1
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Gantz M, Neun S, Medcalf EJ, van Vliet LD, Hollfelder F. Ultrahigh-Throughput Enzyme Engineering and Discovery in In Vitro Compartments. Chem Rev 2023; 123:5571-5611. [PMID: 37126602 PMCID: PMC10176489 DOI: 10.1021/acs.chemrev.2c00910] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Novel and improved biocatalysts are increasingly sourced from libraries via experimental screening. The success of such campaigns is crucially dependent on the number of candidates tested. Water-in-oil emulsion droplets can replace the classical test tube, to provide in vitro compartments as an alternative screening format, containing genotype and phenotype and enabling a readout of function. The scale-down to micrometer droplet diameters and picoliter volumes brings about a >107-fold volume reduction compared to 96-well-plate screening. Droplets made in automated microfluidic devices can be integrated into modular workflows to set up multistep screening protocols involving various detection modes to sort >107 variants a day with kHz frequencies. The repertoire of assays available for droplet screening covers all seven enzyme commission (EC) number classes, setting the stage for widespread use of droplet microfluidics in everyday biochemical experiments. We review the practicalities of adapting droplet screening for enzyme discovery and for detailed kinetic characterization. These new ways of working will not just accelerate discovery experiments currently limited by screening capacity but profoundly change the paradigms we can probe. By interfacing the results of ultrahigh-throughput droplet screening with next-generation sequencing and deep learning, strategies for directed evolution can be implemented, examined, and evaluated.
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Affiliation(s)
- Maximilian Gantz
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd, Cambridge CB2 1GA, U.K
| | - Stefanie Neun
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd, Cambridge CB2 1GA, U.K
| | - Elliot J Medcalf
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd, Cambridge CB2 1GA, U.K
| | - Liisa D van Vliet
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd, Cambridge CB2 1GA, U.K
| | - Florian Hollfelder
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd, Cambridge CB2 1GA, U.K
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2
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Payne EM, Taraji M, Murray BE, Holland-Moritz DA, Moore JC, Haddad PR, Kennedy RT. Evaluation of Analyte Transfer between Microfluidic Droplets by Mass Spectrometry. Anal Chem 2023; 95:4662-4670. [PMID: 36862378 DOI: 10.1021/acs.analchem.2c04985] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Abstract
Droplet microfluidics enables high-throughput experimentation and screening by encapsulating chemical and biochemical samples in aqueous droplets segmented by an immiscible fluid. In such experiments, it is critical that each droplet remains chemically distinct. A common approach is to use fluorinated oils with surfactants to stabilize droplets. However, some small molecules have been observed to transport between droplets under these conditions. Attempts to study and mitigate this effect have relied on evaluating crosstalk using fluorescent molecules, which inherently limits the analyte scope and conclusions drawn about the mechanism of the effect. In this work, transport of low molecular weight compounds between droplets was investigated using electrospray ionization mass spectrometry (ESI-MS) for measurement. The use of ESI-MS significantly expands the scope of analytes that can be tested. We tested 36 structurally diverse analytes that were found to exhibit crosstalk ranging from negligible to complete transfer using HFE 7500 as the carrier fluid and 008-fluorosurfactant as a surfactant. Using this data set, we developed a predictive tool showing that high log P and log D values correlate with high crosstalk, and high polar surface area and log S correlate with low crosstalk. We then investigated several carrier fluids, surfactants, and flow conditions. It was discovered that transport is strongly dependent on all of these factors and that experimental design and surfactant tailoring can reduce carryover. We present evidence for mixed crosstalk mechanisms including both micellar and oil partitioning transfer. By understanding the driving mechanisms, surfactant and oil compositions can be designed to better reduce chemical transport for screening workflows.
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Affiliation(s)
- Emory M Payne
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48103, United States
| | - Maryam Taraji
- The Australian Wine Research Institute, Adelaide, South Australia 5064, Australia.,Metabolomics Australia, Adelaide, South Australia 5064, Australia.,School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7005, Australia
| | - Bridget E Murray
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48103, United States
| | - Daniel A Holland-Moritz
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Jeffrey C Moore
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Paul R Haddad
- School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7005, Australia
| | - Robert T Kennedy
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48103, United States
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3
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A novel high-throughput approach for transforming filamentous fungi employing a droplet-based microfluidic platform. N Biotechnol 2022; 72:149-158. [PMID: 36442794 DOI: 10.1016/j.nbt.2022.11.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 11/16/2022] [Accepted: 11/18/2022] [Indexed: 11/27/2022]
Abstract
Droplet-based microfluidic technology is a powerful tool for single-cell cultivation and rapid isolation of bacteria, yeasts and algae. However, it has been of limited use for studies of filamentous fungi due to the fast growth of their branched hyphae. The long regeneration time for fungal protoplasts and low-throughput screening methods are inherent problems for current genetic transformation techniques. Therefore, we have developed a novel droplet-based method for the filamentous fungus Trichoderma reesei expressing green fluorescent protein (GFP) as a marker. This approach presented several outstanding advantages over the traditional transformation method, including a 7-fold reduction in time for T. reesei protoplast regeneration, an 8-fold increase in regeneration frequency, and a screening speed of up to 8,000 droplets min-1. In this study, we encapsulated and incubated the gfp-transformed T. reesei protoplasts in droplets for 24 h, screened the droplets in a high-throughput assay, and eventually collected a transformant library with over 96 % of the candidates transformed with the marker gene. This versatile approach should make fungi more amenable to genetic manipulation and encourage strain improvements for industrial applications.
