Publications by Type: Journal Articles

Miller OJ, Bernath K, Agresti JJ, Amitai G, Kelly BT, Mastrobattista E, Taly V, Magdassi S, Tawfik DS, Griffiths AD. Directed evolution by in vitro compartmentalization. Nat. MethodsNature Methods. 2006;3 (7) :561 - 570.Abstract
The goal of in vitro compartmentalization (IVC) is to divide a large reaction between many microscopic compartments. This technique was first developed to generate "artificial cells" for the directed evolution of proteins. Typically, an aq. soln. of genes and an in vitro transcription-translation system is stirred (or homogenized) into an oil-surfactant mixt. to create a water-in-oil (w/o) emulsion with -1010 aq. droplets per mol of emulsion. The majority of droplets contain no more that a single gene along with all of the mol. machinery needed to express that gene. The expressed proteins and the products of their catalytic activities cannot leave the droplets, and so genotype is coupled to phenotype in vitro, making it possible to select very large libraries of genes (108-1011 genes). We describe the advantages and applications of IVC. A protocol for performing a directed evolution expt. by IVC makes use of one or more w/o emulsions. This procedure involves the generation of a gene library, the performance of a selection, and the subsequent recovery of the selected genes by PCR. We also describe two procedures for converting w/o emulsions to water-in-oil-in-water (w/o/w) emulsions for high-throughput screening using a fluorescence-activated cell sorter (FACS). Finally, we describe two methods for delivering substrates, regulators and other compds. to the preformed aq. droplets of w/o emulsion. [on SciFinder(R)]
Sen T, Magdassi S, Nizri G, Bruce IJ. Dispersion of magnetic nanoparticles in suspension. Micro Nano Lett.Micro & Nano Letters [Internet]. 2006;1 (1) :39 - 42. Publisher's VersionAbstract
Pure magnetite nanoparticles (Fe3O4) have been synthesized in water by copptn. using two different approaches (from ferrous sulfate and a mixt. of ferrous and ferric chlorides). All materials aggregated in aq. suspension, but their subsequent dispersion on treatment with a variety of agents was obsd. to be different. Magnetite produced using ferrous sulfate could not be disaggregated, whereas magnetite produced from a mixt. of ferrous and ferric chlorides could be disaggregated to a quasi-monodispersed form. The dispersing agents were tetra-Me ammonium hydroxide, Disperbyk 190 and polyacrylic acid. The finding has potentially important implications for the surface activation of superparamagnetic magnetite nanoparticles and their ability to be used in bio/life science applications. [on SciFinder(R)]
Magdassi S, Kamyshny A, Grouchko M. Making connections. Aqueous dispersions of silver nanoparticles form conductive inkjet inks. Eur. Coat. J.European Coatings Journal. 2006;(11) :54, 56, 58-59.Abstract
Nanoparticles of metals having high elec. cond. offer new scope for direct digital printing of conductive patterns. Stable aq. silver nanoparticle dispersions were synthesized by chem. redn. These were suitable for inkjet printing, with the dried inks sintering at temps. as low as 160°. However, the resistance remained much higher than that of metallic silver. [on SciFinder(R)]
Nizri G, Magdassi S. Solubilization of hydrophobic molecules in nanoparticles formed by polymer-surfactant interactions. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 2005;291 (1) :169 - 174.Abstract
The interaction between the anionic surfactant, Na dodecyl sulfate, and the polyelectrolyte, poly(diallyldimethylammonium chloride), may give nanoparticles dispersed in H2O. The morphol. of the resulting nanoparticles and their ability to solubilize hydrophobic mols. were evaluated. As shown by SEM and AFM imaging, the particles are spherical, having a diam. of ∼20 nm. The solubilization within the nanoparticles was tested with pyrene, a fluorescence probe, and Nile Red, a solvatochromic probe. For Nile Red the solubilization within the nanoparticles is at lower polarity than for SDS micelles, and from pyrene solubilization apparently the hydrophobicity of the nanoparticles depends on the ratio between the SDS mols. and the charge unit of the polymer. [on SciFinder(R)]
Bernath K, Magdassi S, Tawfik DS. Directed Evolution of Protein Inhibitors of DNA-nucleases by in Vitro Compartmentalization (IVC) and Nano-droplet Delivery. J. Mol. Biol.Journal of Molecular Biology. 2005;345 (5) :1015 - 1026.Abstract
