Sensitive and selective electrochemical sensing of l-cysteine based on a caterpillar-like manganese dioxide–carbon nanocomposite

A novel one-dimensional (1-D) caterpillar-like manganese dioxide–carbon (MnO2–C) nanocomposite has been synthesized by a direct redox reaction between carbon nanotubes (CNTs) and permanganate ions for the first time. The as-prepared nanostructured MnO2–C composite mainly consisting of ε-MnO2 nanoflakes had a unique microstructure, high specific surface area (200 m2 g−1) and favourable conductivity. The nanostructured MnO2–C composite, added as a modification to the glassy carbon (GC) electrode via a direct electrochemical co-deposition process with a chitosan hydrogel, was found to exhibit excellent catalytic activity toward L-cysteine electro-oxidation because the specific interaction between the –SH group of L-cysteine and solid MnO2 occurred to form surface complexes. A determination of L-cysteine at the MnO2–C/chitosan/GC (MnO2–C/chit/GC) electrode was carried out by amperometric measurement. Under the optimum experimental conditions, the detection response for L-cysteine was fast (within 7 s). The logarithm of catalytic currents shows a good linear relationship with that of the L-cysteine concentration in the range of 0.5–680 μM (R = 0.9986), with a low detection limit of 22 nM. The MnO2–C/Chit/GC electrode exhibited excellent stability (without any decrease of the response signal after 1 month) and admirable resistance against interference like glutathione and other oxidizable amino acids (tryptophan, tyrosine, L-lysine and methionine).