We present a thermodynamic evaluation of the self-assembly of charged nanometer-sized particles at the water/oil interface. The chemical potentials of the nanoparticles in the bulk (aqueous) phase and at the water/oil interface are calculated taking into account interfacial energies, van der Waals interactions, and electrostatic repulsions. An isotherm of the interfacial particle density as a function of the surface charge density on the particles is obtained and compared with experimental results on gold and CdTe nanoparticles self-assembled at the water/heptane interface. Our model provides a semi-quantitative explanation for the spontaneous self-assembly of several types of metallic and semiconducting charged nanoparticles upon reduction of their surface charge.
We have studied electrostatic layer-by-layer spraying assembly of inorganic/organic nanocomposite multilayered films consisting of Au nanoparticle (Au NP) and photosensitive polycation nitrodiazoresin (NDR). A uniform growth of the Au NP-based assembly film is revealed by UV−vis spectroscopy and AFM-film thickness measurements. We demonstrate that cross-linked films can be produced by UV irradiation which induces the conversion of originally ionic bonds into covalent ones. The nanostructure of the film such as the thickness and the fraction of Au NP can be tailored by the adsorption conditions. Thus, we find that the mechanical properties, which were measured using a buckling test method, can be tailored to a certain degree.
The immobilization of cells in defined arrays (cell patterning) is a key step towards cell-based biosensors or other cell-based devices. While cell patterning is usually achieved by modifying the surface on which only the cells should adhere and leaving the cells unmodified, we present here a different approach in which cells are first coated with polyelectrolytes and subsequently immobilized on patterned surfaces. By coating, the cells are protected and their interactions with the substrate are modified such that patterning is simplified. We used microcontact printing of polyelectrolytes to structure surfaces such that regions of opposite charges and the same charge as the cell coating were present and found that we can thus achieve patterning of the coated yeast cells. In accordance with prior work, we find that coating does not kill the cells and coated GFP-expressing cells still function after immobilization, which we checked by fluorescence microscopy.
In this paper, we show that it is possible to direct the adhesion of polyelectrolyte microcapsules to patterned substrates. The patterned substrate contains regions of like and oppositely charged polyelectrolyte coatings: Adhesion of microcapsules is blocked by regions of the substrate containing like charges, while we find strong adhesion on oppositely charged regions. The approach is completely based on self-assembly and can be performed under ambient laboratory conditions. We demonstrate that it is thus possible to isolate individual microcapsules, with enclosed volumes on the order of femtoliters, and create arrays. This strategy could find applications in the field of combinatorial chemistry or sensing techniques where the capsules can serve as reaction volumes or containers for sensing agents, respectively.
rate was kept at 100 sccm. After the furnace had cooled to room temperature, a white wool-like product was deposited on the silicon substrate and the temperature of the cold zone was about 1050 C. The collected products were characterized by SEM (FESEM; JEOL JSM 6700F), HRTEM (JEOL 2010, at 200 kV), and EDX attached to the HRTEM. The dielectric properties of the products were measured by a dielectric relaxation spectrometer (Hioki 3531Z HiTESTER) The development of lab-on-a-chip technologies has attracted considerable attention in the past decade because miniaturized devices offer exciting opportunities for analytical, bio-, and synthetic chemistry, as well as for materials science. Downscaling allows the design of portable devices that are capable of performing complete analysis of samples, so-called total analysis systems (see a review by Jakeway et al.[1] ), reduces the amounts of reagents and speeds up processing and reaction times owing to reduced lengths in the device and the correspondingly shorter diffusion times. Finally, lowcost, mass-produced microfluidic chips can be readily adapted for massive parallel analysis or syntheses that work with ultrasmall quantities. A central challenge for downscaling remains the improvement of existing and the development of new device architectures that allow transport, separation, and analysis of reagents. In this communication, we present a novel and versatile approach to integrating semipermeable membranes with thicknesses down to 50 nm in soft lithographic structures.[2] We show that these membranes act as diffusion barriers for macromolecules, while they are permeable for lowmolecular-weight species, which makes them interesting for separation purposes. In addition, such a membrane can be used as an osmotic pressure sensor if its deflection resulting from a pressure difference is monitored. Here, we focus on the first aspect, investigating arrays of micrometer-sized cavities filled with entrapped macromolecules and covered with membranes that are permeable for low-molecular-weight spe-COMMUNICATIONS
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