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Individual SnO(2) nanowires were integrated in suspended micromembrane-based bottom-up devices. Electrical contacts between the nanowires and the electrodes were achieved with the help of electron- and ion-beam-assisted direct-write nanolithography processes. The stability of these nanomaterials was evaluated as function of time and applied current, showing that stable and reliable devices were obtained. Furthermore, the possibility of modulating their temperature using the integrated microheater placed in the membrane was also demonstrated, enabling these devices to be used in gas sensing procedures. We present a methodology and general strategy for the fabrication and characterization of portable and reliable nanowire-based devices.

The conformational analysis of the ionophore metal complex salinomycin-Na by N M R spectroscopy and molecular dynamics (MD) calculation was carried out in solution to study a model for ion transport across biological membranes. The first N M R solution structure of an ionophore metal complex using NOE-derived distances is reported. The 51 distance constaints derived from a 600-MHz NOESY spectrum of this molecule in the extreme narrowing limit were in agreement with an overall macrocyclic solution structure. The back-calculation of the NOESY spectrum confirmed the reliability of the NOE data. The structure was first refined by MD simulation in vacuo without a sodium ion present and subsequently in solution in the presence of a sodium ion. The complex shows a hydrophobic surface and a hydrophilic core, with the ion coordinated by a distorted pentagonal pyramid of oxygen atoms. Additional free MD simulations with and without the ion provide further information about the exact hinge regions and a possible mechanism of ionophoric action.

Gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. These devices were found to work at much lower temperatures (T≈280 °C) and bias voltages (V≈2 V) than their micro-counterparts, thereby demonstrating the inherent potential of individual nanostructures in building functional nanodevices. High selectivity of our miniaturized sensors emerges from the dissimilar sensing mechanisms of those typical of standard resistive-type sensors (RES). Therefore, by employing this detection principle (SI) together with RES measurements, better selectivity than that observed in standard metal oxide sensors could be demonstrated. Simplicity and specificity of the gas detection as well as low-power consumption make these single nanowire devices promising technological alternatives to overcome the major drawbacks of solid-state sensor technologies.

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