1,721,034 research outputs found
Electro-coalescence of digitally controlled droplets
No full textIn this paper we describe a universal mechanism for merging multiple aqueous microdroplets within a flowing stream consisting of an oil carrier phase. Our approach involves the use of both a pillar array acting as a passive merging element, as well as built-in electrodes acting as an active merging element. The pillar array enables slowing down and trapping of the droplets via the drainage of the oil phase. This brings adjacent droplets into close proximity. At this point, an electric field applied to the electrodes breaks up the thin oil film surrounding the droplets resulting in merging
Pillar-induced droplet merging in microfluidic circuits
No full textA novel method is presented for controllably merging aqueous microdroplets within segmented flow microfluidic devices. Our approach involves exploiting the difference in hydrodynamic resistance of the continuous phase and the surface tension of the discrete phase through the use of passive structures contained within a microfluidic channel. Rows of pillars separated by distances smaller than the representative droplet dimension are installed within the fluidic network and define passive merging elements or chambers. Initial experiments demonstrate that such a merging element can controllably adjust the distance between adjacent droplets. In a typical scenario, a droplet will enter the chamber, slow down and stop. It will wait and then merge with the succeeding droplets until the surface tension is overwhelmed by the hydraulic pressure. We show that such a merging process is independent of the inter-droplet separation but rather dependent on the droplet size. Moreover, the number of droplets that can be merged at any time is also dependent on the mass flow rate and volume ratio between the droplets and the merging chamber. Finally, we note that the merging of droplet interfaces occurs within both compressing and the decompressing regimes
Controlled one dimensional oscillation of the Belousov–Zhabotinsky reaction confined within microchannels
No full textThe Belousov-Zhabotinsky reaction was performed in microdroplets confined in rectangular microchannels. In addition to producing one-dimensional waves, the reaction showed an increase in oscillation frequency thought to be mainly due to bromine diffusion out of the microdroplets. We found that surfactant loaded mineral oil can be used as an encapsulation agent to not only extend the stable reaction time from 200 s to approximately 800 s, but more importantly to further extend the one-dimensional wave formation from ∼15 s to 800 s. © 2012 The Royal Society of Chemistry.link_to_subscribed_fulltex
A microdroplet dilutor for high-throughput screening
No full textPipetting and dilution are universal processes used in chemical and biological laboratories to assay and experiment. In microfluidics such operations are equally in demand, but difficult to implement. Recently, droplet-based microfluidics has emerged as an exciting new platform for high-throughput experimentation. However, it is challenging to vary the concentration of droplets rapidly and controllably. To this end, we developed a dilution module for high-throughput screening using droplet-based microfluidics. Briefly, a nanolitre-sized sample droplet of defined concentration is trapped within a microfluidic chamber. Through a process of droplet merging, mixing and re-splitting, this droplet is combined with a series of smaller buffer droplets to generate a sequence of output droplets that define a digital concentration gradient. Importantly, the formed droplets can be merged with other reagent droplets to enable rapid chemical and biological screens. As a proof of concept, we used the dilutor to perform a high-throughput homogeneous DNA-binding assay using only nanolitres of sample
Microfluidic evaporator for on-chip sample concentration
No full textWe present a simple technique for the concentration of liquid samples in microfluidic devices applicable for single or multiple-phase configurations. The strategy consists of capturing the sample of interest within microfluidic traps and breaking its continuity by the introduction of a gas phase, which is also used to evaporate it.sponsorship: This work was supported in part by a RCUK basic technology and platform grant. JBE acknowledges the receipt of an ERC starting investigator grant. (RCUK basic technology and platform grant, ERC starting investigator grant, EPSRC|EP/H046593/1, EPSRC|EP/C013174/1, EPSRC|EP/D048664/1, Engineering and Physical Sciences Research Council|EP/D048664/1, Engineering and Physical Sciences Research Council|EP/H046593/1, Engineering and Physical Sciences Research Council|EP/C013174/1)status: Publishe
Droplet-interfaced microchip and capillary electrophoretic separations
No full textBoth capillary and chip-based electrophoresis are powerful separation methods widely used for the separation of complex analytical mixtures in the fields of genomics, proteomics, metabolomics, and cellular analysis. However their utility as basic tools in high-throughput analysis and multidimensional separations has been hampered by inefficient or biased sample injection methods. Herein, we address this problem through the development of a simple separation platform that incorporates droplet-based microfluidic module for the encapsulation of analytes prior to the analytical separation. This method allows for the precise and reproducible injection of pL to nL volume isolated plugs into an electrophoretic separation channel. The developed platform is free from inter sample contamination, allows for small sample size, high-throughput analysis, and can provide quantitative analytical informatio
Compartmentalization of electrophoretically separated analytes in a multiphase microfluidic platform
No full textHerein, we describe the monolithic integration of a multiphase microfluidic system to a microcapillary gel electrophoresis (?CGE) architecture for the complete isolation and storage of separated analyte bands. Within this platform, analyte molecules are separated using microchannel gel electrophoresis, and the eluted bands are stored in a sequence of approximately 40?600 encapsulating microdroplets. Importantly, employing such a system allows for total control of droplet size, shape, and composition. This approach is utilized to separate, optically detect, and encapsulate two fluorescent analytes from a composite sample mixture. Further to this, we subsequently investigate the potential of the system to be used as a concentration gradient generator through analysis of the segmented analyte bands and droplet composition
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fluorescence detection methods for microfluidic droplet platforms
No full textThe development of microfluidic platforms for performing chemistry and biology has in large part been driven by a range of potential benefits that accompany system miniaturisation. Advantages include the ability to efficiently process nano- to femoto- liter volumes of sample, facile integration of functional components, an intrinsic predisposition towards large-scale multiplexing, enhanced analytical throughput, improved control and reduced instrumental footprints.In recent years much interest has focussed on the development of droplet-based (or segmented flow) microfluidic systems and their potential as platforms in high-throughput experimentation. Here water-in-oil emulsions are made to spontaneously form in microfluidic channels as aresult of capillary instabilities between the two immiscible phases. Importantly, microdroplets of precisely defined volumes and compositions can be generated at frequencies of several kHz. Furthermore, by encapsulating reagents of interest within isolated compartments separated by a continuous immiscible phase, both sample cross-talk and dispersion (diffusion- and Taylor-based) can be eliminated, which leads to minimal cross-contamination and the ability to time analytical processes with great accuracy. Additionally, since there is no contact between the contents of the droplets and the channel walls (which are wetted by the continuous phase) absorption and loss of reagents on the channel walls is prevented. Once droplets of this kind have been generated and processed, it is necessary to extract the required analytical information. In this respect the detection method of choice should be rapid, provide high-sensitivity and low limits of detection, be applicable to a range of molecular species, be non-destructive and be able to be integrated with microfluidic devices in a facile manner. To address this need we have developed a suite of experimental tools and protocols that enable the extraction of large amounts of photophysical information from small-volume environments, and are applicable to the analysis of a wide range of physical, chemical and biological parameters. Herein two examples of these methods are presented and applied to the detection of single cells and the mapping of mixing processes inside picoliter-volume droplets. We report the entire experimental process including microfluidic chip fabrication, the optical setup and the process of droplet generation and detection
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