"Fingertip"-guided noncovalent functionalization of carbon nanotubes by dendrons

Noncovalent functionalization of carbon nanotubes (CNTs) by dendrons was demonstrated. Certain types of dendrons successfully functionalized CNT surfaces through the noncovalent interactions between the peripheries of the dendrons and the sidewalls of CNTs. Dendrons have a unique anisotropic shape and an orthogonal functional group at their apex, and thus can generate a certain spacing between the functional groups upon immobilization on surfaces. Atomic force microscope (AFM) imaging, dispersion experiments, and MicroRaman spectroscopy were employed for the characterization of the functionalization. The binding was found to be governed by the chemical nature of the terminal groups, namely, the "fingertips", through a comparison study on the adsorption efficiency of the dendron analogs. Functional groups such as the carboxylic acid group and the benzyl amide group were effective for the cooperative binding. AFM analysis showed that the average spacing generated by the dendrons was 14-15 nm at a particular adsorption condition. Assembling streptavidin on the tubes through the dendrons and biotin confirmed the realization of the regulated spacing as well as the elimination of unwanted aggregation. The noncovalent functionalization of CNTs by a dendron can be a new approach toward sensible nanobiodevices, not only by introducing biomolecular probes on CNTs without disruption of the electronic network of the tubes, but also by providing the immobilized probe molecules with a space ample enough to minimize steric hindrance for the unhindered interaction with their target species.