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Optical activity is a fundamental phenomenon originating from the chiral nature of crystals and molecules. While intrinsic chiroptical responses of ordinary chiral materials to circularly polarized light are relatively weak, they can be enhanced by specially tailored nanostructures. Here, nanorod metamaterials, comprising a dense array of vertically aligned gold nanorods, is shown to provide significant enhancement of the circular dichroism response of an embedded material. A nanorod composite, acting as an artificial uniaxial crystal, is filled with chiral mercury sulfide nanocrystals embedded in a transparent polymer. The nanorod based metamaterial, being inherently achiral, enables optical activity enhancement or suppression. Unique properties of inherently achiral structures to tailor optical activities pave a way for flexible characterization of optical activity of molecules and nanocrystal-based compounds.

Silver nanoparticles exhibit antibacterial properties via bacterial inactivation and growth inhibition. The mechanism is not yet completely understood. This work was aimed at elucidating the effect of silver nanoparticles on inactivation of Escherichia coli, by studying particle-particle interactions in aqueous suspensions. Stable, molecularly capped, positively or negatively charged silver nanoparticles were mixed at 1 to 60microgmL(-1) with suspended E. coli cells to examine their effect on inactivation of the bacteria. Gold nanoparticles with the same surfactant were used as a control, being of similar size but made up of a presumably inert metal. Log reduction of 5log(10) and complete inactivation were obtained with the silver nanoparticles while the gold nanoparticles did not show any inactivation ability. The effect of molecularly capped nanoparticles on E. coli survival was dependent on particle number. Log reduction of E. coli was associated with the ratio between the number of nanoparticles and the initial bacterial cell count. Electrostatic attraction or repulsion mechanisms in silver nanoparticle-E. coli cell interactions did not contribute to the inactivation process.

The preparation of conductive and transparent gold/silver nanowire mesh films is reported. The nanowires formed after the reduction of the metal ions was triggered and a thin growth solution film was spread on a substrate. Metal reduction progressed within a template of a highly concentrated surfactant liquid crystalline mesostructure formed on the substrate during film drying to form ordered bundles of ultrathin nanowires. The films exhibited metallic conductivity over large areas, high transparency, and flexibility.

A simple wet chemical approach was developed for a unique on-surface synthesis of transparent conductive films consisting of ultrathin gold/silver nanowires directly grown on top of CdSe nanowire array photoconductive devices enclosed in polycarbonate membranes. The metal nanowire film formed an ohmic contact to the semiconductor nanowires without additional treatment. The sheet resistance and transparency of the metal nanowire arrays could be controlled by the number of metal nanowire layers deposited, ranging from ∼98–99% transmission through the visible range and several kOhm/sq sheet resistance for a single layer, to 80–85% transmission and ∼100 Ohm/sq sheet resistance for 4 layers.

The next generation of optoelectronic devices requires transparent conductive electrodes to be flexible, cheap, and compatible with large scale manufacturing processes. Indium Tin Oxide (ITO) electrodes are often used due to their superior transparency and conductance, however they are brittle, expensive and their fabrication requires vacuum conditions which restrict scale-up. One possible alternative to the traditional ITO electrode is the metal nanowire mesh (MNWM) electrode, which is transparent, conductive, flexible and easy to produce. In this work we present the preparation and characterization of a simple organic light emitting diode (OLED) device based on a transparent electrode made of ultrathin MNWM and a comparison to an ITO based device. We have found that MNWM electrodes offer a suitable alternative to ITO electrodes in OLED devices. We have also found that the failure rate for devices due to short circuits between the top and bottom electrodes was smaller in MNWM based devices compared to ITO based devices since the MNWM devices could be repaired to present normal OLED behavior by selectively burning the nanowires forming the short. The ability to “heal” organic devices presents an important advantage and also allows for future uses in applications such as roll to roll printing.