Parallel synchronization of two trains of droplets using a railroad-like channel network

Ahn, Byungwook; Lee, Kangsun; Lee, Hun; Panchapakesan, Rajagopal; Oh, Kwang W.

doi:10.1039/c1lc20690g

Cited by 45 publications

(45 citation statements)

References 17 publications

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“…Increasing efforts have been invested into understanding the underlying science and engineering principles of droplet microfluidics 5,[15][16][17][18] and exploring new approaches and devices to address the challenges in biological and medical applications 10,[19][20][21] . For example, microfluidic circuits have been demonstrated for droplet injection, 22 steering, 23 trapping and release, 24 synchronization, 25 fusion, 26 and sorting, 27 leading to a much broader spectrum of applications, including digital PCR, 28 protein engineering and direct evolution, 29 and drug screening. 30 As droplet microfluidics evolves, precise and controllable droplet generation has been recognized as an important component in developing droplet-based platforms for biological and medical applications.…”

Section: Introductionmentioning

confidence: 99%

Programmable active droplet generation enabled by integrated pneumatic micropumps

2013

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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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Section: Introductionmentioning

confidence: 99%

Programmable active droplet generation enabled by integrated pneumatic micropumps

2013

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“…The maximum efficiency of 94% was achieved at the optimized flow rate ratio of Q Ratio ¼ 0.85 (case C). As detailed in our previous studies, if the droplet length and the generation frequency are perfectly matched, 100% synchronization efficiency can be attainable, 39,40 after the seamless electrocoalescence at the X-shape junction. In the electrocoalescence, two failure mechanisms were observed as shown in Fig.…”

Section: Resultsmentioning

confidence: 97%

“…In order to perform the parallel synchronization of droplets, the ladder-like channel network was used in which the top and bottom channels were interconnected with narrow fluidic channels. 39,40 The mechanism of synchronization relies on the automatic tuning of velocity of droplets due to the pressure difference between the two channels. As the droplets pass through the ladder-like channel network, the existing pressure difference caused by the droplets squeezed between the channels (top and bottom channel width: 200 lm) allows the oil phase to flow through the narrow fluidic channels until the pressure is matched.…”

Section: Resultsmentioning

confidence: 99%

“…38 (iii) The sample droplets are introduced into a ladder-like channel network to make them synchronized with the washing buffer droplets. 39,40 The droplet synchronization unit enables the two trains of the droplets to be merged laterally. (iv) The two parallel-synchronized droplets are merged at an entrance of the X-shape separation junction by an electric field, which can lead to destabilization of the surface of the droplets to be easily merged.…”

Section: Experimental a Working Principlementioning

confidence: 99%

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Droplet-based microfluidic washing module for magnetic particle-based assays

Lee

2014

Biomicrofluidics

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In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The dropletbased washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets. To realize the droplet-based washing function, the following four procedures were sequentially carried in a droplet-based microfluidic device: parallel synchronization of two trains of droplets by using a ladder-like channel network; lateral electrocoalescence by an electric field; magnetic particle manipulation by a magnetic field; and asymmetrical splitting of merged droplets. For the stable droplet synchronization and electrocoalescence, we optimized droplet generation conditions by varying the flow rate ratio (or droplet size). Image analysis was carried out to determine the fluorescent intensity of reagents before and after the washing step. As a result, the unbound reagents in sample droplets were significantly removed by more than a factor of 25 in the single washing step, while the magnetic particles were successfully extracted into washing buffer droplets. As a proof-of-principle, we demonstrate a magnetic particle-based immunoassay with streptavidin-coated magnetic particles and fluorescently labelled biotin in the proposed continuous flow dropletbased microfluidic platform. V C 2014 AIP Publishing LLC.

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“…Current versions of ladders have fore-aft structural symmetry due to equally-spaced vertical bypasses. Such symmetric ladders are limited in functionality because the distance between pairs of drops have been shown to decrease at the exit only for constant inlet flow [11][12][13] . Since flexible manipulation of drop spacing in networks is crucial for passively regulating a variety of tasks including drop coalescence 14 , detection and storage, there is a need to design microfluidic ladders with multiple functionalities.…”

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confidence: 99%

Traffic of pairs of drops in microfluidic ladder networks with fore-aft structural asymmetry

Maddala¹,

Wang²,

Vanapalli³

et al. 2012

Microfluid Nanofluid

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We investigate the dynamics of pairs of drops in microfluidic ladder networks with slanted bypasses, which break the fore-aft structural symmetry. Our analytical results indicate that unlike symmetric ladder networks, structural asymmetry introduced by a single slanted bypass can be used to modulate the relative drop spacing, enabling them to contract, synchronize, expand, or even flip at the ladder exit. Our experiments confirm all these behaviors predicted by theory. Numerical analysis further shows that while ladder networks containing several identical bypasses are limited to nearly linear transformation of input delay between drops, combination of forward and backward slant bypasses can cause significant non-linear transformation enabling coding and decoding of input delays.Understanding the spatiotemporal dynamics of confined immiscible plugs in interconnected fluidic paths is essential for applications ranging from lab-on-chip technologies 1,2 to physiological flows 3 to porous media flows 4 . The traffic of drops or bubbles in even simple networks such as bifurcating channels can be astonishingly complex due to collective hydrodynamic resistive interactions in the branches [5][6][7] . Although such intricate dynamics, in the case of lab-on-chip applications, make device design challenging, the collective behaviors can be harnessed to perform useful tasks such as droplet sorting 8 and storage 9,10 . Recently, the collective dynamics between pairs of drops have been harnessed in the so-called microfluidic ladder networks (MLNs) to control their relative drop spacing 11 . In MLNs, two droplet-carrying parallel channels are connected by narrow bypass channels through which the motion of drops is forbidden but the carrier fluid can leak. Current versions of ladders have fore-aft structural symmetry due to equally-spaced vertical bypasses. Such symmetric ladders are limited in functionality because the distance between pairs of drops have been shown to decrease at the exit only for constant inlet flow [11][12][13] . Since flexible manipulation of drop spacing in networks is crucial for passively regulating a variety of tasks including drop coalescence 14 , detection and storage, there is a need to design microfluidic ladders with multiple functionalities.From a fundamental perspective, the dynamics of drops in MLNs is distinct compared to the widely-studied microfluidic loops 5,7,13,15 . In loops, drops at junctions choose a given branch. These discrete choices make such systems non-linear, enabling coding and decoding of input signals. Since drops do not typically make decisions at the bypass junctions in ladders, an open question is: is it possible to design microlfuidic ladders that yield significant non-linear transformation of input signal?In this Letter, we study the dynamics of spacing between drop pairs in MLNs with slanted bypasses. We find that because the slant breaks the fore-aft symmetry, it provides significantly more control over drop spacing than symmetric MLNs. We also discover that inclusion ...

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Parallel synchronization of two trains of droplets using a railroad-like channel network

Cited by 45 publications

References 17 publications

Programmable active droplet generation enabled by integrated pneumatic micropumps

Programmable active droplet generation enabled by integrated pneumatic micropumps

Droplet-based microfluidic washing module for magnetic particle-based assays

Traffic of pairs of drops in microfluidic ladder networks with fore-aft structural asymmetry

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