In vitro compartmentalization (IVC) uses water-in-oil emulsions to create artificial cell-like compartments in which genes can be individually transcribed and translated. Here, we present a new application of IVC for the selection of DNA-nuclease inhibitors. We developed a nano-droplets delivery system that allows the transport of various solutes, including metal ions, into the emulsion droplets. This transport mechanism was used to regulate the activity of colicin nucleases that were co-compartmentalized with the genes, so that the nucleases were activated by nickel or cobalt ions only after the potential inhibitor genes have been translated. Thus, genes encoding nuclease inhibitors survived the digestion and were subsequently amplified and isolated. Selection is therefore directly for inhibition, and not for binding of the nuclease. The stringency of selection can be easily modulated to give high enrichments (100-500-fold) and recoveries. We demonstrated its utility by selecting libraries of the gene encoding the cognate inhibitor of colicin E9 (immunity protein 9, or Im9) for inhibition of another colicin (ColE7). The in vitro evolved inhibitors show significant inhibition of ColE7 both in vitro and in vivo. These Im9 variants carry mutations into residues that det. the selectivity of the natural counterpart (Im7) while completely retaining the residues that are conserved throughout the family of immunity protein inhibitors. The in vitro evolution process confirms earlier hypotheses regarding the "dual recognition" binding mechanism and the way in which new colicin-immunity pairs diverged from existing ones. [on SciFinder(R)]
Aharoni A, Amitai G, Bernath K, Magdassi S, Tawfik DS. High-Throughput Screening of Enzyme Libraries: Thiolactonases Evolved by Fluorescence-Activated Sorting of Single Cells in Emulsion Compartments. Chem. Biol. (Cambridge, MA, U. S.)Chemistry & Biology (Cambridge, MA, United States). 2005;12 (12) :1281 - 1289.Abstract
Single bacterial cells, each expressing a different library variant, were compartmentalized in aq. droplets of water-in-oil (w/o) emulsions, thus maintaining a linkage between a plasmid-borne gene, the encoded enzyme variant, and the fluorescent product this enzyme may generate. Conversion into a double, water-in-oil-in-water (w/o/w) emulsion enabled the sorting of these compartments by FACS, as well as the isolation of living bacteria cells and their enzyme-coding genes. We demonstrate the directed evolution of new enzyme variants by screening >107 serum paraoxonase (PON1) mutants, to yield 100-fold improvements in thiolactonase activity. In vitro compartmentalization (IVC) of single cells, each carrying >104 enzyme mols., in a vol. of <10 fL (fl), enabled detection and selection despite the fast, spontaneous hydrolysis of the substrate, the very low initial thiolactonase activity of PON1, and the use of difusable fluorescent products. [on SciFinder(R)]
Kamyshny A, Ben-Moshe M, Aviezer S, Magdassi S. Ink-jet printing of metallic nanoparticles and microemulsions. Macromol. Rapid Commun.Macromolecular Rapid Communications. 2005;26 (4) :281 - 288.Abstract
Two types of ink-jet inks are presented: ink contg. an aq. dispersion of silver nanoparticles and an oil-in-water microemulsion-based ink. The metallic ink contains nanoparticles of silver, which are formed in the presence of an ionic polymeric stabilizer. Sintering of the printed image obtained with the use of such silver-based inks at temps. as low as 300° C results in formation of patterns possessing noticeable cond. The microemulsion inks are based on a thermodynamically stable microemulsion, in which the dispersed oil phase is a volatile solvent contg. a water-insol. colorant. After contact of the jetted ink droplets with a substrate, nanodroplets of the microemulsion are converted into nanoparticles of the solubilized colorant. In some cases, it was found that the evapn. of microemulsion ink droplets leads to formation of rings composed of ordered nanoparticles. [on SciFinder(R)]
Magdassi S, Grouchko M, Toker D, Kamyshny A, Balberg I, Millo O. Ring Stain Effect at Room Temperature in Silver Nanoparticles Yields High Electrical Conductivity. LangmuirLangmuir. 2005;21 (23) :10264 - 10267.Abstract
We demonstrate that metallic rings formed spontaneously at room temp. via evapn. of aq. drops contg. silver nanoparticles (20-30 nm in diam.) exhibit high elec. cond. (up to 15% of that for bulk silver). The mechanism underlying this self-assembly phenomena is the "ring stain effect", where self-pinning is combined with capillary flow to form a ring consisting of close-packed metallic nanoparticles along the perimeter of a drying droplet. Our macroscopic and microscopic (applying conductive at. force microscopy) transport measurements show that the cond. of the ring, which has a metallic brightness, is orders of magnitude larger than that of corresponding aggregates developed without the ring formation, where high cond. is known to appear only after annealing at high temp. [on SciFinder(R)]
