Lipid-Modulated Assembly of Magnetized Iron-Filled Carbon Nanotubes in Millimeter-Scale Structures

Abstract

Biomolecule-functionalized carbon nanotubes (CNTs) combine the molecular recognition properties of biomaterials with the electrical properties of nanoscale solid state transducers. Application of this hybrid material in bioelectronic devices requires the development of methods for the reproducible self-assembly of CNTs into higher-order structures in an aqueous environment. To this end, we have studied pattern formation of lipid-coated Fe-filled CNTs, with lengths in the 1-5 mm range, by controlled evaporation of aqueous CNT-lipid suspensions. Novel diffusion limited aggregation structures composed of endto-end oriented nanotubes were observed by optical and atomic force microscopy. Significantly, the lateral dimension of assemblies of magnetized Fe-filled CNTs was in the millimeter range. Control experiments in the absence of lipids and without magnetization indicated that the formation of these long linear nanotube patterns is driven by a subtle interplay between radial flow forces in the evaporating droplet, lipid-modulated van der Waals forces, and magnetic dipole-dipole interactions.

Carbon nanotube self-assembly with lipids and detergent: a molecular dynamics study

“…The observation of a cylindrical micelle of lipids surrounding a CNT is of interest, suggesting that lipids may be used to solubilize CNTs. This is supported by recent experiments on (derivatized) CNTs which suggest solubilization by lipids may indeed be possible [33].…”

A review of the microstructure and rheology of carbon nanotube suspensions

“…To enhance the magnetic susceptibility of CNTs, some researchers strategically incorporated paramagnetic or ferromagnetic materials using various chemical and physical methods as reviewed by Samouhos and McKinley [78]. Toledo and co-workers [24], for example, studied pattern formation during the drying of an aqueous CNT/lipid suspension and showed that aggregate structures were altered in the presence of a magnetic field.…”

“…Other characterization techniques reported in the literature include polarized Raman microscopy [81][82][83], X-ray diffraction [84,85], near-infrared fluorescence microscopy [86], and tagging CNTs with fluorescent markers [87][88][89][90]. Besides in situ characterization, the orientation distribution of CNTs can also be characterized indirectly by performing electron microscopy on extruded or cured samples (see, for example, references [24], [47], [91], and [92]).…”