The electrophoretic transport of ions through single wall carbon nanotubes (SWCNTs) of diameters between 1.2 and 1.8 nm was studied for different monovalent chloride salts using microfluidic devices incorporating either a single or a few CNTs in parallel. The ionic conductance was found to be about one order of magnitude higher than expected from a simple electro-migration behavior without any surface effect. Importantly, the ionic conductance measured for different cations did not scale with their bulk electrophoretic mobility thus indicating a probable selective cation transport through these sub-2 nm SWCNTs. The transport of Na+ was notably found to be favored in comparison to that of Li+ and Cs+ or K+ . These results highlight the influence of steric and surface effects induced by the nano-confinement on the transport of ions through sub-2 nm SWCNTs.

Monitoring individual single-walled carbon nanotubes (SWCNTs) during their growth is a highly sought-after goal in view of understanding the processes involved in the nucleation, elongation and termination which ultimately control the diameter and chiral selectivity. Here, we report on the first truly in situ observations of SWCNT growth in an environmental scanning electron microscope (ESEM). The CNT growth from lithographically patterned catalysts was investigated as a function of the catalyst type (Fe, Co or Ni), temperature, type of precursor (ethanol or acetylene), gas phase composition and pressure, and pretreatment conditions, and we report on the most appropriate conditions for SWCNT growth in ESEM conditions. We show that this approach allows the observation at the submicron scale of the different steps of the nanotube synthesis including the catalyst reduction, the growth and percolation of the nanotube network, and the deposition of individual nanotubes grown in the gas phase on the substrate. Despite these obvious advantages, we identified a few limitations which will need to be tackled for fully taking advantage of the approach, for instance for monitoring the growth of individual SWCNTs by ESEM, including the short lifetime of the catalyst nanoparticles, the preference for kite growth (by opposition to surface growth) and the influence of the electron beam on the nanotube growth.

Liquid phase encapsulation of α-sexithiophene (6T) molecules inside individualized single-walled carbon nanotubes (SWCNTs) is investigated using Ramanimaging and spectroscopy. By taking advantage of the strong Raman response of this system, we probe the encapsulation isotherms at 30°C and 115°C using a statistical ensemble of SWCNT deposited on a Si/SiO2 substrate. Two distinct and sequential stages ofencapsulation are observed: Stage 1 is a one-dimensional (1D) aggregation of 6T alignedhead-to-tail inside the nanotube and stage 2 proceeds with the assembly of a second row, giving pairs of aligned 6Ts stacked together side-by-side. The experimental data are fitted using both Langmuir (type VI) and Ising models, in which the single-aggregate (stage 1) forms spontaneously whereas the pair-aggregate (stage 2) is endothermic in toluene with formation enthalpy of 8Hpair = 260±20 meV. Tunable Raman spectroscopy for each stage reveals a bathochromic shift of the molecular resonance of the pair-aggregate, which is consistent with strong inter-molecular coupling and suggestive of J-type aggregation. This quantitative Raman approach is sensitive to roughly 10 molecules per nanotube andprovides direct evidence of molecular entry from the nanotube ends. These insights into the encapsulation process guide the preparation of well-defined 1D molecular crystals having tailored optical properties.

Biological nano-channels expressed in living cells, where they ensure keyphysiological functions, feature outstanding efficiency in terms of both ionselectivity and conductivity. The latter generally exceeds, by 3 to 4 orderof magnitude, the values expected from classical hydrodynamics. This propertyof biological nano-channels may result from their pore width in the rangeof the Debye length (0.3-30 nm) and this currently grounds many researchworks aimed at developing the use of solid-state porous nano-materials for‘‘high-throughput’’ molecular and ion sensing or sorting, with applicationssuch as drug delivery, energy conversion, water desalination and others. Singlewalled carbon nanotubes (SWNTs), which make nano-pores with welldefinedstructural and physical properties, may allow us to overcomingmany limitations of other nano-materials. The possibility of transportingions and molecules through these SWNTs has already been reported by othergroups (Lee et al., 2010, Science 329:1320; Liu et al., 2010, Science 327:64).In this context, we aim at studying the usableness of SWNT-incorporating devicesfor discriminating ions and single small biomolecules, using nucleotidesand amino acids as model compounds. Here, we will present the first part ofthis work, which consists in the fabrication of microfluidic devices incorporatingindividual SWNTs and the study of ion transport inside these devicesusing ionic current measurements, i.e. patch-clamp type. A study of the selectivityof these SWNTs will be also shown using different cations-basedelectrolytes.