Publications
172 results found
Miller RM, Poulos AS, Robles ESJ, et al., 2016, Isothermal Crystallization Kinetics of Sodium Dodecyl Sulfate–Water Micellar Solutions, Crystal Growth & Design, Vol: 16, Pages: 3379-3388, ISSN: 1528-7505
The crystallization mechanisms and kinetics of micellar sodium dodecyl sulfate (SDS) solutions in water, under isothermal conditions, were investigated experimentally by a combination of reflection optical microscopy (OM), differential scanning calorimetry (DSC), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The rates of nucleation and growth were estimated from OM and DSC across temperatures ranging from 20 to −6 °C for 20% SDS-H2O, as well as for 10 and 30% SDS-H2O at representative temperatures of 6, 2, and −2 °C. A decrease in temperature increased both nucleation and growth rates, and the combined effect of the two processes on the morphology was quantified via both OM and ATR-FTIR. Needles, corresponding to the hemihydrate polymorph, become the dominant crystal form at ≤ −2 °C, while platelets, the monohydrate, predominate at higher temperatures. Above 8 °C, crystallization was only observed if seeded from crystals generated at lower temperatures. Our results provide quantitative and morphological insight into the crystallization of ubiquitous micellar SDS solutions and its phase stability below room temperature.
Bolognesi G, Saito Y, Tyler AI, et al., 2016, Mechanical characterization of ultralow interfacial tension oil-in-water droplets by thermal capillary wave analysis in a microfluidic device., Langmuir, Vol: 32, Pages: 3580-3586, ISSN: 1520-5827
Measurements of the ultralow interfacial tension and surfactant film bending rigidity for micron-sized heptane droplets in AOT-NaCl aqueous solutions were performed in a microfluidic device through the analysis of thermally-driven droplet interface fluctuations. The Fourier spectrum of the stochastic droplet interface displacement was measured through bright-field video microscopy and contour analysis technique. The droplet interfacial tension together with the surfactant film bending rigidity were obtained by fitting the experimental results to the prediction of a capillary wave model. Compared to existing methods for ultralow interfacial tension measurements, this contactless non-destructive all-optical approach has several advantages, such as fast measuring, easy implementation, cost-effectiveness, reduced amount of liquids and integration into lab-on-a-chip devices.
Carreras P, Elani Y, Law RV, et al., 2015, A microfluidic platform for size-dependent generation of droplet interface bilayer networks on rails, Biomicrofluidics, Vol: 9, ISSN: 1932-1058
Dropletinterface bilayer (DIB) networks are emerging as a cornerstone technology for the bottom up construction of cell-like and tissue-like structures and bio-devices. They are an exciting and versatile model-membrane platform, seeing increasing use in the disciplines of synthetic biology, chemical biology, and membrane biophysics. DIBs are formed when lipid-coated water-in-oil droplets are brought together—oil is excluded from the interface, resulting in a bilayer. Perhaps the greatest feature of the DIB platform is the ability to generate bilayer networks by connecting multiple droplets together, which can in turn be used in applications ranging from tissue mimics, multicellular models, and bio-devices. For such applications, the construction and release of DIB networks of defined size and composition on-demand is crucial. We have developed a droplet-based microfluidic method for the generation of different sized DIB networks (300–1500 pl droplets) on-chip. We do this by employing a droplet-on-rails strategy where droplets are guided down designated paths of a chip with the aid of microfabricated grooves or “rails,” and droplets of set sizes are selectively directed to specific rails using auxiliary flows. In this way we can uniquely produce parallel bilayer networks of defined sizes. By trapping several droplets in a rail, extended DIB networks containing up to 20 sequential bilayers could be constructed. The trapped DIB arrays can be composed of different lipid types and can be released on-demand and regenerated within seconds. We show that chemical signals can be propagated across the bio-network by transplanting enzymatic reaction cascades for inter-droplet communication.
Barriga HMG, Law RV, Seddon JM, et al., 2015, The effect of hydrostatic pressure on model membrane domain composition and lateral compressibility, Physical Chemistry Chemical Physics, ISSN: 1463-9084
Phase separation in ternary model membranes is known to occur over a range of temperatures and compositions and can be induced by increasing hydrostatic pressure. We have used small angle X-ray scattering (SAXS) to study phase separation along pre-determined tie lines in dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC) and cholesterol (CHOL) mixtures. We can unequivocally distinguish the liquid ordered (Lo) and liquid disordered (Ld) phases in diffraction patterns from biphasic mixtures and compare their lateral compressibility. The variation of tie line endpoints with increasing hydrostatic pressure was determined, at atmospheric pressure and up to 100 MPa. We find an extension and shift of the tie lines towards the DOPC rich region of the phase diagram at increased pressure, this behaviour differs slightly from that reported for decreasing temperature.