Marx G, Ben-Moshe M, Magdassi S, Gorodetsky R. Fibrinogen C-terminal peptidic sequences (Haptides) modulate fibrin polymerization. Thromb. HaemostasisThrombosis and Haemostasis. 2004;91 (1) :43 - 51.Abstract
We previously described synthetic peptides of 19-21 amino acid residues, homologous to the C-termini of fibrinogen Fib340 and Fib420, from the β-chain (Cβ), the extended αE chain (CαE) and near the end of the γ-chain (preCγ) which elicited attachment (haptotactic) responses from mesenchymal cells. We named these haptotactic peptides -Haptides. The effects of Haptides on fibrin clot formation was evaluated and their possible effects on platelet aggregation was examd. The Haptides Cβ, CαE and preCγ, (2-10 μM) increased fibrin clot turbidity and also decreased thrombin-induced clotting time. Higher concns. (>120 μM of Cβ or preCγ) induced fibrinogen pptn. even without thrombin. These ppts. exhibited different ultrastructure from thrombin-induced fibrin by scanning and transmission microscopy. C-terminal peptides of the other fibrinogen chains exerted no such effects. Sepharose beads covalently coated with either whole fibrinogen or Haptides (SB-Fib or SB-Haptide) highly adsorbed free FITCHaptides. In aq. soln., Haptides formed nano-particles with av. size of ∼150nm in diam. We suggest that such pos. charged aggregates could serve to nucleate and accelerate fibrin gel formation. These results also indicate that Cβ and preCγ sequences within fibrin(ogen) participate in the docking and condensation of fibrin(ogen) during its assembly into a fibrin clot. By contrast, Haptides up to 100μM did not bind to platelets, and had no effect on platelet aggregation. Our findings highlight the roles of the C-terminal sequences of the β and γ chains in fibrin(ogen) polymn. as well as in cell attachment. [on SciFinder(R)]
Nizri G, Magdassi S, Schmidt J, Cohen Y, Talmon Y. Microstructural Characterization of Micro- and Nanoparticles Formed by Polymer-Surfactant Interactions. LangmuirLangmuir. 2004;20 (11) :4380 - 4385.Abstract
We have studied the nano- and microparticles formed by complexation of poly(diallyldimethylammonium chloride) and SDS. The complexation phenomenon was characterized by light scattering and ζ-potential measurements. The nature of the complexes was revealed by direct-imaging cryogenic temp. transmission electron microscopy (cryo-TEM), showing nanometric details of the complexes formed around the point of neutralization. The images also reveal how those aggregates are solubilized by excess surfactant, first into faceted particles with threadlike micelles attached to their surfaces, prior to complete solubilization, then into lacelike aggregates, and finally into spheroidal micelles. The nanostructure of the complexes strongly suggests they are made of a hexagonal liq. cryst. phase. This was further supported by small-angle X-ray scattering (SAXS). [on SciFinder(R)]
Mumcuoglu KY, Magdassi S, Miller J, Ben-Ishai F, Zentner G, Helbin V, Friger M, Kahana F, Ingber A. Repellency of citronella for head lice: double-blind randomized trial of efficacy and safety. Isr Med Assoc JThe Israel Medical Association journal : IMAJ. 2004;6 (12) :756 - 9.Abstract
BACKGROUND: Head lice move easily from head to head. The lack of safe, effective repellents leads to reinfestation. OBJECTIVES: To test the efficacy of a slow-release citronella formulation as a repellent against the head louse. METHODS: During 4 months in 2003 a randomized, placebo-controlled double-blind clinical study was conducted in four elementary schools; 103 children were treated with the test formulation and 95 with a placebo. RESULTS: A significant difference was observed during the second examination 2 months later, when 12.0% of the children treated with the test repellent and 50.5% of those treated with placebo were infested with lice. A significant difference was also observed at the third examination 2 months later, when 12.4% of the children treated with the test repellent and 33.7% treated with placebo were infested. Overall, there were significant differences between those treated with the repellent and those treated with the placebo (15.4% and 55.1% respectively, P < 0.0001). Side effects were observed in 4.4% of children who disliked the odor of the formulation, and an additional 1.0% who complained of a slight itching and burning sensation. CONCLUSIONS: Use of an effective repellent could significantly lower the incidence of reinfestations, which would lower expenditure on lice control, including pediculicides, combs and products for nit removal, and the time spent on treatment and removal of the nits.[on SciFinder (R)]
