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Cyclic Olefin Copolymer Plasma millireactors
Laboratoire Procédés - Plasmas - Microsystèmes - Schelcher G, Guyon C, Ognier S, Cavadias S, Martinez E, Taniga V, Malaquin L, Tabeling P and Tatoulian M
Lab. Chip - 14(16) 3037-42 - DOI: 10.1039/c4lc00423j - 2013
The novelty of this paper lies in the development of a multistep process for the manufacturing of plasma millireactors operating at atmospheric pressure. The fabrication process relies on the integration of metallic electrodes over a cyclic olefin copolymer chip by a combination of photopatterning and sputtering. The developed plasma millireactors were successfully tested by creating air discharges in the gas volume of the millichannel. A sputtered silica layer was deposited on the channel walls to provide a barrier between the plasma and the polymer in order to prevent the alteration of polymer surfaces during the plasma treatment. Interest in this process of employing plasma millireactor as a high reactive environment is demonstrated here by the degradation of a volatile organic compound (acetaldehyde) in ambient air. In this miniaturized device, we obtained a high acetaldehyde conversion (98%) for a specific input energy lower than 200 J L(-1).
Abnormal recruitment of extracellular matrix proteins by excess Notch3ECD: a new pathomechanism in CADASIL
Laboratoire Spectrométrie de masse biologique et protéomique - Monet-Leprêtre M, Haddad I, Baron-Menguy C, Fouillot-Panchal M, Riani M, Domenga-Denier V, Dussaule C, Cognat E, Vinh J and Joutel A
Brain Oxford - (Pt 6) 1830-45 - DOI: 10.1093/brain/awt092 - 2013
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, or CADASIL, one of the most common inherited small vessel diseases of the brain, is characterized by a progressive loss of vascular smooth muscle cells and extracellular matrix accumulation. The disease is caused by highly stereotyped mutations within the extracellular domain of the NOTCH3 receptor (Notch3(ECD)) that result in an odd number of cysteine residues. While CADASIL-associated NOTCH3 mutations differentially affect NOTCH3 receptor function and activity, they all are associated with early accumulation of Notch3(ECD)-containing aggregates in small vessels. We still lack mechanistic explanation to link NOTCH3 mutations with small vessel pathology. Herein, we hypothesized that excess Notch3(ECD) could recruit and sequester functionally important proteins within small vessels of the brain. We performed biochemical, nano-liquid chromatography-tandem mass spectrometry and immunohistochemical analyses, using cerebral and arterial tissue derived from patients with CADASIL and mouse models of CADASIL that exhibit vascular lesions in the end- and early-stage of the disease, respectively. Biochemical fractionation of brain and artery samples demonstrated that mutant Notch3(ECD) accumulates in disulphide cross-linked detergent-insoluble aggregates in mice and patients with CADASIL. Further proteomic and immunohistochemical analyses identified two functionally important extracellular matrix proteins, tissue inhibitor of metalloproteinases 3 (TIMP3) and vitronectin (VTN) that are sequestered into Notch3(ECD)-containing aggregates. Using cultured cells, we show that increased levels or aggregation of Notch3 enhances the formation of Notch3(ECD)-TIMP3 complex, promoting TIMP3 recruitment and accumulation. In turn, TIMP3 promotes complex formation including NOTCH3 and VTN. In vivo, brain vessels from mice and patients with CADASIL exhibit elevated levels of both insoluble cross-linked and soluble TIMP3 species. Moreover, reverse zymography assays show a significant elevation of TIMP3 activity in the brain vessels from mice and patients with CADASIL. Collectively, our findings lend support to a Notch3(ECD) cascade hypothesis in CADASIL disease pathology, which posits that aggregation/accumulation of Notch3(ECD) in the brain vessels is a central event, promoting the abnormal recruitment of functionally important extracellular matrix proteins that may ultimately cause multifactorial toxicity. Specifically, our results suggest a dysregulation of TIMP3 activity, which could contribute to mutant Notch3(ECD) toxicity by impairing extracellular matrix homeostasis in small vessels.
