Droplets
Micromachines 2015, 6(5), 622-633; https://doi.org/10.3390/mi6050622 - 21 May 2015
Cited by 5
Abstract
This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic [...] Read more.
This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Review

Jump to: Research

Open AccessReview
Droplet Manipulations in Two Phase Flow Microfluidics
Micromachines 2015, 6(11), 1768-1793; https://doi.org/10.3390/mi6111455 - 13 Nov 2015
Cited by 33
Abstract
Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of [...] Read more.
Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of new techniques, whose potential has not been fully realized. This review summarizes the currently existing techniques for manipulating droplets in two-phase flow microfluidics. Specifically, very recent developments like the use of acoustic waves, magnetic fields, surface energy wells, and electrostatic traps and rails are discussed. The physical principles are explained, and (potential) advantages and drawbacks of different methods in the sense of versatility, flexibility, tunability and durability are discussed, where possible, per technique and per droplet operation: generation, transport, sorting, coalescence and splitting. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessReview
Recent Advances in Applications of Droplet Microfluidics
Micromachines 2015, 6(9), 1249-1271; https://doi.org/10.3390/mi6091249 - 02 Sep 2015
Cited by 52
Abstract
Droplet-based microfluidics is a colloidal and interfacial system that has rapidly progressed in the past decade because of the advantages of low fabrication costs, small sample volumes, reduced analysis durations, high-throughput analysis with exceptional sensitivity, enhanced operational flexibility, and facile automation. This technology [...] Read more.
Droplet-based microfluidics is a colloidal and interfacial system that has rapidly progressed in the past decade because of the advantages of low fabrication costs, small sample volumes, reduced analysis durations, high-throughput analysis with exceptional sensitivity, enhanced operational flexibility, and facile automation. This technology has emerged as a new tool for many recently used applications in molecular detection, imaging, drug delivery, diagnostics, cell biology and other fields. Herein, we review recent applications of droplet microfluidics proposed since 2013. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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