A sensitive signal-on electrochemiluminescence sensor based on a nanocomposite of polypyrrole-Gd2O3 for the determination of L-cysteine in biological fluids.

A sensitive solid-state electrochemiluminescence (ECL) electrode for L-cysteine was developed based on depositing layers of a hybrid nanocomposite of polypyrrole-dodecyl benzene sulfate-sodium perchlorate-sodium carbonate-gadolinium (PPy-Gd2O3) on a platinum substrate. The presence of the Gd2O3 nanoparticle layer improved the ECL signal, and under optimum conditions, a linear relationship was observed between the signal and the logarithm of L-cysteine concentration from 1.0 × 10-13 to 1.0 × 10-6 M (R2 = 0.9937). At the emission wavelength around 425 nm , at which the analytical signal was measured, the electrode showed an RSD of less than 4% and a low detection limit of 4.2 × 10-14 M. The results proved to be reproducible and stable, and the electrode was applicable in the determination of L-cysteine in biological fluids with recoveries from 94.0-107%. Graphical abstract The results of this research indicated that the weak ECL of luminol is greatly improved by traces of L-cysteine on a solid-state platinum electrode coated with polypyrrole and gadolinium oxide nanoparticles (NPs) and have hence been effectively used in the analysis of L-cysteine in plasma and saliva.