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)]

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)]

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)]

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)]

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)]