Dynamics of molecular transport by surfactants in emulsions

Skhiri, Yousr; Gruner, Philipp; Semin, Benoît; Brosseau, Quentin; Pekin, Deniz; Mažutis, Linas; Goust, Victoire; Kleinschmidt, Felix; Harrak, Abdeslam El; Hutchison, J. Brian; Mayot, Estelle; Bartolo, Jean-François; Griffiths, Andrew D.; Taly, Valérie; Baret, Jean‐Christophe

doi:10.1039/c2sm25934f

Cited by 135 publications

(223 citation statements)

References 44 publications

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“…Our and other studies of surfactant distribution 39,40 show that the kinetics of surfactant equilibrium on a surface dictate three distinct temporal regimes for the droplet interface. In the primary, or denuded, regime, such as when the droplet is first formed, the droplet surface is largely bare of surfactant.…”

Section: Resultsmentioning

confidence: 99%

“…Comparable studies using dynamic light scattering (DLS) measurements suggest a size for EA surfactant stable inflated micelles of approximately 120 nm. 40 In the absence of other supporting data, it is clear that there is a broad agreement on length scales but that further work needs to be done to resolve the variability in these measurements. This graph of chemical potential explains the droplet shrinkage, micelle formation and, to some extent, budding failure modes described subsequently.…”

Section: Resultsmentioning

confidence: 99%

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Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

2015

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The applicability of droplet-based microfluidic systems to many research fields stems from the fact that droplets are generally considered individual and selfcontained reaction vessels. This study demonstrates that, more often than not, the integrity of droplets is not complete, and depends on a range of factors including surfactant type and concentration, the micro-channel surface, droplet storage conditions, and the flow rates used to form and process droplets. Herein, a model microfluidic device is used for droplet generation and storage to allow the comparative study of forty-four different oil/surfactant conditions. Assessment of droplet stability under these conditions suggests a diversity of different droplet failure modes. These failure modes have been classified into families depending on the underlying effect, with both numerical and qualitative models being used to describe the causative effect and to provide practical solutions for droplet failure amelioration in microfluidic systems. V C 2015 AIP Publishing LLC.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

2015

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“…The greatest challenge with emulsion-based screening is finding a fluorescent assay for one's particular enzyme of interest. It is important to note that some small-molecule dyes readily exchange between emulsion droplets and limit the ability to resolve functional differences (38).…”

Section: Discussionmentioning

confidence: 99%

Dissecting enzyme function with microfluidic-based deep mutational scanning

Romero

Tran

Abate

2015

Proc. Natl. Acad. Sci. U.S.A.

203

169

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Natural enzymes are incredibly proficient catalysts, but engineering them to have new or improved functions is challenging due to the complexity of how an enzyme's sequence relates to its biochemical properties. Here, we present an ultrahigh-throughput method for mapping enzyme sequence-function relationships that combines droplet microfluidic screening with next-generation DNA sequencing. We apply our method to map the activity of millions of glycosidase sequence variants. Microfluidic-based deep mutational scanning provides a comprehensive and unbiased view of the enzyme function landscape. The mapping displays expected patterns of mutational tolerance and a strong correspondence to sequence variation within the enzyme family, but also reveals previously unreported sites that are crucial for glycosidase function. We modified the screening protocol to include a hightemperature incubation step, and the resulting thermotolerance landscape allowed the discovery of mutations that enhance enzyme thermostability. Droplet microfluidics provides a general platform for enzyme screening that, when combined with DNAsequencing technologies, enables high-throughput mapping of enzyme sequence space.protein engineering | droplet-based microfluidics | high-throughput DNA sequencing E nzymes are powerful biological catalysts capable of remarkably accelerating the rates of chemical transformations (1). The molecular bases of these rate accelerations are often complex, using multiple steps, multiple catalytic mechanisms, and relying on numerous molecular interactions, in addition to those provided by the main catalytic groups. This complexity imposes a significant barrier to understanding how an enzyme's sequence impacts its function and, thus, on our ability to rationally design biocatalysts with new or enhanced functions (2-4).Comprehensive mappings of sequence-function relationships can be used to dissect the molecular basis of protein function in an unbiased manner (5). Growth selections or in vitro binding screens can be combined with next-generation DNA sequencing to generate detailed mappings between a protein's sequence and its biochemical properties, such as binding affinity, enzymatic activity, and stability (6-9). This deep mutational scanning approach has been used to study the structure of the protein fitness landscape, discover new functional sites, improve molecular energy functions, and identify beneficial combinations of mutations for protein engineering. However, these methods rely on functional assays coupled to cell growth or protein binding, severely limiting the types of proteins that can be analyzed. For example, most enzymes of biological or industrial relevance cannot be analyzed using existing methods because they do not catalyze a reaction that can be directly coupled to cell growth. Experimental advances are needed to broaden the applicability of deep mutational scanning to the diverse palette of functions performed by enzymes.In this paper, we present a general method for mapping protein sequence-func...

