Highly selective determination of cysteine using a composite prepared from multiwalled carbon nanotubes and gold nanoparticles stabilized with calcium crosslinked pectin

We describe a glassy carbon electrode (GCE) modified with gold nanoparticles that were stabilized with calcium-crosslinked pectin (CCLP) and electrodeposited on multiwalled carbon nanotubes (MWCNTs) by cyclic voltammetry. The resulting electrode was used for the selective determination of L-cysteine (L-Cys). Its characterization showed that the CCLP acts as a scaffold to form highly stable, uniform and electrochemically active AuNPs. Electrochemical studies showed the MWCNT to significantly promote the electrodeposition of the CCLP-AuNPs. The new GCE exhibited excellent electrocatalytic ability towards oxidation of L-Cys in showing a lower overpotential and giving a higher oxidation peak current. The diffusion coefficient for the oxidation of L-Cys was calculated to be 3.0 × 10−6 cm2 s−1. This amperometric sensor displays a wide linear range (from 0.1 to 1,000 μM), high sensitivity (0.46 μA μM−1 cm−2) and a detection limit as low as 19 nM (at a signal-to-noise ratio of 3). The sensor was applied to specifically detect L-Cys even in the presence of 500-fold excess of interferents. It also is stable and possesses good repeatability and reproducibity, and was successfully applied to the determination of L-Cys in spiked samples of human serum.