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4
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Sahin MA, Werner H, Udani S, Di Carlo D, Destgeer G. Flow lithography for structured microparticles: fundamentals, methods and applications. LAB ON A CHIP 2022; 22:4007-4042. [PMID: 35920614 DOI: 10.1039/d2lc00421f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Structured microparticles, with unique shapes, customizable sizes, multiple materials, and spatially-defined chemistries, are leading the way for emerging 'lab on a particle' technologies. These microparticles with engineered designs find applications in multiplexed diagnostics, drug delivery, single-cell secretion assays, single-molecule detection assays, high throughput cytometry, micro-robotics, self-assembly, and tissue engineering. In this article we review state-of-the-art particle manufacturing technologies based on flow-assisted photolithography performed inside microfluidic channels. Important physicochemical concepts are discussed to provide a basis for understanding the fabrication technologies. These photolithography technologies are compared based on the structural as well as compositional complexity of the fabricated particles. Particles are categorized, from 1D to 3D particles, based on the number of dimensions that can be independently controlled during the fabrication process. After discussing the advantages of the individual techniques, important applications of the fabricated particles are reviewed. Lastly, a future perspective is provided with potential directions to improve the throughput of particle fabrication, realize new particle shapes, measure particles in an automated manner, and adopt the 'lab on a particle' technologies to other areas of research.
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Affiliation(s)
- Mehmet Akif Sahin
- Control and Manipulation of Microscale Living Objects, Central Institute for Translational Cancer Research (TranslaTUM), Department of Electrical and Computer Engineering, Technical University of Munich, Einsteinstraße 25, Munich 81675, Germany.
| | - Helen Werner
- Control and Manipulation of Microscale Living Objects, Central Institute for Translational Cancer Research (TranslaTUM), Department of Electrical and Computer Engineering, Technical University of Munich, Einsteinstraße 25, Munich 81675, Germany.
| | - Shreya Udani
- Department of Bioengineering, University of California, Los Angeles, California 90095, USA.
| | - Dino Di Carlo
- Department of Bioengineering, University of California, Los Angeles, California 90095, USA.
- Department of Mechanical and Aerospace Engineering, California NanoSystems Institute and Jonsson Comprehensive Cancer Center, University of California, Los Angeles, California 90095, USA
| | - Ghulam Destgeer
- Control and Manipulation of Microscale Living Objects, Central Institute for Translational Cancer Research (TranslaTUM), Department of Electrical and Computer Engineering, Technical University of Munich, Einsteinstraße 25, Munich 81675, Germany.
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5
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Nakamura A, Honma N, Tanaka Y, Suzuki Y, Shida Y, Tsuda Y, Hidaka K, Ogasawara W. 7-Aminocoumarin-4-acetic Acid as a Fluorescent Probe for Detecting Bacterial Dipeptidyl Peptidase Activities in Water-in-Oil Droplets and in Bulk. Anal Chem 2021; 94:2416-2424. [PMID: 34963280 PMCID: PMC8886566 DOI: 10.1021/acs.analchem.1c04108] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
![]()
Droplet-based
microfluidic systems are a powerful tool for biological
assays with high throughput. Water-in-oil droplets (WODLs) are typically
used in droplet-based microfluidic systems to culture microorganisms
and perform enzyme assays. However, because of the oil surrounding
the nanoliter and picoliter volumes of WODLs, availability of suitable
substrates is limited. For instance, although 7-amino-4-methylcoumarin
(AMC) is commonly used as a fluorescent probe of the substrate to
detect peptidase activity, AMC leaks from WODLs to the oil phase due
to its high hydrophobicity. Thus, AMC substrates cannot be used in
droplet-based microfluidic systems with WODLs. In this study, we developed
a peptidase substrate consisting of a dipeptide and 7-aminocoumarin-4-acetic
acid (ACA), an AMC-derived fluorogenic compound. ACA was retained
in the WODL for more than 7 days, and the dipeptidyl ACA substrate
detected dipeptidyl peptidase (DPP) activity in the WODL. Compared
to AMC substrates, the substrate specificity constants of DPPs for
ACA substrates increased up to 4.7-fold. Fluorescence-activated droplet
sorting made high-throughput screening of microorganisms based on
DPP activity using the dipeptidyl ACA substrate possible. Since ACA
could be applied to various substrates as a fluorescent probe, detectable
microbial enzyme activities for droplet-based microfluidic systems
can be largely expanded.
