Figure 11 Sensing responses of CNT and Au-CNT samples towards the detection of hydrogen (H 2 ). Behaviour of pure CNTs (a) and find more hybrid Au-CNT samples prepared by dip-coating (b) and drop-casting (c). Maximum sensitivity value for each peak as a function of H2 concentration (d). Solid line in d graph represents the linear fit to these

CFTR inhibitor data points. In both cases, CNT and Au-CNT hybrids, increased resistance under acetylene or hydrogen exposure has been detected. This behavior is typical of p-type semiconductors exposed to electron donor gases, since these species induce a reduction of the density of holes [59]. Particularly for Au-CNT hybrid nanostructures, the sensing mechanism could be explained by two process: (1) the adsorption of gases in the side walls of CNTs, with the simultaneous charge transfer between

the target molecule and the CNT network; and (2) the gold nanoclusters could be producing a catalytic spillover effect, in which the electron donor gases are chemisorbed and their electrons transferred from the gold particles to the CNT, decreasing the conductivity of the p-type material. It is worth mentioning at this point that the presence of the AuNPs can modify the catalytic activity of the hybrids not only due to the presence of the particles themselves but also because of the structural changes they induce in the walls of the CNTs, thus modifying the intrinsic chemical affinity of the tubes. The difference in sensitivity of the gold-modified CNTs in this report, BEZ235 chemical structure Molecular motor compared to previous reports [59, 60], could be due to the lower density of NPs used in the

course of this study. This report indicates that hybrid materials formed by AuNPs, encapsulated by the CNTs, are useful as sensing elements; nevertheless, further characterizations are indeed required in order to incorporate them in practical devices. Conclusions Through the procedures described in this report, we have indeed formed a nanoscale reactor with physical dimensions that can be designed by adjusting the synthesis procedure. These reactors are fairly uniform in diameter and while protected by AAOs, added particles, precursors, or molecules only can access the inside of the tubes. As a way to prove the effectiveness of this strategy, we have selectively located Au ions inside the tubes’ cavities. Depending on the preparation conditions, the AuNPs can be made to evolve from small NPs, with diameter only dependent on the precursor concentration, to larger conglomerates with sizes that are fixed by the CNT’s confinement. The alumina can be easily dissolved releasing the new CNT-particle hybrids. From the study of the conductance as a function of temperature, we found that the dominant transport mechanism in the CNTs_(AAO/650°C) and the Au-CNTs samples is the intra-tube 1D hopping. This is consistent with the fact the CNTs’ walls contain a considerable fraction of amorphous carbon.