Synthesis of water-soluble phosphonate functionalized single-walled carbon nanotubes and their applications in biosensing

Abstract

A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of single-walled carbon nanotubes (SWNTs) by π–π stacking interactions between naphthalen-1-ylmethylphosphonic acid (NYPA) and SWNTs. Ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR) spectroscopy and zeta potential analysis confirm the phosphonate groups noncovalently attach on the SWNTs surface, in accordance with the prediction of molecular dynamics (MD) simulations. The phosphonate functionalized SWNTs have good solubility in polar solvent due to the big electrostatic repulsion between phosphonate groups, the strong hydration force of phosphonate groups and the partial debundling of SWNTs. X-ray diffraction (XRD) and Raman spectroscopy measurements demonstrate the water-soluble phosphonate functionalized SWNTs almost completely preserve the electronic and structural integrity of the pristine SWNTs. Meanwhile, the as-prepared phosphonate functionalized SWNTs show good biocompatibility for protein immobilization. Consequently, myoglobin (Mb) proteins immobilized on the phosphonate functionalized SWNTs show excellent bioelectrocatalytic activity towards the reduction of hydrogen peroxide due to the exciting electronic properties of the phosphonate functionalized SWNTs and the fast electron transfer rate of Mb.