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Affiliation(s)
- Akihiro Nakamura
- Department of Science of Technology Innovation, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Nobuyuki Honma
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Yuma Tanaka
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Yoshiyuki Suzuki
- Department of Science of Technology Innovation, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Yosuke Shida
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Yuko Tsuda
- Faculty of Pharmaceutical Sciences, Cooperative Research Center of Life Sciences, Kobe Gakuin University, 1-1-3 Minatojima, Chuo-ku, Kobe, Hyogo 650-8586, Japan
| | - Koushi Hidaka
- Graduate School of Health Sciences, Kobe University, 7-10-2 Tomogaoka, Suma-ku, Kobe, Hyogo 654-0142, Japan
| | - Wataru Ogasawara
- Department of Science of Technology Innovation, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan.,Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
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6
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Payne EM, Holland-Moritz DA, Sun S, Kennedy RT. High-throughput screening by droplet microfluidics: perspective into key challenges and future prospects. LAB ON A CHIP 2020; 20:2247-2262. [PMID: 32500896 DOI: 10.1039/d0lc00347f] [Citation(s) in RCA: 73] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
In two decades of development, impressive strides have been made for automating basic laboratory operations in droplet-based microfluidics, allowing the emergence of a new form of high-throughput screening and experimentation in nanoliter to femtoliter volumes. Despite advancements in droplet storage, manipulation, and analysis, the field has not yet been widely adapted for many high-throughput screening (HTS) applications. Broad adoption and commercial development of these techniques require robust implementation of strategies for the stable storage, chemical containment, generation of libraries, sample tracking, and chemical analysis of these small samples. We discuss these challenges for implementing droplet HTS and highlight key strategies that have begun to address these concerns. Recent advances in the field leave us optimistic about the future prospects of this rapidly developing technology.
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Affiliation(s)
- Emory M Payne
- Department of Chemistry, University of Michigan, Ann Arbor, MI, USA.
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7
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Droplet Microfluidics-Enabled High-Throughput Screening for Protein Engineering. MICROMACHINES 2019; 10:mi10110734. [PMID: 31671786 PMCID: PMC6915371 DOI: 10.3390/mi10110734] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Revised: 10/22/2019] [Accepted: 10/26/2019] [Indexed: 12/19/2022]
Abstract
Protein engineering—the process of developing useful or valuable proteins—has successfully created a wide range of proteins tailored to specific agricultural, industrial, and biomedical applications. Protein engineering may rely on rational techniques informed by structural models, phylogenic information, or computational methods or it may rely upon random techniques such as chemical mutation, DNA shuffling, error prone polymerase chain reaction (PCR), etc. The increasing capabilities of rational protein design coupled to the rapid production of large variant libraries have seriously challenged the capacity of traditional screening and selection techniques. Similarly, random approaches based on directed evolution, which relies on the Darwinian principles of mutation and selection to steer proteins toward desired traits, also requires the screening of very large libraries of mutants to be truly effective. For either rational or random approaches, the highest possible screening throughput facilitates efficient protein engineering strategies. In the last decade, high-throughput screening (HTS) for protein engineering has been leveraging the emerging technologies of droplet microfluidics. Droplet microfluidics, featuring controlled formation and manipulation of nano- to femtoliter droplets of one fluid phase in another, has presented a new paradigm for screening, providing increased throughput, reduced reagent volume, and scalability. We review here the recent droplet microfluidics-based HTS systems developed for protein engineering, particularly directed evolution. The current review can also serve as a tutorial guide for protein engineers and molecular biologists who need a droplet microfluidics-based HTS system for their specific applications but may not have prior knowledge about microfluidics. In the end, several challenges and opportunities are identified to motivate the continued innovation of microfluidics with implications for protein engineering.
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8
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Ong ILH, Amstad E. Selectively Permeable Double Emulsions. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2019; 15:e1903054. [PMID: 31517446 DOI: 10.1002/smll.201903054] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 08/12/2019] [Indexed: 06/10/2023]
Abstract
Natural organisms are made of different types of microcompartments, many of which are enclosed by cell membranes. For these organisms to display a proper function, the microcompartments must be selectively permeable. For example, cell membranes are typically permeable toward small, uncharged molecules such as water, selected nutrients, and cell signaling molecules, but impermeable toward many larger biomolecules. Here, it is reported for the first time dynamic compartments, namely surfactant-stabilized double emulsions, that display selective and tunable permeability. Selective permeability is imparted to double emulsions by stabilizing them with catechol-functionalized surfactants that transport molecules across the oil shell of double emulsions only if they electrostatically or hydrophobically attract encapsulants. These double emulsions are employed as semipermeable picoliter-sized vessels to controllably perform complexation reactions inside picoliter-sized aqueous cores. This thus far unmet level of control over the transport of reagents across oil phases opens up new possibilities to use double emulsion drops as dynamic and selectively permeable microcompartments to initiate and maintain chemical and biochemical reactions in picoliter-sized cell-mimetic compartments.
