The selection and assembly of materials are central issues in the development of smaller, more flexible batteries. Cobalt oxide has shown excellent electrochemical cycling properties and is thus under consideration as an electrode for advanced lithium batteries. We used viruses to synthesize and assemble nanowires of cobalt oxide at room temperature. By incorporating gold-binding peptides into the filament coat, we formed hybrid gold-cobalt oxide wires that improved battery capacity. Combining virus-templated synthesis at the peptide level and methods for controlling two-dimensional assembly of viruses on polyelectrolyte multilayers provides a systematic platform for integrating these nanomaterials to form thin, flexible lithium ion batteries.

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Virus-Enabled Synthesis and Assembly of Nanowires for Lithium Ion Battery Electrodes

The corrosion of metals is one of the main destructive processes that leads to huge economic losses. Polymer coating systems are normally applied on a metal surface to provide a dense barrier against the corrosive species in order to protect metal structures from corrosive attack. When the barrier is damaged and the corrosive agents penetrate to the metal surface the coating system can not stop the corrosion process. The most effective solution so far for designing anticorrosion coatings for active protection of metals is to employ chromate-containing conversion coatings. However, hexavalent chromium species are responsible for several diseases, including DNA damage and cancer, which is the main reason for banning Cr-containing anticorrosion coatings in Europe from 2007. The deposition of thin inorganic or hybrid films on metallic surfaces has been suggested as a pretreatment to provide an additional barrier against the corrosion species and mainly to improve adhesion between the metal and polymer coating system. The films are usually deposited by the plasma polymerization technique or the sol–gel route. Sol–gel-derived thin films that contain either inorganic (phosphates, vanadates, borates, and cerium and molybdenum compounds) or organic (phenylphosphonic acid, mercaptobenzothiazole, mercaptobenzoimidazole, triazole) inhibitors are investigated as substitutes for chromates. Among them, the highest activity is shown for sol–gel coatings with a cerium dopant of a critical concentration in the 0.2–0.6 wt % range. However, the negative effect of the free inhibitor occluded in the sol–gel matrix on the stability of the protective film is observed for all types of inhibitors (for instance, a higher concentration of Ce leads to the formation of microholes in the sol–gel film). This shortcoming calls for the development of nanometer-scale reservoirs to isolate an inhibitor inside and prevent its direct interaction with the sol–gel matrix. Nanoreservoirs should be homogeneously distributed in the film matrix and should possess controlled and corrosion-stimulated inhibitor release to cure corrosion defects. Mixed-oxide nanoparticles (e.g. ZrO2/CeO2), [4] b-cyclodextrin-inhibitor complexes, hollow polypropylene fibers, and conducting polyaniline have been explored as prospective reservoirs for corrosion inhibitors to be incorporated in the protective film. The common mechanism of the nanoreservoir activity is based on the slow release of inhibitor triggered by corrosion processes. Ion exchangers have also been investigated as ‘smart’ reservoirs for corrosion inhibitors. Chemically synthesized hydrocalmite behaves as an anion exchanger: adsorbing corrosive chloride ions and releasing corrosion-inhibiting nitrite anions. Despite considerable efforts devoted to the development of new, complex anticorrosion systems, practically no single solution is able to fulfill the requirements of sufficient corrosion protection while avoiding chromates in the coating, especially in the case of aluminum alloys used for aerospace applications. The recently developed technology of layer-by-layer (LbL) deposition of oppositely charged species (polyelectrolytes, nanoparticles, enzymes, dendrimers) from their solutions on the substrate surface represents an interesting approach to prepare reservoirs with regulated storage/release properties assembled with nanometer-thickness precision. LbL coatings are of practical interest in photonics (optical filters, luminescent coatings), electrocatalysis (electrodes for DNA transfer, enzyme-catalyzed oxidation), as membranes, and chemical reactors. LbL-assembled polyelectrolyte multilayers reveal controlled permeability properties. Depending on the nature of the assembled monolayers, the permeability of multilayer films can be controlled by changing pH, ionic strength, and temperature, or by applying magnetic or electromagnetic fields. Polyelectrolyte assemblies have never been used in corrosion-protection coatings, although storage of corrosion inhibitors in polyelectrolyte multilayers can confer several advantages: they can prevent a negative effect of the corrosion inhibitor on the stability of the coating, decrease the influence of the coating polymerization on the inhibitor, and provide intelligent release of the corrosion inhibitor, as the permeability C O M M U N IC A TI O N S

Layer‐by‐Layer Assembled Nanocontainers for Self‐Healing Corrosion Protection

Stimuli-responsive LbL capsules and nanoshells for drug delivery.