Landscape of protein–protein interactions in Drosophila immune deficiency signaling during bacterial challenge
Laboratoire Spectrométrie de masse biologique et protéomique - Hidehiro Fukuyamaa, Yann Verdierb, Yongsheng Guana, Chieko Makino-Okamuraa, Victoria Shilovaa, Xi Liua, E. Maksouda, J. Matsubayashia, I. Haddadb, K. Spirohne, K. Onof, C. Hetruc, J. Rossierb, Trey Idekerf, M. Boutrose, Joëlle Vinh and Jules A. Hoffmann
Proc. Nat. Acad. Sci. USA - vol.110(n°26) 10717–22 - DOI: 10.1073/pnas.1304380110 - 2013
The Drosophila defense against pathogens largely relies on the activation of two signaling pathways: immune deficiency (IMD) and Toll. The IMD pathway is triggered mainly by Gram-negative bacteria, whereas the Toll pathway responds predominantly to Gram-positive bacteria and fungi. The activation of these pathways leads to the rapid induction of numerous NF-κB–induced immune response genes, including antimicrobial peptide genes. The IMD pathway shows significant similarities with the TNF receptor pathway. Recent evidence indicates that the IMD pathway is also activated in response to various noninfectious stimuli (i.e., inflammatory-like reactions). To gain a better understanding of the molecular machinery underlying the pleiotropic functions of this pathway, we first performed a comprehensive proteomics analysis to identify the proteins interacting with the 11 canonical members of the pathway initially identified by genetic studies. We identified 369 interacting proteins (corresponding to 291 genes) in heat-killed Escherichia coli-stimulated Drosophila S2 cells, 92% of which have human orthologs. A comparative analysis of gene ontology from fly or human gene annotation databases points to four significant common categories: (i) the NuA4, nucleosome acetyltransferase of H4, histone acetyltransferase complex, (ii) the switching defective/sucrose nonfermenting-type chromatin remodeling complex, (iii) transcription coactivator activity, and (iv) translation factor activity. Here we demonstrate that sumoylation of the IκB kinase homolog immune response-deficient 5 plays an important role in the induction of antimicrobial peptide genes through a highly conserved sumoylation consensus site during bacterial challenge. Taken together, the proteomics data presented here provide a unique avenue for a comparative functional analysis of proteins involved in innate immune reactions in flies and mammals.
Binding parameters between an aptamer and its target by frontal analysis continuous microchip electrophoresis (FACMCE): a comprehensive study of buffer composition and thermal treatment in the case of lysozyme
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - M. Girardot, H-Y. Li, S. Descroix, A. Varenne
Chromatographia - 76 305-312 - DOI: 10.1007/s10337-012-2346-x - 2013
An original and simple methodology based on microchip electrophoresis (MCE) in a continuous frontal analysis mode (named frontal analysis continuous microchip electrophoresis, FACMCE) was developed for the simultaneous determination of the binding parameters, i.e. ligand-site dissociation constant (k(d)) and number of binding sites on the substrate (n). This simultaneous determination was exemplified with the interaction between an aptamer and its target. The selected target is a strongly basic protein, lysozyme, as its quantification is of great interest due to its antimicrobial and allergenic properties. A glass microdevice equipped with a fluorescence detection system was coated with hydroxypropylcellulose, reducing the electroosmotic flow and adsorption onto the channel walls. This microdevice allowed the continuous electrokinetic injection of a mixture of fluorescently labelled aptamer and non-labelled lysozyme. By determining the concentration of the free fluorescently labelled aptamer thanks to its corresponding plateau height, mathematical linearization methods allowed to determine a k(d) value of 48.4±8.0 nM, consistent with reported results (31 nM), while the average number of binding sites n on lysozyme, never determined before, was 0.16±0.03. These results seem to indicate that the buffer nature and the SELEX process should influence the number and affinity of the binding sites. In parallel it has been shown that the binding between lysozyme and its aptamer presents two sites of different binding affinities.
Aptamer-conjugated nanoparticles: Preservation of targeting functionality demonstrated by microchip electrophoresis in frontal mode
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - M. Girardot, F. d'Orlye, S. Descroix, A. Varenne.
Analytical Biochemistry - 435 150-152 - PMID:23333271 - 2013
Aptamer-conjugated nanoparticles (Apt-NPs) are increasingly being developed for biomedical purposes and especially for diagnosis and therapy. However, there is no quantitative study of the targeting functionality of such grafted aptamers compared with free aptamers. Thus, we report the first determination of binding parameters for Apt-NP/target complexes, thanks to a continuous frontal analysis in a microchip electrophoresis format (named FACMCE), based on a methodology previously developed by our group. As a model system, the targeting ability of a lysozyme-binding aptamer conjugated to fluorescent maghemite nanoparticles was evaluated and showed evidence that the conjugation does not alter the affinity of this aptamer.