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Affiliation(s)
- Irvine Lian Hao Ong
- Soft Materials Laboratory, Institute of Materials, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland
| | - Esther Amstad
- Soft Materials Laboratory, Institute of Materials, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland
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9
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Danielson C, Pappas G, Phelps L, Melvin AT, Park K. Static microdroplet array generated by spraying and analyzed with automated microscopy and image processing. Anal Biochem 2019; 587:113452. [PMID: 31563443 DOI: 10.1016/j.ab.2019.113452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 09/05/2019] [Accepted: 09/24/2019] [Indexed: 10/25/2022]
Abstract
Microdroplets have received increasing interest as practical platforms for high-throughput biochemical analysis. Typically, numerous discrete aqueous microdroplets containing biochemical targets are generated in a continuous oil phase and characterized using a flow-through configuration. Although this approach is capable of extremely high throughput, it is challenging to provide dynamic characterization of time-dependent reaction kinetics. In this paper, we present a practical and affordable method to create and analyze a massive array of static aqueous microdroplets immersed in oil for biochemical analysis. The discrete microdroplets were produced by an air-spray gun, imaged by automated microscopy, and then characterized by image processing. The location, area, and fluorescence intensity of randomly generated individual microdroplets were automatically registered for high-throughput characterization. With this approach, we rapidly produced and characterized a static microdroplet array of over 0.7 million microdroplets with an average volume of 300 fL and a mean population density of 1.5*105 microdroplets/cm2. Using the developed setup, we demonstrated the dependency of the microdroplets' fluorescence intensity on their volume, as well as characterized the time-dependent enzyme reaction kinetics of β-galactosidase-mediated cleavage of the substrate fluorescein di-β-d-galactopyranoside (FDG). The new approach described herein provides an inexpensive alternative solution for high-throughput analysis of dynamic biochemical processes.
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Affiliation(s)
- Christian Danielson
- Division of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Gavin Pappas
- Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Lance Phelps
- Division of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Adam T Melvin
- Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Kidong Park
- Division of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA.
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10
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Chiu FWY, Stavrakis S. High-throughput droplet-based microfluidics for directed evolution of enzymes. Electrophoresis 2019; 40:2860-2872. [PMID: 31433062 PMCID: PMC6899980 DOI: 10.1002/elps.201900222] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/10/2019] [Accepted: 08/12/2019] [Indexed: 01/12/2023]
Abstract
Natural enzymes have evolved over millions of years to allow for their effective operation within specific environments. However, it is significant to note that despite their wide structural and chemical diversity, relatively few natural enzymes have been successfully applied to industrial processes. To address this limitation, directed evolution (DE) (a method that mimics the process of natural selection to evolve proteins toward a user‐defined goal) coupled with droplet‐based microfluidics allows the detailed analysis of millions of enzyme variants on ultra‐short timescales, and thus the design of novel enzymes with bespoke properties. In this review, we aim at presenting the development of DE over the last years and highlighting the most important advancements in droplet‐based microfluidics, made in this context towards the high‐throughput demands of enzyme optimization. Specifically, an overview of the range of microfluidic unit operations available for the construction of DE platforms is provided, focusing on their suitability and benefits for cell‐based assays, as in the case of directed evolution experimentations.
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Affiliation(s)
- Flora W Y Chiu
- Institute for Chemical and Bioengineering, ETH Zürich, Zürich, Switzerland
| | - Stavros Stavrakis
- Institute for Chemical and Bioengineering, ETH Zürich, Zürich, Switzerland
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11
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Buryska T, Vasina M, Gielen F, Vanacek P, van Vliet L, Jezek J, Pilat Z, Zemanek P, Damborsky J, Hollfelder F, Prokop Z. Controlled Oil/Water Partitioning of Hydrophobic Substrates Extending the Bioanalytical Applications of Droplet-Based Microfluidics. Anal Chem 2019; 91:10008-10015. [PMID: 31240908 DOI: 10.1021/acs.analchem.9b01839] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Functional annotation of novel proteins lags behind the number of sequences discovered by the next-generation sequencing. The throughput of conventional testing methods is far too low compared to sequencing; thus, experimental alternatives are needed. Microfluidics offer high throughput and reduced sample consumption as a tool to keep up with a sequence-based exploration of protein diversity. The most promising droplet-based systems have a significant limitation: leakage of hydrophobic compounds from water compartments to the carrier prevents their use with hydrophilic reagents. Here, we present a novel approach of substrate delivery into microfluidic droplets and apply it to high-throughput functional characterization of enzymes that convert hydrophobic substrates. Substrate delivery is based on the partitioning of hydrophobic chemicals between the oil and water phases. We applied a controlled distribution of 27 hydrophobic haloalkanes from oil to reaction water droplets to perform substrate specificity screening of eight model enzymes from the haloalkane dehalogenase family. This droplet-on-demand microfluidic system reduces the reaction volume 65 000-times and increases the analysis speed almost 100-fold compared to the classical test tube assay. Additionally, the microfluidic setup enables a convenient analysis of dependences of activity on the temperature in a range of 5 to 90 °C for a set of mesophilic and hyperstable enzyme variants. A high correlation between the microfluidic and test tube data supports the approach robustness. The precision is coupled to a considerable throughput of >20 000 reactions per day and will be especially useful for extending the scope of microfluidic applications for high-throughput analysis of reactions including compounds with limited water solubility.