Findlay H, Purushothaman S, Ces O, et al., 2015, Secondary transporter structure and function in synthetic lipid bilayer systems, 29th Annual Symposium of the Protein-Society, Publisher: WILEY-BLACKWELL, Pages: 50-51, ISSN: 0961-8368
McDonald C, Jovanovic G, Ces O, et al., 2015, Membrane Stored Curvature Elastic Stress Modulates Recruitment of Maintenance Proteins PspA and Vipp1, mBio, Vol: 6, Pages: e01188-15-e01188-15, ISSN: 2161-2129
Phage shock protein A (PspA), which is responsible for maintaining inner membrane integrity under stress in enterobacteria, and vesicle-inducting protein in plastids 1 (Vipp1), which functions for membrane maintenance and thylakoid biogenesis in cyanobacteria and plants, are similar peripheral membrane-binding proteins. Their homologous N-terminal amphipathic helices are required for membrane binding; however, the membrane features recognized and required for expressing their functionalities have remained largely uncharacterized. Rigorously controlled, in vitro methodologies with lipid vesicles and purified proteins were used in this study and provided the first biochemical and biophysical characterizations of membrane binding by PspA and Vipp1. Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane. PspA has an enhanced sensitivity for SCE stress and a higher affinity for the membrane than Vipp1. These variations in binding may be crucial for some of the proteins’ differing roles in vivo. Assays probing the transcriptional regulatory function of PspA in the presence of vesicles showed that a relief of transcription inhibition occurs in an SCE stress-specific manner. This in vitro recapitulation of membrane stress-dependent transcription control suggests that the Psp response may be mounted in vivo when a cell’s inner membrane experiences increased SCE stress.
Gaffney PRJ, ces O, arduin A, 2015, Regulation of PLCβ2 by the electrostatic and mechanical properties of lipid bilayers, Scientific Reports, Vol: 5, ISSN: 2045-2322
Phosphoinositide-specific phospholipase C (PLC) is an important family of enzymes constituting a junction between phosphoinositide lipid signaling and the trans-membrane signal transduction processes that are crucial to many living cells. However, the regulatory mechanism of PLC is not yet understood in detail. To address this issue, activity studies were carried out using lipid vesicles in a model system that was specifically designed to study protein-protein and lipid-protein interactions in concert. Evidence was found for a direct interaction between PLC and the GTPases that mediate phospholipase activation. Furthermore, for the first time, the relationships between PLC activity and substrate presentation in lipid vesicles of various sizes, as well as lipid composition and membrane mechanical properties, were analyzed. PLC activity was found to depend upon the electrostatic potential and the stored curvature elastic stress of the lipid membranes.
Purushothaman S, Cicuta P, Ces O, et al., 2015, The Influence of high pressure on the bending rigidity of model membranes, Journal of Physical Chemistry B, Vol: 119, Pages: 9805-9810, ISSN: 1520-6106
Curvature is a fundamental lipid membrane property that influences many membrane-mediated biological processes and dynamic soft materials. One of the key parameters that determines the energetics of curvature change is the membrane bending rigidity. Understanding the intrinsic effect of pressure on membrane bending is critical to understanding the adaptation and structural behavior of bio-membranes in deep-sea organisms, as well as soft material processing. However, it has not previously been possible to measure the influence of high hydrostatic pressure on membrane bending energetics and this bottleneck has primarily been due to a lack of technology platforms for performing such measurements. We have developed a new high pressure microscopy cell which, combined with vesicle fluctuation analysis, has allowed us to make the first measurements of membrane bending rigidity as a function of pressure. Our results show a significant increase in bending rigidity at pressures up to 40 MPa. Above 40 MPa, the membrane mechanics become more complex. Corresponding small and wide angle X-ray diffraction shows an increase in density and thickness of the bilayer with increasing pressure which correlates with the micro-mechanical measurements and these results are consistent with recent theoretical predictions of the bending rigidity as a function of hydrocarbon chain density. This technology has the potential to transform our quantitative understanding of the role of pressure in soft material processing, the structural behavior of bio-membranes and the adaptation mechanisms employed by deep-sea organisms.