Electrokinetic characterization of superparamagnetic nanoparticle–aptamer conjugates: design of new highly specific probes for miniaturized molecular diagnostics
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - M. Girardot, F. d'Orlye, A. Varenne
Anal. Bioanal. Chem - 406(4) :1089-98 - DOI:10.1007/s00216-013-7265-7 - 2013
With the view of designing new nanoparticle (NP)-aptamer conjugates and proving their suitability as biorecognition tools for miniaturized molecular diagnostics, new maghemite-silica core-shell NP-aptamer conjugates were characterized for the first time in terms of grafting rate and colloidal stability under electrophoretic conditions using capillary electrophoresis. After the grafting rate (on the order of six to 50) of the lysozyme-binding aptamer had been estimated, the electrophoretic stability and peak dispersion of the resulting oligonucleotide-NP conjugates were estimated so as to determine the optimal separation conditions in terms of buffer pH, ionic strength and nature, as well as temperature and electric field strength. The effective surface charge density of the NPs was close to zero for pH lower than 5, which led to some aggregation. The NPs were stable in the pH range from 5 to 9, and an increase in electrophoretic mobility was evidenced with increasing pH. Colloidal stability was preserved at physiological pH for both non-grafted NPs and grafted NPs in the 10-100 mM ionic strength range and in the 15-60 °C temperature range. A strong influence of the nature of the buffer counterion on NP electrophoretic mobility and peak dispersion was evidenced, thus indicating some interactions between buffer components and NP-aptamer conjugates. Whereas an electric field effect (50-900 V cm(-1)) on NP electrophoretic mobility was evidenced, probably linked to counterion dissociation, temperature seems to have an appreciable effect on the zeta potential and aptamer configuration as well. This information is crucial for estimating the potentialities of such biorecognition tools in electrophoretic systems.
Red blood celles decorated with functionalized core-shell magnetic nanoparticles : elucidation of the adsorption mechanism
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - T. D. Mai, F. D’Orlyé, C. Menager, A. Varenne, M. Siaugue
Chem. Comm. - 49(47) :5393-5 - DOI:10.1039/c3cc41513a. - 2013
The decoration of red blood cells (RBCs) with aminated and carboxylated core-shell magnetic nanoparticles (CSMNs) was studied and elucidated. It was demonstrated that only aminated CSMNs could decorate the RBCs and their adsorption interaction is mainly ruled by electrostatic attraction between the positively charged amino groups on CSMNs and the abundant sialic acid groups on the outer surface of RBCs.
Surface functionalization of COC microfluidic materials by plasma and click chemistry processes
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - Y. Ladner, F. D’orlye, C. Perrard, B. Da Silva, C. Guyon, M. Tatoulian, S. Griveau, F. Bedioui & A. Varenne
Plasma Process - 10(11) :959-69 - DOI:10.1002/ppap.201300066 - 2013
A robust method for COC surfaces functionalization was developed for the first time by plasma polymerization. 1-bromopropane in the vapor phase allowed the formation of a brominated deposit on COC surfaces, which stability, homogeneity and chemical nature were evaluated for different experimental conditions. The analysis of vapor phase was achieved by mass spectrometry to control brominated precursor fragmentation. Following nucleophilic exchange in the presence of NaN3 to convert the brominated surface to azide-bearing surface, these modified COC were further functionalized with a fluorescent alkyne, via the copper-catalyzed azide–alkyne cycloaddition reaction, i.e. “click” reaction. Surface modifications were characterized by water contact angle measurement, ellipsometry, electrochemical microscopy, XPS, IR and fluorescence microscopy. This new process was proved to be efficient and stable in time up to 7 days.