Sommer AP, Ben-Moshe M, Magdassi S. Size-Discriminative Self-Assembly of Nanospheres in Evaporating Drops. J. Phys. Chem. BJournal of Physical Chemistry B. 2004;108 (1) :8 - 10.Abstract
Evapn. of liq. drops contg. nanospheres resulted in circular deposition patterns. The circularity of the patterns depended on the uniformity of the surface tension on the substrate. By employing binary suspensions, contg. two differently sized nanospheres, it was possible to modulate the fine structure of such rings. Slow evapn. on mirror-polished substrates resulted in well-ordered distributions, where larger particles self-assembled in dense hexagonal packages, forming apparently an external ring, deposited around the massive inner ring. Deposition started at the air/liq./solid-contact line. Results could inspire principles for the fabrication of optical devices and may be fruitfully used to design biomaterials with cell-selective properties. A simple model is employed to predict the radial arrangement of nanospheres in rings. Deviations from a std. order (predicted by the model) may be useful to detect biol. active nanoparticles. [on SciFinder(R)]
Ben Moshe M, Magdassi S, Cohen Y, Avram L. Structure of microemulsions with gemini surfactant studied by solvatochromic probe and diffusion NMR. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 2004;276 (1) :221 - 226.Abstract
The structure of microemulsions prepd. by the anionic gemini surfactant didodecyl di-Ph ether disulfonate (C12-DADS) was investigated by a solvatochromic probe and NMR diffusion measurements. The NMR measurements indicate the presence of bicontinuous and oil-in-water microemulsions depending on microemulsion compn. The absorbance spectra of the solvatochromic probe, Nile red, indicate the solubilization of the probe in different sites, in agreement with the NMR findings. It was also found that the microemulsions were capable of dissolving the hydrophobic probe, Nile red, up to four times better than expected if it were simply dissolved in the toluene phase. [on SciFinder(R)]
Ben-Moshe M, Magdassi S. Surface activity and micellar properties of anionic gemini surfactants and their analogues. Colloids Surf., AColloids and Surfaces, A: Physicochemical and Engineering Aspects. 2004;250 (1-3) :403 - 408.Abstract
The properties of didodecyldiphenylether disulfonate gemini-type surfactants were studied and compared to mono-alkylated and monosulfonated analogous surfactants. Dynamic and equil. surface tension measurements indicate that the gemini surfactants have a higher surface activity compared to that of the monoalkyl analogs. The gemini-type surfactants have much larger surface area per mol., opposite effect of C no. on CMC and considerable swelling of the micelles upon increasing surfactant concn. Detn. of aggregation nos. by fluorescence measurements reveals that the longer chain gemini surfactants form micelles having <10 mols. per micelle. [on SciFinder(R)]
Hai M, Bernath K, Tawfik D, Magdassi S. Flow Cytometry: A New Method To Investigate the Properties of Water-in-Oil-in-Water Emulsions. LangmuirLangmuir. 2004;20 (6) :2081 - 2085.Abstract
A new and facile method is presented to evaluate w/o/w emulsions contg. fluorescent markers by flow cytometry. Flow cytometry allows simultaneous measurement of w/o/w emulsion droplets "marked" with a fluorescent marker or "blank" without the need for complicated sample prepn. The yield of prepn. of the w/o/w emulsion and the release rate of the fluorescent marker FITC-BSA were investigated by this new method. The release fraction (after 24 h) of FITC-BSA from the w/o/w emulsion decreased with increasing concn. of FITC-BSA inside the internal phase, just like the release fraction of NaCl as marker from the w/o/w emulsion. Flow cytometry results show that the yield and release behavior in w/o/w emulsions are in agreement with results reported by more complicated methods. [on SciFinder(R)]
Magdassi S. Fundamentals of Interface and Colloid Science: Interface Tension by J. Lyklema. Colloids Surf., AColloids and Surfaces, A: Physicochemical and Engineering Aspects. 2004;238 (1-3) :159.