Willison KR, Salehi-Reyhani A, Burgin E, et al., 2015, Absolute quantification of protein copy number in single cells using single molecule microarrays, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, Vol: 44, Pages: S179-S179, ISSN: 0175-7571
Seddon JM, Brooks NJ, Ces O, et al., 2015, Lipid bicontinuous cubic phases: effects of chain-branching and hydrostatic pressure, 10th European-Biophysical-Societies-Association (EBSA) European Biophysics Congress, Publisher: SPRINGER, Pages: S187-S187, ISSN: 0175-7571
McCarthy NL, Ces O, Law RV, et al., 2015, Separation of liquid domains in model membranes induced with high hydrostatic pressure, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, Vol: 44, Pages: S115-S115, ISSN: 0175-7571
Barriga H, Tyler A, McCarthy NL, et al., 2015, Engineering swollen bicontinuous cubic phases and cubosomes; a new generation of artificial cells, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, Vol: 44, Pages: S109-S109, ISSN: 0175-7571
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Elani Y, Law RV, Ces O, 2015, Vesicle-based artificial cells: recent developments and prospects for drug delivery, THERAPEUTIC DELIVERY, Vol: 6, Pages: 541-543, ISSN: 2041-5990
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- Citations: 13
McCarthy NLC, Ces O, Law RV, et al., 2015, Separation of liquid domains in model membranes induced with high hydrostatic pressure, Chemical Communications, Vol: 51, Pages: 8675-8678, ISSN: 1364-548X
We have imaged the formation of membrane microdomains immediately after their induction using a novel technology platform coupling high hydrostatic pressure to fluorescence microscopy. After formation, the ordered domains are small and highly dynamic. This will enhance links between model lipid assemblies and dynamic processes in cellular membranes.
Barriga HMG, Bazin R, Templer RH, et al., 2015, Buffer-Induced Swelling and Vesicle Budding in Binary Lipid Mixtures of Dioleoylphosphatidylcholine:Dioleoylphosphatidylethanolamine and Dioleoylphosphatidylcholine:Lysophosphatidylcholine Using Small-Angle X-ray Scattering and <SUP>31</SUP>P Static NMR, LANGMUIR, Vol: 31, Pages: 2979-2987, ISSN: 0743-7463
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- Citations: 1
Tang T-YD, Brooks NJ, Ces O, et al., 2015, Structural studies of the lamellar to bicontinuous gyroid cubic (Q<sub>II</sub><SUP>G</SUP>) phase transitions under limited hydration conditions, SOFT MATTER, Vol: 11, Pages: 1991-1997, ISSN: 1744-683X
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- Citations: 9
Tyler AII, Barriga HMG, Parsons ES, et al., 2015, Electrostatic swelling of bicontinuous cubic lipid phases, Soft Matter, Vol: 11, Pages: 3279-3286, ISSN: 1744-6848
Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in-vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by a) increasing the bilayer stiffness by adding cholesterol and b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å.
Barriga HMG, Parsons ES, McCarthy NLC, et al., 2015, Pressure-Temperature Phase Behavior of Mixtures of Natural Sphingomyelin and Ceramide Extracts, Langmuir, Vol: 31, Pages: 3678-3686, ISSN: 1520-5827
Elani Y, Law R, Ces O, 2015, Vesicle-based artificial cells: recent developments and prospects for drug delivery, Therapeutic delivery, ISSN: 2041-6008
Salehi-Reyhani A, Gesellchen F, Mampallil D, et al., 2015, Chemical-Free Lysis and Fractionation of Cells by Use of Surface Acoustic Waves for Sensitive Protein Assays, ANALYTICAL CHEMISTRY, Vol: 87, Pages: 2161-2169, ISSN: 0003-2700
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- Citations: 27
Barriga HMG, Tyler AII, McCarthy NLC, et al., 2015, Temperature and pressure tuneable swollen bicontinuous cubic phases approaching nature's length scales, Soft Matter, Vol: 11, Pages: 600-607, ISSN: 1744-683X
Bicontinuous cubic structures offer enormous potential in applications ranging from protein crystallisation to drug delivery systems and have been observed in cellular membrane structures. One of the current bottlenecks in understanding and exploiting these structures is that cubic scaffolds produced in vitro are considerably smaller in size than those observed in biological systems, differing by almost an order of magnitude in some cases. We have addressed this technological bottleneck and developed a methodology capable of manufacturing highly swollen bicontinuous cubic membranes with length scales approaching those seen in vivo. Crucially, these cubic systems do not require the presence of proteins. We have generated highly swollen Im3m symmetry bicontinuous cubic phases with lattice parameters of up to 480 Å, composed of ternary mixtures of monoolein, cholesterol and negatively charged lipid (DOPS or DOPG) and we have been able to tune their lattice parameters. The swollen cubic phases are highly sensitive to both temperature and pressure; these structural changes are likely to be controlled by a fine balance between lipid headgroup repulsions and lateral pressure in the hydrocarbon chain region.