Horseradish peroxidase nanopatterned electrodes by click chemistry: Application to the electrochemical detection of paracetamol
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - D. Quinton, A. Maringa, S. Griveau, T. Nyokong & F. Bedioui
Electrochemistry Communications - 31 :112-5 - https://doi.org/10.1002/elan.201300030 - 2013
Electrochemical DNA-biosensors : two-electrode set up well adapted for miniaturized devices
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - M. Lazerges, V. T. Tal, P. Bigey, D. Scherman & F. Bedioui
Sensors & Actuators - B 182 :510-513 - DOI:10.1016/j.snb.2013.02.098 - 2013
The proof of concept of a DNA-biosensor based on a two-electrode electrochemical setup and using a microelectrode as working electrode, well adapted for detection in microliter samples and miniaturization, is presented herein. A 23-base DNA-probe self-assembled monolayer was first formed onto a 50 μm-diameter gold surface. The microelectrode extremity was then immersed in a 50 μL DNA-target solution drop itself deposited onto a 2 mm-diameter gold counter electrode. Transduction occurs via long-range electron transfer, which is enhanced subsequently to hybridization, due to DNA-base π-stacking. Single mismatch detection of this first prototype was matched at room temperature in the nanomolar range without any optimization.
Red blood cells decorated with functionalized core–shell magnetic nanoparticles: elucidation of the adsorption mechanism
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - Thanh Duc Mai, Fanny d’Orlye, Christine Ménager, Anne Varenne and Jean-Michel Siaugue
Chem. Comm. - -49 5393—95 - DOI: 10.1039/C3CC41513A - 2013
High-resolution dose-response screening using droplet-based microfluidics
Laboratoire Biochimie - O.J. Miller, A.E. Harrak, T. Mangeat, J.-C. Baret, L. Frenz, B. El Debs, E. Mayot, M.L. Samuels, E.K. Rooney, P. Dieu, M. Galvan, D.R. Link and A.D. Griffiths
Proc. Nat. Acad. Sci. USA - 109(2) :378–83 - DOI:10.1073/pnas.1113324109 - 2012
A critical early step in drug discovery is the screening of a chemical library. Typically, promising compounds are identified in a primary screen and then more fully characterized in a dose–response analysis with 7–10 data points per compound. Here, we describe a robust microfluidic approach that increases the number of data points to approximately 10,000 per compound. The system exploits Taylor–Aris dispersion to create concentration gradients, which are then segmented into picoliter microreactors by droplet-based microfluidics. The large number of data points results in IC50 values that are highly precise (± 2.40% at 95% confidence) and highly reproducible (CV = 2.45%, n = 16). In addition, the high resolution of the data reveals complex dose–response relationships unambiguously. We used this system to screen a chemical library of 704 compounds against protein tyrosine phosphatase 1B, a diabetes, obesity, and cancer target. We identified a number of novel inhibitors, the most potent being sodium cefsulodine, which has an IC50 of 27 ± 0.83 μM.
A completely in vitro ultrahigh-throughput droplet-based microfluidic screening system for protein engineering and directed evolution
Laboratoire Biochimie - Fallah-Araghi, J.-C. Baret, M. Ryckelynck, and A.D. Griffiths
Lab. Chip - 12(5) :882–91 - DOI: 10.1039/c2lc21035e - 2012
In vitro screening systems based on the coupled transcription and translation of genes using cell-free systems have a number of attractive features for protein engineering and directed evolution. We present a completely in vitro ultrahigh-throughput screening platform using droplet-based microfluidics. Single genes are compartmentalized in aqueous droplets, dispersed in inert carrier oil, and amplified using the polymerase chain reaction (PCR). After amplification, the droplets, now containing 30,000 copies of each gene, are fused one-to-one with droplets containing a cell-free coupled transcription-translation (IVTT) system and the reagents for a fluorogenic assay. Fluorescence-activated electrocoalescence with an aqueous stream is then used to selectively recover genes from droplets containing the desired activity. We demonstrate, by selecting mixtures of lacZ genes encoding the enzyme β-galactosidase and lacZmut genes encoding an inactive variant, that this system can sort at 2000 droplets s(-1): lacZ genes were enriched 502-fold from a 1 : 100 molar ratio of lacZ : lacZmut genes. Indeed, the false positive and false negative error rates were both <0.004 and the results indicate that enrichment is not limited by the sorting efficiency, but by the co-encapsulation of multiple genes in droplets, which is described by the Poisson distribution. Compared to screening using microtiter plate-based systems, the volume and cost of PCR and IVTT reagents are reduced by almost 10(5)-fold, allowing the screening of 10(6) genes using only 150 μL of reagents.