Drug delivery into biological cells is an important and growing area of application. Among other systems, such as gels, polymeric micelles, liposomes, and colloids, nanoengineered polyelectrolyte multilayer microcapsules offer a unique opportunity to combine surface multifunctionality with design flexibility for the delivery of encapsulated materials into designated compartments and cells. Furthermore, microcapsules can be arranged in arrays for imaging, could be appropriate candidates for a cell-sorting system, and serve as fluorescence markers for the characterization of cells by fluorescence-activated cell sorting (FACS). The capsules are fabricated using the layer-bylayer (LbL) method by alternately adsorbing oppositely charged polymers on colloidal templates followed by core dissolution. In this regard, proteins and biocompatible polymers have also received increased interest. The main advantage of such a method is the precise control over the chemical composition of the surfaces. In the area of biomedical applications, polyelectrolytemultilayer capsules are envisioned for the delivery of encapsulated materials into biological cells. Recently, we have presented the real-time monitoring and remote release of encapsulated materials from polyelectrolyte-multilayer capsules on the single-capsule level. Such an approach is different from the studies reported by other research groups in that it is performed on a single-capsule level, which is the method ideally suited to applications where precise control is necessary. In addition, the distinctive feature reported in reference [10b] is the measurement of the temperature rise induced locally by absorption of laser light by nanoparticles. In general, nanoparticles are becoming ubiquitous components that link chemistry and physics with biology and biochemistry. They can be embedded in the walls of capsules to provide functionality, and they are also finding increasing interest for biological imaging. Herein, we show that polyelectrolyte-multilayer capsules containing metallic nanoparticles in their walls can be remotely activated to release encapsulatedmaterial inside living cells. Fluorescently labeled polymers were chosen as a model system for encapsulated materials. The remote-release experiments were conducted according to the following scheme. The polyelectrolyte-multilayer shells were doped with metal nanoparticles, which served as absorption centers for energy supplied by a laser beam. These absorption centers cause local heating that disrupts the local polymer matrix and allows the encapsulated material to leave the interior of the capsule. When using lasers with biological objects, it is important to minimize the absorption of laser light by cells and tissue. This can be accomplished by choosing the laser wavelength in the biologically “friendly” window—the near-infrared (NIR) part of the spectrum. Usually the spectral properties of water serve as a good criterion, as it constitutes 80–85% of eukaryotic cells. Indeed, in water the temperature rise in the focus of a laser diode with wavelength 850 nm and operating at optical powers up to 100 mW during less than 1 s exposure time was reported to be under 1 K. Other important parameters that control the interaction of laser light with the absorption centers are the size of the nanoparticles and their concentration on the microcapsules. The concentration of metal nanoparticles plays an important role for two reasons: 1) when the distance between the two adjacent nanoparticles is of the order of their size, the thermal effects produced by [*] Dr. A. G. Skirtach, Dr. O. Kreft, K. K hler, Prof. Dr. H. M hwald, Prof. Dr. G. B. Sukhorukov Institut f+r Grenzfl-chen Max-Planck-Institut f+r Kolloidund Grenzfl-chenforschung Am M+hlenberg 1, 14424 Golm/Potsdam (Germany) Fax: (+49)331-567-9202 E-mail: andre.skirtach@mpikg-golm.mpg.de

Laser-induced release of encapsulated materials inside living cells

In this review, the recent achievements in the synthesis of inorganic nanomaterials inside the spatially confined volume of individual micro- and submicroreactors (emulsions, micelles, organized thin films, polyelectrolyte capsules, etc.) are presented. The advantages and shortcomings of each type of microreactor are discussed. Particular attention is paid to polyelectrolyte capsules as confined microreactors with controlled shell permeability and the possibility of shell engineering on the nanolevel, thus tailoring different functionalities. Nanomaterials synthesized inside a confined multifunctional microreactor have several advantages: i) absence of particle aggregates, ii) amorphous or metastable crystal phases, and iii) unique composite inorganic/inorganic and inorganic/organic structures.

Nanoparticle synthesis in engineered organic nanoscale reactors

The layer-by-layer (LBL) deposition technique has been applied to the design of polymer electrolyte films appropriate for electrochemical applications such as sensors and electrochromic cells. In this work, we describe the properties of three LBL polymer electrolyte systems assembled from cationic layers of linear poly(ethylene imine) (LPEI), with anionic layers of Nafion, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), and poly(acrylic acid) (PAA). The assembly behavior of these systems was carefully examined, and ionic conductivity was determined using impedance spectroscopy. The influences of assembly conditions and water plasticization on ion conduction were elaborated. Room-temperature ionic conductivity greater than 10-5 S/cm can be achieved within LPEI/PAMPS and LPEI/PAA films, which is 2 orders of magnitude greater than the highest values previously described in LBL films. By manipulating a unique assembly mechanism, high ionic conductivity can be achieved in LPEI/PAMPS films at low pl...

Dean M. DeLongchamp and

Papers

Fast Ion Conduction in Layer-By-Layer Polymer Films