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Affiliation(s)
- Tomas Buryska
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Faculty of Science , Masaryk University , Kamenice 5 , Brno 625 00 , Czech Republic.,International Clinical Research Center , St. Anne's University Hospital , Pekarska 53 , Brno 656 91 , Czech Republic
| | - Michal Vasina
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Faculty of Science , Masaryk University , Kamenice 5 , Brno 625 00 , Czech Republic.,International Clinical Research Center , St. Anne's University Hospital , Pekarska 53 , Brno 656 91 , Czech Republic
| | - Fabrice Gielen
- Department of Biochemistry , University of Cambridge , 80 Tennis Court Road , Cambridge CB2 1GA , United Kingdom.,Living Systems Institute , University of Exeter , Exeter EX4 4QD , United Kingdom
| | - Pavel Vanacek
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Faculty of Science , Masaryk University , Kamenice 5 , Brno 625 00 , Czech Republic.,International Clinical Research Center , St. Anne's University Hospital , Pekarska 53 , Brno 656 91 , Czech Republic
| | - Liisa van Vliet
- Department of Biochemistry , University of Cambridge , 80 Tennis Court Road , Cambridge CB2 1GA , United Kingdom
| | - Jan Jezek
- Institute of Scientific Instruments, Czech Academy of Sciences , Kralovopolska 147 , Brno 612 64 , Czech Republic
| | - Zdenek Pilat
- Institute of Scientific Instruments, Czech Academy of Sciences , Kralovopolska 147 , Brno 612 64 , Czech Republic
| | - Pavel Zemanek
- Institute of Scientific Instruments, Czech Academy of Sciences , Kralovopolska 147 , Brno 612 64 , Czech Republic
| | - Jiri Damborsky
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Faculty of Science , Masaryk University , Kamenice 5 , Brno 625 00 , Czech Republic.,International Clinical Research Center , St. Anne's University Hospital , Pekarska 53 , Brno 656 91 , Czech Republic
| | - Florian Hollfelder
- Department of Biochemistry , University of Cambridge , 80 Tennis Court Road , Cambridge CB2 1GA , United Kingdom
| | - Zbynek Prokop
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Faculty of Science , Masaryk University , Kamenice 5 , Brno 625 00 , Czech Republic.,International Clinical Research Center , St. Anne's University Hospital , Pekarska 53 , Brno 656 91 , Czech Republic
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12
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Etienne G, Vian A, Biočanin M, Deplancke B, Amstad E. Cross-talk between emulsion drops: how are hydrophilic reagents transported across oil phases? LAB ON A CHIP 2018; 18:3903-3912. [PMID: 30465575 DOI: 10.1039/c8lc01000e] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Emulsion drops are frequently used as vessels, for example, to conduct biochemical reactions in small volumes or to perform screening assays at high throughputs while consuming minimal sample volumes. These applications typically require drops that do not allow exchange of reagents such that no cross-contamination occurs. Unfortunately, in many cases, reagents are exchanged between emulsion drops even if they have a low solubility in the surrounding phase, resulting in cross-contaminations. Here, we investigate the mechanism by which hydrophilic reagents are transported across an oil phase using water-oil-water double emulsion drops as a model system. Remarkably, even large objects, including 11 000 base pair double-stranded circular DNA are transported across oil shells. Importantly, this reagent transport, that is to a large extent caused by aqueous drops that spontaneously form at the water-oil interface, is not limited to double emulsions but also occurs between single emulsion drops. We demonstrate that the uncontrolled reagent transport can be decreased by at least an order of magnitude if appropriate surfactants that lower the interfacial tension only moderately are employed or if the shell thickness of double emulsions is decreased to a few hundreds of nanometers.
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Affiliation(s)
- Gianluca Etienne
- Soft Materials Laboratory, Institute of Materials, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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13
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Nightingale AM, Hassan SU, Evans GWH, Coleman SM, Niu X. Nitrate measurement in droplet flow: gas-mediated crosstalk and correction. LAB ON A CHIP 2018; 18:1903-1913. [PMID: 29877549 DOI: 10.1039/c8lc00092a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
In droplet microfluidics, droplets have traditionally been considered discrete self-contained reaction chambers, however recent work has shown that dissolved solutes can transfer into the oil phase and migrate into neighbouring droplets under certain conditions. The majority of reports on such inter-droplet "crosstalk" have focused on surfactant-driven mechanisms, such as transport within micelles. While trialling a droplet-based system for quantifying nitrate in water, we encountered crosstalk driven by a very different mechanism: conversion of the analyte to a gaseous intermediate which subsequently diffused between droplets. Importantly we found that the crosstalk occurred predictably, could be experimentally quantified, and measurements rationally post-corrected. This showed that droplet microfluidic systems susceptible to crosstalk such as this can nonetheless be used for quantitative analysis.
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Affiliation(s)
- Adrian M Nightingale
- Faculty of Engineering and the Environment, University of Southampton, Southampton, SO17 1BJ, UK.