Functional single-cell hybridoma screening using droplet-based microfluidics
Laboratoire Biochimie - B. El Debs, R. Utharala, I.V. Balyasnikova, A.D. Griffiths and C.A. Merten
Proc. Nat. Acad. Sci. USA - 109(29) :11570-5 - DOI: 10.1073/pnas.1204514109 - 2012
Monoclonal antibodies can specifically bind or even inhibit drug targets and have hence become the fastest growing class of human therapeutics. Although they can be screened for binding affinities at very high throughput using systems such as phage display, screening for functional properties (e.g., the inhibition of a drug target) is much more challenging. Typically these screens require the generation of immortalized hybridoma cells, as well as clonal expansion in microtiter plates over several weeks, and the number of clones that can be assayed is typically no more than a few thousand. We present here a microfluidic platform allowing the functional screening of up to 300,000 individual hybridoma cell clones within less than a day. This approach should also be applicable to nonimmortalized primary B-cells, as no cell proliferation is required: Individual cells are encapsulated into aqueous microdroplets and assayed directly for the release of antibodies inhibiting a drug target based on fluorescence. We used this system to perform a model screen for antibodies that inhibit angiotensin converting enzyme 1, a target for hypertension and congestive heart failure drugs. When cells expressing these antibodies were spiked into an unrelated hybridoma cell population in a ratio of 1:10,000 we observed a 9,400-fold enrichment after fluorescence activated droplet sorting. A wide variance in antibody expression levels at the single-cell level within a single hybridoma line was observed and high expressors could be successfully sorted and recultivated.
Fine control of nuclear confinement identifies a threshold deformation leading to lamina rupture and induction of specific genes
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Berre M, Aubertin J, Piel M
Integr Biol (Camb) - 4(11) :1406-14 - DOI:10.1039/c2ib20056b - 2012
The quest to understand how the mechanical and geometrical environment of cells impacts their behavior and fate has been a major force driving the recent development of new technologies in cell biology research. Despite rapid advances in this field, many challenges remain in order to bridge the gap between the classical and simple cell culture plate and the biological reality of actual tissue. In tissues, cells have their physical space constrained by neighboring cells and the extracellular matrix. Here, we propose a simple and versatile device to precisely and dynamically control this confinement parameter in cultured cells. We show that there is a precise threshold deformation above which the nuclear lamina breaks and reconstructs, whereas nuclear volume changes. We also show that different nuclear deformations correlate with the expression of specific sets of genes, including nuclear factors and classical mechanotransduction pathways. This versatile device thus enables the precise control of cell and nuclear deformation by confinement and the correlative study of the associated molecular events.
The first World Cell Race
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Maiuri P, Terriac E, Paul-Gilloteaux P, Vignaud T, McNally K, Onuffer J, Thorn K, Nguyen PA, Georgoulia N, Soong D, Jayo A, Beil N, Beneke J, Hong Lim JC, Pei-Ying Sim C, Chu YS; WCR participants, Jiménez-Dalmaroni A, Joanny JF, Thiery JP, Erfle H, Parson
Curr Biol. - 22(17) :R673-5 - DOI:10.1016/j.cub.2012.07.052 - 2012
Motility is a common property of animal cells. Cell motility is required for embryogenesis [1], tissue morphogenesis [2] and the immune response [3] but is also involved in disease processes, such as metastasis of cancer cells [4]. Analysis of cell migration in native tissue in vivo has yet to be fully explored, but motility can be relatively easily studied in vitro in isolated cells. Recent evidence suggests that cells plated in vitro on thin lines of adhesive proteins printed onto culture dishes can recapitulate many features of in vivo migration on collagen fibers [5,6]. However, even with controlled in vitro measurements, the characteristics of motility are diverse and are dependent on the cell type, origin and external cues. One objective of the first World Cell Race was to perform a large-scale comparison of motility across many different adherent cell types under standardized conditions. To achieve a diverse selection, we enlisted the help of many international laboratories, who submitted cells for analysis. The large-scale analysis, made feasible by this competition-oriented collaboration, demonstrated that higher cell speed correlates with the persistence of movement in the same direction irrespective of cell origin.
Predicting division plane position and orientation
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Minc N, Piel M.