Bernath K, Hai M, Mastrobattista E, Griffiths AD, Magdassi S, Tawfik DS. In vitro compartmentalization by double emulsions: sorting and gene enrichment by fluorescence activated cell sorting. Anal. Biochem.Analytical Biochemistry. 2004;325 (1) :151 - 157.Abstract
Water-in-oil (w/o) emulsions can be used to compartmentalize and select large gene libraries for a predetd. function. The aq. droplets of the w/o emulsion function as cell-like compartments in each of which a single gene is transcribed and translated to give multiple copies of the protein (e.g., an enzyme) it encodes. While compartmentalization ensures that the gene, the protein it encodes, and the products of the activity of this protein remain linked, it does not directly afford a way of selecting for the desired activity. Here the authors show that re-emulsification of w/o emulsions gives water-in-oil-in-water (w/o/w) emulsions with an external (continuous) water phase through which droplets contg. fluorescent markers can be isolated by fluorescence-activated cell sorting (FACS). These w/o/w emulsions can be sorted by FACS, while the content of the aq. droplets of the primary w/o emulsion remains intact. Consequently, genes embedded in these water droplets together with a fluorescent marker can be isolated and enriched from an excess of genes embedded in water droplets without a fluorescent marker. The ability of FACS instruments to sort up to 40,000 events per s may endow this technol. a wide potential in the area of high-throughput screening and the directed evolution of enzymes. [on SciFinder(R)]
Bernath K, Magdassi S, Tawfik DS. In vitro compartmentalization (IVC): A high-throughput screening technology using emulsions and FACS. Discov MedDiscovery medicine. 2004;4 (20) :49 - 53.Abstract
Extract: All screening approaches rely on ways of compartmentalizing assay reactions, and means of rapidly screening various molecules imbedded in these compartments. Miniaturization, which has become the hallmark of modern science and technology, has also been applied to screening, thus leading to a variety of high-throughput screening (HTS) technologies that aim at the smallest possible reaction volumes and the most sensitive and rapid means of detection. These demands are general and do not depend on the type of molecules (genes, proteins, small molecules, etc.) or activity (enzymatic, binding, inhibitory, etc.) that are being screened for, nor on the target of screening (functional genomics, directed evolution, drug discovery, etc.). Conventional HTS approaches use either robotic 2D-arrays (e.g., microtitre plates), or living cells. In vitro compartmentalization (IVC) is a newly developed technology that uses the aqueous droplets of water-in-oil (w/o) emulsions as cell-like compartments.[on SciFinder (R)]
Vaknin D, Dahlke S, Travesset A, Nizri G, Magdassi S. Induced crystallization of polyelectrolyte-surfactant complexes at the gas-water interface. Los Alamos Natl. Lab., Prepr. Arch., Condens. MatterLos Alamos National Laboratory, Preprint Archive, Condensed Matter [Internet]. 2004 :1-4, arXiv:cond-mat/0401194. Publisher's VersionAbstract
Synchrotron-x-ray and surface tension studies of a strong polyelectrolyte (PE) in the semi-dil. regime (∼O.1M monomer-charges) with varying surfactant concns. show that minute surfactant concns. induce the formation of a PE-surfactant complex at the gas/soln. interface. X-ray reflectivity and grazing angle x-ray diffraction (GIXD) provide detailed information of the top most layer, where the surfactant forms a 2-dimensional liq.-like monolayer, with a noticeable disruption of the structure of H2O at the interface. With the addn. of salt (NaCl) columnar-crystals with distorted-hexagonal symmetry are formed. [on SciFinder(R)]
Vaknin D, Dahlke S, Travesset A, Nizri G, Magdassi S. Induced Crystallization of Polyelectrolyte-Surfactant Complexes at the Gas-Water Interface. Phys. Rev. Lett.Physical Review Letters. 2004;93 (21) :218302/1 - 218302/4.Abstract
Synchrotron x-ray and surface-tension studies of a strong polyelectrolyte (PE) in the semidilute regime (∼0.1M monomer charges) with varying surfactant concns. show that minute surfactant concns. induce the formation of a PE-surfactant complex at the gas-soln. interface. X-ray reflectivity and grazing angle x-ray diffraction show the complex PE-surfactant resides at the interface and the alkyl chains of the surfactant form a two-dimensional liquidlike monolayer. With the addn. of salt (NaCl), columnar crystals with distorted-hexagonal symmetry are formed. [on SciFinder(R)]