Elani Y, Law RV, Ces O, 2015, Protein synthesis in artificial cells: using compartmentalisation for spatial organisation in vesicle bioreactors, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 15534-15537, ISSN: 1463-9076
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- Citations: 86
Furse S, Mak L, Tate EW, et al., 2015, Synthesis of unsaturated phosphatidylinositol 4-phosphates and the effects of substrate unsaturation on <i>Sop</i>B phosphatase activity, ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 13, Pages: 2001-2011, ISSN: 1477-0520
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- Citations: 7
Elani Y, Purushothaman S, Booth PJ, et al., 2015, Measurements of the effect of membrane asymmetry on the mechanical properties of lipid bilayers, CHEMICAL COMMUNICATIONS, Vol: 51, Pages: 6976-6979, ISSN: 1359-7345
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- Citations: 76
Bolognesi G, Hargreaves A, Ward AD, et al., 2015, Microfluidic generation and optical manipulation of ultra-low interfacial tension droplets, Conference on Integrated Photonics - Materials, Devices, and Applications III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
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- Citations: 1
Casey D, Wylie D, Gallo J, et al., 2015, A novel, all-optical tool for controllable and non-destructive poration of cells with single-micron resolution, Bio-Optics: Design and Application 2015, Publisher: Optical Society of America
We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near-IR laser interacting with thin-layer amorphous silicon substrates. This technique will allow new experiments in single-cell biology, particularly in neuroscience.
Bolognesi G, Hargreaves A, Ward AD, et al., 2014, Microfluidic generation of monodisperse ultra-low interfacial tension oil droplets in water, RSC Advances, Vol: 5, Pages: 8114-8121, ISSN: 2046-2069
We present a novel microfluidic approach for the generation of monodisperse oil droplets in water with interfacial tensions of the order of 1 μN m−1. Using an oil-in-water emulsion containing the surfactant aerosol OT, heptane, water and sodium chloride under conditions close to the microemulsion phase transition, we actively controlled the surface tension at the liquid–liquid interface within the microfluidic device in order to produce monodisperse droplets. These droplets exhibited high levels of stability with respect to rupture and coalescence rates. Confirmation that the resultant emulsions were in the ultra-low tension regime was determined using real space detection of thermally-induced capillary waves at the droplet interface.
Karamdad K, Law RV, Seddon JM, et al., 2014, Preparation and mechanical characterisation of giant unilamellar vesicles by a microfluidic method, Lab on a Chip, Vol: 15, Pages: 557-562, ISSN: 1473-0197
Giant unilamellar vesicles (GUVs) have a wide range of applications in biology and synthetic biology. As a result, new approaches for constructing GUVs using microfluidic techniques are emerging but there are still significant shortcomings in the control of fundamental vesicle structural parameters such as size, lamellarity, membrane composition and internal contents. We have developed a novel microfluidic platform to generate compositionally-controlled GUVs. Water-in-oil (W/O) droplets formed in a lipid-containing oil flow are transferred across an oil- water interface, facilitating the self-assembly of a phospholipid bilayer. In addition, for the first time we have studied the mechanical properties of the resultant lipid bilayers of the microfluidic GUVs. Using fluctuation analysis we were able to calculate the values for bending rigidity of giant vesicles assembled on chip and demonstrate that these correlate strongly with those of traditional low throughput strategies such as electroformation.
Salehi-Reyhani A, Burgin E, Ces O, et al., 2014, Addressable droplet microarrays for single cell protein analysis, ANALYST, Vol: 139, Pages: 5367-5374, ISSN: 0003-2654
Ces O, Elani Y, Law R, 2014, Vesicle-based artificial cells as chemical microreactors with spatially segregated reaction pathways, Nature Communications, Vol: 5, Pages: 1-5, ISSN: 2041-1723
In the discipline of bottom-up synthetic biology, vesicles define the boundaries of artificial cells and are increasingly being used as biochemical microreactors operating in physiological environments. As the field matures, there is a need to compartmentalize processes in different spatial localities within vesicles, and for these processes to interact with one another. Here we address this by designing and constructing multi-compartment vesicles within which an engineered multi-step enzymatic pathway is carried out. The individual steps are isolated in distinct compartments, and their products traverse into adjacent compartments with the aid of transmembrane protein pores, initiating subsequent steps. Thus, an engineered signalling cascade is recreated in an artificial cellular system. Importantly, by allowing different steps of a chemical pathway to be separated in space, this platform bridges the gap between table-top chemistry and chemistry that is performed within vesicles.
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