Trends Cell Biol. - 22(4) :193-200 - DOI:10.1016/j.tcb.2012.01.003 - 2012
Predicting cellular behavior is a major challenge in cell and developmental biology. Since the late nineteenth century, empirical rules have been formulated to predict the position and orientation of mitotic cleavage planes in plant and animal cells. Here, we review the history of division plane orientation rules and discuss recent experimental and theoretical studies that refine these rules and provide mechanistic insights into how division can be predicted. We describe why some of these rules may better apply to certain cell types and developmental contexts and discuss how they could be integrated in the future to allow the prediction of division positioning in tissues.
Anthrax receptors position the spindle
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Minc N, Piel M
Nat. Cell Biol. - 15(1) :11-3 - DOI:10.1038/ncb2664 - 2012
Oriented mitosis is essential during tissue morphogenesis. The Wnt/planar cell polarity (Wnt/PCP) pathway orients mitosis in a number of developmental systems, including dorsal epiblast cell divisions along the animal-vegetal (A-V) axis during zebrafish gastrulation. How Wnt signalling orients the mitotic plane is, however, unknown. Here we show that, in dorsal epiblast cells, anthrax toxin receptor 2a (Antxr2a) accumulates in a polarized cortical cap, which is aligned with the embryonic A-V axis and forecasts the division plane. Filamentous actin (F-actin) also forms an A-V polarized cap, which depends on Wnt/PCP and its effectors RhoA and Rock2. Antxr2a is recruited to the cap by interacting with actin. Antxr2a also interacts with RhoA and together they activate the diaphanous-related formin zDia2. Mechanistically, Antxr2a functions as a Wnt-dependent polarized determinant, which, through the action of RhoA and zDia2, exerts torque on the spindle to align it with the A-V axis.
Microfabricated devices for cell biology: all for one and one for all
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Lautenschläger F, Piel M
Curr Opin Cell Biol - 25(1) :116-24 - DOI:10.1016/j.ceb.2012.10.017 - 2012
Individual cells in their native physiological states face a dynamic multi-factorial environment. This is true of both single-celled and multi-cellular organisms. A key challenge in cell biology is the design of experimental methods and specific assays to disentangle the contribution of each of the parameters governing cell behavior. After decades of studying cells cultured in Petri dishes or on glass coverslips, researchers can now benefit from a range of recent technological developments that allow them to study cells in a variety of contexts, with different levels of complexity and control over a range of environmental parameters. These technologies include new types of microscopy for detailed imaging of large cell aggregates or even whole tissues, and the development of cell culture substrates, such as 3D matrices. Here we will review the contribution of a third type of tool, collectively known as microfabricated tools. Derived from techniques originally developed for microelectronics, these tools range in size from hundreds of microns to hundreds of nanometers.
Monitoring Single Cell Bioenergetics via the Coarsening of Emulsion Droplets
Laboratoire Colloïdes et Matériaux Divisés - L. Boitard, D. Cottinet, C. Kleinschmitt, N. Bremond, J. Baudry, G. Yvert, J. Bibette
Proc. Nat. Acad. Sci. USA - 109(19) :7181-6 - DOI:10.1073/pnas.1200894109 - 2012
Microorganisms are widely used to generate valuable products, and their efficiency is a major industrial focus. Bioreactors are typically composed of billions of cells, and available measurements only reflect the overall performance of the population. However, cells do not equally contribute, and process optimization would therefore benefit from monitoring this intrapopulation diversity. Such monitoring has so far remained difficult because of the inability to probe concentration changes at the single-cell level. Here, we unlock this limitation by taking advantage of the osmotically driven water flux between a droplet containing a living cell toward surrounding empty droplets, within a concentrated inverse emulsion. With proper formulation, excreted products are far more soluble within the continuous hydrophobic phase compared to initial nutrients (carbohydrates and salts). Fast diffusion of products induces an osmotic mismatch, which further relaxes due to slower diffusion of water through hydrophobic interfaces. By measuring droplet volume variations, we can deduce the metabolic activity down to isolated single cells. As a proof of concept, we present the first direct measurement of the maintenance energy of individual yeast cells. This method does not require any added probes and can in principle apply to any osmotically sensitive bioactivity, opening new routes for screening, and sorting large libraries of microorganisms and biomolecules.

635 publications.