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14
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Cochrane WG, Hackler AL, Cavett VJ, Price AK, Paegel BM. Integrated, Continuous Emulsion Creamer. Anal Chem 2017; 89:13227-13234. [PMID: 29124927 DOI: 10.1021/acs.analchem.7b03070] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Automated and reproducible sample handling is a key requirement for high-throughput compound screening and currently demands heavy reliance on expensive robotics in screening centers. Integrated droplet microfluidic screening processors are poised to replace robotic automation by miniaturizing biochemical reactions to the droplet scale. These processors must generate, incubate, and sort droplets for continuous droplet screening, passively handling millions of droplets with complete uniformity, especially during the key step of sample incubation. Here, we disclose an integrated microfluidic emulsion creamer that packs ("creams") assay droplets by draining away excess oil through microfabricated drain channels. The drained oil coflows with creamed emulsion and then reintroduces the oil to disperse the droplets at the circuit terminus for analysis. Creamed emulsion assay incubation time dispersion was 1.7%, 3-fold less than other reported incubators. The integrated, continuous emulsion creamer (ICEcreamer) was used to miniaturize and optimize measurements of various enzymatic activities (phosphodiesterase, kinase, bacterial translation) under multiple- and single-turnover conditions. Combining the ICEcreamer with current integrated microfluidic DNA-encoded library bead processors eliminates potentially cumbersome instrumentation engineering challenges and is compatible with assays of diverse target class activities commonly investigated in drug discovery.
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Affiliation(s)
- Wesley G Cochrane
- Doctoral Program in the Chemical and Biological Sciences and ‡Department of Chemistry, The Scripps Research Institute , 130 Scripps Way, Jupiter, Florida 33458, United States
| | - Amber L Hackler
- Doctoral Program in the Chemical and Biological Sciences and ‡Department of Chemistry, The Scripps Research Institute , 130 Scripps Way, Jupiter, Florida 33458, United States
| | - Valerie J Cavett
- Doctoral Program in the Chemical and Biological Sciences and ‡Department of Chemistry, The Scripps Research Institute , 130 Scripps Way, Jupiter, Florida 33458, United States
| | - Alexander K Price
- Doctoral Program in the Chemical and Biological Sciences and ‡Department of Chemistry, The Scripps Research Institute , 130 Scripps Way, Jupiter, Florida 33458, United States
| | - Brian M Paegel
- Doctoral Program in the Chemical and Biological Sciences and ‡Department of Chemistry, The Scripps Research Institute , 130 Scripps Way, Jupiter, Florida 33458, United States
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15
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Autour A, Ryckelynck M. Ultrahigh-Throughput Improvement and Discovery of Enzymes Using Droplet-Based Microfluidic Screening. MICROMACHINES 2017. [PMCID: PMC6189954 DOI: 10.3390/mi8040128] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Enzymes are extremely valuable tools for industrial, environmental, and biotechnological applications and there is a constant need for improving existing biological catalysts and for discovering new ones. Screening microbe or gene libraries is an efficient way of identifying new enzymes. In this view, droplet-based microfluidics appears to be one of the most powerful approaches as it allows inexpensive screenings in well-controlled conditions and an ultrahigh-throughput regime. This review aims to introduce the main microfluidic devices and concepts to be considered for such screening before presenting and discussing the latest successful applications of the technology for enzyme discovery.
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16
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Kim M, Leong CM, Pan M, Blauch LR, Tang SKY. High-Efficiency and High-Throughput On-Chip Exchange of the Continuous Phase in Droplet Microfluidic Systems. SLAS Technol 2017; 22:529-535. [PMID: 28402212 DOI: 10.1177/2472630317692558] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
This article describes an integrated platform for the on-chip exchange of the continuous phase in droplet microfluidic systems. The drops used in this work are stabilized by amphiphilic nanoparticles. For some characterizations and applications of these nanoparticle-stabilized drops, including the measurement of adsorption dynamics of nanoparticles to the droplet surface, it is necessary to change the composition of the continuous phase from that used during the droplet generation process. Thus far, no work has reported the exchange of the continuous phase for a large number (>1 million) of drops in a microfluidic system. This article describes the design and characterization of a high-efficiency and high-throughput on-chip exchanger of the continuous phase in a continuous-flow droplet microfluidic system. The efficiency of exchange was higher than 97%. The throughput was greater than 1 million drops/min, and this can be increased further by increasing the number of parallel exchangers used. Because drops are injected into the exchanger in a continuous-flow manner, the method is directly compatible with automation to further increase its reliability and potential scale-up.
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Affiliation(s)
- Minkyu Kim
- 1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Chia Min Leong
- 1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Ming Pan
- 2 Department of Material Science and Engineering, Stanford University, Stanford, CA, USA
| | - Lucas R Blauch
- 1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Sindy K Y Tang
- 1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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17
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Yelleswarapu VR, Jeong HH, Yadavali S, Issadore D. Ultra-high throughput detection (1 million droplets per second) of fluorescent droplets using a cell phone camera and time domain encoded optofluidics. LAB ON A CHIP 2017; 17:1083-1094. [PMID: 28225099 DOI: 10.1039/c6lc01489e] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Droplet-based assays-in which ultra-sensitive molecular measurements are made by performing millions of parallel experiments in picoliter droplets-have generated enormous enthusiasm due to their single molecule resolution and robustness to reaction conditions. These assays have great untapped potential for point of care diagnostics but are currently confined to laboratory settings due to the instrumentation necessary to serially generate, control, and measure tens of millions of droplets. To address this challenge, we have developed the microdroplet megascale detector (μMD) that can generate and detect the fluorescence of millions of droplets per second (1000× faster than conventional approaches) using only a conventional cell phone camera. The key innovation of our approach is borrowed from the telecommunications industry, wherein we modulate the excitation light with a pseudorandom sequence that enables individual droplets to be resolved that would otherwise overlap due to the limited frame rate of digital cameras. Using this approach, the μMD measures droplets at a rate of 106 droplets per sec (ϕ = 166 mL h-1) in 120 parallel microfluidic channels and achieves a limit of detection LOD = 1 μM Rhodamine dye, sufficient for typical droplet based assays. We incorporate this new droplet detection technology with our previously reported parallelized droplet production strategy, incorporating 200 parallel droplet makers and only one set of continuous and droplet phase inputs and one output line. By miniaturizing and integrating droplet based diagnostics into a handheld format, the μMD platform can translate ultra-sensitive droplet based assays into a self-contained platform for practical use in clinical and industrial settings.
