Design and fabrication of low potential NADH-sensor based on poly(caffeic acid)@multi-walled carbon nanotubes

Abstract

We report on the chemical polymerization of caffeic acid (CA) on a multi-walled carbon nanotube surface (MWCNT). As a result, PCA24h@MWCNT nanostructure was obtained, which was then employed as a modifier for the glassy carbon electrode (GC). The GC/PCA@MWCNT electrode shows surface-confined redox peaks that strongly depend on the solution pH, which is characteristic of quinone/hydroquinone functionalities. Interestingly, by varying the time of synthesis, the redox couple's formal potential can be shifted toward negative values (below 0 V vs. Ag/AgCl at pH 7.4), which can be attributed to electron-donating effects provided by crosslinked bulky PCA. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) show that the PCA is covered on the surface of MWCNT. Physicochemical characterization including Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy revealed that PCA@MWCNT was successfully prepared with superior electron transfer ability. The GC/PCA@MWCNT modified electrode exhibits the excellent electrocatalytic ability to oxidize NADH at low potential. An amperometric method was developed to determine NADH based on its electrocatalytic oxidation with a sensitivity of 85.7 µA mM cm−2 and a limit of detection (LOD = 0.12 μM). The sensor had the advantages of high electrocatalytic activity and sensitivity.