Amphiphilic phospholipids were used to direct the formation of biocompatible, uniform silica nanostructures in the presence of Saccharomyces cerevisiae and bacterial cell lines. The cell surfaces organize multilayered phospholipid vesicles that interface coherently with the silica host and help relieve drying stresses that develop with conventional templates. These host structures maintain cell accessibility, addressability, and viability in the absence of buffer or an external fluidic architecture. The cell surfaces are accessible and can be used to localize added proteins, plasmids, and nanocrystals. Prolonged cell viability combined with reporter protein expression enabled stand-alone cell-based sensing.

Long-range hydrophobic interactions operating underwater are important in the mediation of many natural and synthetic phenomena, such as protein folding, adhesion and colloid stability. Here we show that rough hydrophobic surfaces can experience attractive forces over distances more than 30 times greater than any reported previously, owing to the spontaneous evaporation of the intervening, confined water. Our finding highlights the importance of surface roughness in the interaction of extended structures in water, which has so far been largely overlooked.

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We have investigated inorganic cluster-surfactant materials to better understand the structural evolution of these phases as the surfactant:cluster ratio increases above 4:1 and the cluster charge increases beyond -4. Our studies suggest that both ordering of the surfactant molecules into bilayers as well as the cluster charge are the primary influences on the hybrid cluster-surfactant phase structure. However, cluster geometry, inclusion of solvent molecules, surfactant tail length, cation head size, etc. also influence the self-assembly of these materials. We present the synthesis, characterization, and single-crystal X-ray structure of [SiMo 12 O 40 ][C 16 H 33 N(CH 3 ) 3 ] 4 (monoclinic P2 1 /c, a ) 13.136(1) Å, b ) 20.139(2) Å, c ) 41.030(3) Å, β ) 93.443(1)°, and V ) 10834.7(17) Å 3 ) and the synthesis and characterization of a related phase that forms upon chemical reduction of the silicomolybdate anion. Structural and chemical comparisons are made between these two compounds, as well as other phases formed from polyoxometalates (with charges ranging from -3 to -16) and surfactants. The structure of [SiMo 12 O 40 ][C 16 H 33 N-(CH 3 ) 3 ] 4 is compared to the structures of other reported cluster-surfactant phases that also have a 1:4 cluster:surfactant ratio. Analyses of these phases provide some insight as to why it is thus far only this 1:4 ratio that provides crystals suitable for single-crystal diffraction studies and how the structure of the cluster-surfactant phases evolves as the surfactant/cluster ratio is increased.

When lipid-directed assembly of silicic acid precursors is conducted in the presence of living cells, the cells intervene, surrounding themselves with a fluid, multilayered lipid vesicle that interfaces coherently with an ordered silica mesophase. This bio/nano interface is unique in that its uniform nanostructure prevents excessive drying of water, maintaining cell viability, yet provides accessibility of the cell surface to small molecules. In comparison to existing immobilization schemes, such as encapsulation within sol-gel matrices, we show this interface to form by an active interplay between the living cell and surrounding matrix, which we refer to as cell-directed assembly (CDA). Importantly and perhaps uniquely, CDA creates a localized nanostructured microenvironment within which three-dimensional chemical gradients are established and maintained.

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Using sum-frequency vibrational spectroscopy, we found that water structure at nanoporous silica/water interfaces depended on the nanoporous film structure. For a periodic, self-assembled nanoporous film with monosized 2 nm pores occupying 20% of the top surface area, the surface vibrational spectrum was dominated by water in contact with silica, bare or covered by silane, at the top surface. It resembled the spectral characteristic of the hydrophilic water/silica or the hydrophobic water/silane interface. For a fractal nanoporous film with pores ranging from 5 to 50 nm in size occupying 90% of the top surface, the spectrum for a trimethyl silane-coated superhydrophobic porous film resembled largely that of a water/air interface. Only when the silane was completely removed would the spectrum revert to that characteristic of a hydrophilic water/silica interface. The surface charging behaviors of the bare nanoporous films in water with different pH were monitored by spectroscopic measurements and atomic force microscopy force measurements. The point of zero charge for the periodic porous film is around pH 2, similar to that of the flat silica surface. The point of zero charge could only be determined to be pH<6 for the fractal porous film because the thin fractal solid network limited the amount of surface charge and therefore, the accuracy of the measurements.

Membrane bilayers of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylethanolamine (DPPE) adsorbed to a freshly cleaved mica substrate have been imaged by Atomic Force Microscopy (AFM). The membranes were mounted for imaging by two methods: (a) by dialysis of a detergent solution of the lipid in the presence of the substrate material, and (b) by adsorption of lipid vesicles onto the substrate surface from a vesicle suspension. The images were taken in air, and show lipid bilayers adhering to the surface either in isolated patches or in continuous sheets, depending on the deposition conditions. Epifluorescence light-microscopy shows that the lipid is distributed on the substrate surfaces as seen in the AFM images. In some instances, when DPPE was used, whole, unfused vesicles, which were bound to the substrate, could be imaged by the AFM. Such membranes should be capable of acting as natural anchors for imaging membrane proteins by AFM.