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Affiliation(s)
- Venkata R Yelleswarapu
- Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
| | - Heon-Ho Jeong
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Sagar Yadavali
- Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
| | - David Issadore
- Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA. and Department of Electrical and Systems Engineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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18
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Chan CL, Bolognesi G, Bhandarkar A, Friddin MS, Brooks NJ, Seddon JM, Law RV, Barter LMC, Ces O. DROPLAY: laser writing of functional patterns within biological microdroplet displays. LAB ON A CHIP 2016; 16:4621-4627. [PMID: 27797387 DOI: 10.1039/c6lc01219a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In this study, we introduce an optofluidic method for the rapid construction of large-area cell-sized droplet assemblies with user-defined, re-writable, two-dimensional patterns of functional droplets. Light responsive water-in-oil droplets capable of releasing fluorescent dye molecules upon exposure were generated and self-assembled into arrays inside a microfluidic device. This biological architecture was exploited by the scanning laser of a confocal microscope to 'write' user defined patterns of differentiated (fluorescent) droplets in a network of originally undifferentiated (non-fluorescent) droplets. As a result, long lasting images were produced on a droplet fabric with droplets acting as pixels of a biological monitor, which can be erased and re-written on-demand. Regio-specific light-induced droplet differentiation within a large population of droplets provides a new paradigm for the rapid construction of bio-synthetic systems with potential as tissue mimics and biological display materials.
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Affiliation(s)
- Chi Long Chan
- Department of Chemistry, Imperial College London, London, UK.
| | - Guido Bolognesi
- Department of Chemistry, Imperial College London, London, UK.
| | - Archis Bhandarkar
- Department of Biological Engineering, Massachusetts Institute of Technology, USA
| | - Mark S Friddin
- Department of Chemistry, Imperial College London, London, UK.
| | | | - John M Seddon
- Department of Chemistry, Imperial College London, London, UK.
| | - Robert V Law
- Department of Chemistry, Imperial College London, London, UK.
| | | | - Oscar Ces
- Department of Chemistry, Imperial College London, London, UK.
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19
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Abstract
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 [Formula: see text] 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.
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20
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Kaminski TS, Scheler O, Garstecki P. Droplet microfluidics for microbiology: techniques, applications and challenges. LAB ON A CHIP 2016; 16:2168-87. [PMID: 27212581 DOI: 10.1039/c6lc00367b] [Citation(s) in RCA: 239] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Droplet microfluidics has rapidly emerged as one of the key technologies opening up new experimental possibilities in microbiology. The ability to generate, manipulate and monitor droplets carrying single cells or small populations of bacteria in a highly parallel and high throughput manner creates new approaches for solving problems in diagnostics and for research on bacterial evolution. This review presents applications of droplet microfluidics in various fields of microbiology: i) detection and identification of pathogens, ii) antibiotic susceptibility testing, iii) studies of microbial physiology and iv) biotechnological selection and improvement of strains. We also list the challenges in the dynamically developing field and new potential uses of droplets in microbiology.
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Affiliation(s)
- Tomasz S Kaminski
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
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21
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Scheler O, Kaminski TS, Ruszczak A, Garstecki P. Dodecylresorufin (C12R) Outperforms Resorufin in Microdroplet Bacterial Assays. ACS APPLIED MATERIALS & INTERFACES 2016; 8:11318-11325. [PMID: 27100211 DOI: 10.1021/acsami.6b02360] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This paper proves that dodecylresorufin (C12R) outperforms resorufin (the conventional form of this dye) in droplet microfluidic bacterial assays. Resorufin is a marker dye that is widely used in different fields of microbiology and has increasingly been applied in droplet microfluidic assays and experiments. The main concern associated with resorufin in droplet-based systems is dye leakage into the oil phase and neighboring droplets. The leakage decreases the performance of assays because it causes averaging of the signal between the positive (bacteria-containing) and negative (empty) droplets. Here we show that C12R is a promising alternative to conventional resorufin because it maintains higher sensitivity, specificity, and signal-to-noise ratio over time. These characteristics make C12R a suitable reagent for droplet digital assays and for monitoring of microbial growth in droplets.
