ABSTRACT
Double-walled carbon nanotubes (DWNTs) prepared by catalytic chemical vapour deposition were functionalized in such a way that they were optimally designed as a nano-vector for the delivery of small interfering RNA (siRNA), which is of great interest for biomedical research and drug development. DWNTs were initially oxidized and coated with a polypeptide (Poly(Lys:Phe)), which was then conjugated to thiol-modified siRNA using a heterobifunctional cross-linker. The obtained oxDWNT-siRNA was characterized by Raman spectroscopy inside and outside a biological environment (mammalian cells). Uptake of the custom-designed nanotubes was not associated with detectable biochemical perturbations in cultured cells, but transfection of cells with DWNTs loaded with siRNA targeting the green fluorescent protein (GFP) gene, serving as a model system, as well as with therapeutic siRNA targeting the survivin gene, led to a significant gene silencing effect, and in the latter case a resulting apoptotic effect in cancer cells.
Subject(s)
Biomedical Research/methods , Nanotubes, Carbon/chemistry , Apoptosis , Cell Line, Tumor , Flow Cytometry , Gene Silencing , Green Fluorescent Proteins/metabolism , Humans , RNA, Small Interfering/metabolism , Spectrum Analysis, Raman , Time FactorsABSTRACT
Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot.
ABSTRACT
We present a comparative study of several non-covalent approaches to disperse, debundle and non-covalently functionalize double-walled carbon nanotubes (DWNTs). We investigated the ability of bovine serum albumin (BSA), phospholipids grafted onto amine-terminated polyethylene glycol (PL-PEG(2000)-NH(2)), as well as a combination thereof, to coat purified DWNTs. Topographical imaging with the atomic force microscope (AFM) was used to assess the coating of individual DWNTs and the degree of debundling and dispersion. Topographical images showed that functionalized DWNTs are better separated and less aggregated than pristine DWNTs and that the different coating methods differ in their abilities to successfully debundle and disperse DWNTs. Height profiles indicated an increase in the diameter of DWNTs depending on the functionalization method and revealed adsorption of single molecules onto the nanotubes. Biofunctionalization of the DWNT surface was achieved by coating DWNTs with biotinylated BSA, providing for biospecific binding of streptavidin in a simple incubation step. Finally, biotin-BSA-functionalized DWNTs were immobilized on an avidin layer via the specific avidin-biotin interaction.
