Stable non-covalent functionalisation of multi-walled carbon nanotubes by pyrene–polyethylene glycol through π–π stacking

Abstract

Carbon nanotubes (CNTs) are good candidates to construct nanostructured, implantable micro-electrodes since they are conductive materials and may increase the overall electrode surface area, and thus the signal/noise ratio. However, the adsorption of biomolecules on CNTs is well-known to lead to a surface passivation. In this context, a surface modification appears essential to overcome these limitations. In this paper, the non-covalent functionalisation of multi-walled carbon nanotubes (MWNTs) by pyrene–PEG molecules through π–π stacking is presented. We describe in the first part the functionalisation of MWNT powders in aqueous solution for which we obtained a stable dispersion of functionalised MWNTs. The stability of the non-covalently functionalised MWNT dispersion during 7 cycles of dialysis in H₂O was studied by UV spectroscopy. The density of pyrene–PEG on the MWNT surface stabilised at about 4 × 10¹¹ molecules mm⁻² after 4 cycles of dialysis (all the free pyrene–PEG molecules were removed by dialysis). Next, this non-covalent functionalisation of MWNT arrays on a substrate was examined. After the functionalisation, the increase of the MWNT wettability led to a 50-fold increase of the capacitance of the MWNT nanostructured electrode. Finally, we chose streptavidin, a well-known adhesive protein, as an example to test the efficiency of functionalised MWNTs towards preventing non-specific adsorption. The result shows that the presence of pyrene–PEG on the MWNT surface is indeed efficient.