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Affiliation(s)
- Ott Scheler
- Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland
- Institute of Molecular and Cell Biology, University of Tartu , Riia 23, 51010 Tartu, Estonia
| | - Tomasz S Kaminski
- Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Artur Ruszczak
- Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Piotr Garstecki
- Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland
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22
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Controlling molecular transport in minimal emulsions. Nat Commun 2016; 7:10392. [PMID: 26797564 PMCID: PMC4735829 DOI: 10.1038/ncomms10392] [Citation(s) in RCA: 142] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 12/08/2015] [Indexed: 12/24/2022] Open
Abstract
Emulsions are metastable dispersions in which molecular transport is a major mechanism driving the system towards its state of minimal energy. Determining the underlying mechanisms of molecular transport between droplets is challenging due to the complexity of a typical emulsion system. Here we introduce the concept of ‘minimal emulsions', which are controlled emulsions produced using microfluidic tools, simplifying an emulsion down to its minimal set of relevant parameters. We use these minimal emulsions to unravel the fundamentals of transport of small organic molecules in water-in-fluorinated-oil emulsions, a system of great interest for biotechnological applications. Our results are of practical relevance to guarantee a sustainable compartmentalization of compounds in droplet microreactors and to design new strategies for the dynamic control of droplet compositions. Emulsion droplets have many biotechnological applications, such as parallelized single cell analysis. Here, Gruner et al. introduce the concept of the minimal emulsions in a microfluidic device that allows full control of molecular transport between emulsion droplets.
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23
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Affiliation(s)
- Alexander K. Price
- Department of Chemistry, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Brian M. Paegel
- Department of Chemistry, The Scripps Research Institute, Jupiter, FL 33458, United States
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24
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Pan M, Kim M, Blauch L, Tang SKY. Surface-functionalizable amphiphilic nanoparticles for pickering emulsions with designer fluid–fluid interfaces. RSC Adv 2016. [DOI: 10.1039/c6ra03950b] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
This work describes the synthesis of amphiphilic silica nanoparticles with functionalizable surfaces for stabilizing aqueous drops in fluorinated oils, and for enabling the generation of emulsions with tailored interfacial properties.
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Affiliation(s)
- Ming Pan
- Department of Materials Science and Engineering
- Stanford University
- Stanford
- USA
| | - Minkyu Kim
- Department of Mechanical Engineering
- Stanford University
- Stanford
- USA
| | - Lucas Blauch
- Department of Mechanical Engineering
- Stanford University
- Stanford
- USA
| | - Sindy K. Y. Tang
- Department of Mechanical Engineering
- Stanford University
- Stanford
- USA
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25
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Pan M, Lyu F, Tang SKY. Fluorinated Pickering Emulsions with Nonadsorbing Interfaces for Droplet-based Enzymatic Assays. Anal Chem 2015; 87:7938-43. [DOI: 10.1021/acs.analchem.5b01753] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Ming Pan
- Department
of Material Science and Engineering, Stanford University, Stanford, California 94305-2004, United States
| | - Fengjiao Lyu
- Department
of Mechanical Engineering, Stanford University, Stanford, California 94305-2004, United States
| | - Sindy K. Y. Tang
- Department
of Mechanical Engineering, Stanford University, Stanford, California 94305-2004, United States
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26
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Gruner P, Riechers B, Chacòn Orellana LA, Brosseau Q, Maes F, Beneyton T, Pekin D, Baret JC. Stabilisers for water-in-fluorinated-oil dispersions: Key properties for microfluidic applications. Curr Opin Colloid Interface Sci 2015. [DOI: 10.1016/j.cocis.2015.07.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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27
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Pan M, Rosenfeld L, Kim M, Xu M, Lin E, Derda R, Tang SKY. Fluorinated pickering emulsions impede interfacial transport and form rigid interface for the growth of anchorage-dependent cells. ACS APPLIED MATERIALS & INTERFACES 2014; 6:21446-53. [PMID: 25347285 DOI: 10.1021/am506443e] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
This study describes the design and synthesis of amphiphilic silica nanoparticles for the stabilization of aqueous drops in fluorinated oils for applications in droplet microfluidics. The success of droplet microfluidics has thus far relied on one type of surfactant for the stabilization of drops. However, surfactants are known to have two key limitations: (1) interdrop molecular transport leads to cross-contamination of droplet contents, and (2) the incompatibility with the growth of adherent mammalian cells as the liquid-liquid interface is too soft for cell adhesion. The use of nanoparticles as emulsifiers overcomes these two limitations. Particles are effective in mitigating undesirable interdrop molecular transport as they are irreversibly adsorbed to the liquid-liquid interface. They do not form micelles as surfactants do, and thus, a major pathway for interdrop transport is eliminated. In addition, particles at the droplet interface provide a rigid solid-like interface to which cells could adhere and spread, and are thus compatible with the proliferation of adherent mammalian cells such as fibroblasts and breast cancer cells. The particles described in this work can enable new applications for high-fidelity assays and for the culture of anchorage-dependent cells in droplet microfluidics, and they have the potential to become a competitive alternative to current surfactant systems for the stabilization of drops critical for the success of the technology.
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Affiliation(s)
- Ming Pan
- Department of Material Science and Engineering, Stanford University , Stanford, California 94305-2004, United States
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