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“…The kinetic stabilization of emulsions occurs through several mechanisms, involving electrostatic or steric repulsion and the buildup of Marangoni stresses to improve the lifetime of emulsions against coalescence (12, 13). On the other hand, surfactants are involved in transport processes such as Ostwald ripening or solute transport, which mediates the chemical equilibration of the system (14-17): in general, all processes affecting the lifetime of emulsions (coalescence, rupture, exchange, and loss of molecules) are directly related to the physics and dynamics of the surfactant molecules at interfaces (3,4,6,10,11,15,16). The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19).…”

mentioning

confidence: 99%

Surfactant adsorption kinetics in microfluidics

Riechers

Maes

Akoury

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Emulsions are metastable dispersions. Their lifetimes are directly related to the dynamics of surfactants. We design a microfluidic method to measure the kinetics of adsorption of surfactants to the droplet interface, a key process involved in foaming, emulsification, and droplet coarsening. The method is based on the pH decay in the droplet as a direct measurement of the adsorption of a carboxylic acid surfactant to the interface. From the kinetic measurement of the bulk equilibration of the pH, we fully determine the adsorption process of the surfactant. The small droplet size and the convection during the droplet flow ensure that the transport of surfactant through the bulk is not limiting the kinetics of adsorption. To validate our measurements, we show that the adsorption process determines the timescale required to stabilize droplets against coalescence, and we show that the interface should be covered at more than 90% to prevent coalescence. We therefore quantitatively link the process of adsorption/desorption, the stabilization of emulsions, and the kinetics of solute partitioning-here through ion exchange-unraveling the timescales governing these processes. Our method can be further generalized to other surfactants, including nonionic surfactants, by making use of fluorophore-surfactant interactions.droplet | interfaces | surfactant | emulsion | microfluidics S urface active compounds are ubiquitous in our daily life, be it in living systems or in industrial and technological products (1-3). The compounds are used widely for the stabilization of foams and emulsions for food and cosmetic products, painting materials, and industrial coatings (3). Emulsions are nowadays also used in combination with microfluidic systems for applications in biotechnology (3-11). An emulsion is a dispersion of one liquid phase into another, stabilized by surfactants in a metastable state. The kinetic stabilization of emulsions occurs through several mechanisms, involving electrostatic or steric repulsion and the buildup of Marangoni stresses to improve the lifetime of emulsions against coalescence (12, 13). On the other hand, surfactants are involved in transport processes such as Ostwald ripening or solute transport, which mediates the chemical equilibration of the system (14-17): in general, all processes affecting the lifetime of emulsions (coalescence, rupture, exchange, and loss of molecules) are directly related to the physics and dynamics of the surfactant molecules at interfaces (3,4,6,10,11,15,16). The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19). From this point, a wide variety of models describe the adsorption dynamics, accounting for all kinds of molecular effects at interfaces (20-26). We expect two limiting cases: (i) the adsorption is limited by the bulk transport toward the interface, leading to a local equilibrium between the surfactant interfacial concen...

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Dynamics of molecular transport by surfactants in emulsions

Cited by 135 publications

References 44 publications

Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

Dissecting enzyme function with microfluidic-based deep mutational scanning

Surfactant adsorption kinetics in microfluidics

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