A high-performance electrochemical sensor for biologically meaningful L-cysteine based on a new nanostructured L-cysteine electrocatalyst

As a new class of L-cysteine electrocatalyst explored in this study, Au/CeO₂ composite nanofibers (CNFs) were employed to modify the screen printed carbon electrode (SPCE) to fabricate a novel L-cysteine (CySH) electrochemical sensor with high performance. Its electrochemical behavior and the roles of Au and CeO₂ in the composite toward electro-oxidation of CySH were elucidated and demonstrated using cyclic voltammetry and amperometry techniques for the first time through the comparison with pure CeO₂ NFs. More specifically, the Au/CeO₂ CNFs modified SPCE possessed greatly enhanced electrocatalytic activity toward CySH oxidation. An ultra high sensitivity of 321 μA mM⁻¹cm⁻² was obtained, which is almost 2.7 times higher than that of pure CeO₂ NFs, revealing that the presence of Au imposed an important influence on the electrocatalytic activity toward CySH. The detailed reasons on such high performance were also discussed. In addition, the as-prepared sensor showed a low detection limit of 10 nM (signal to noise ratio of 3), a wide linear range up to 200 μM for the determination of CySH, an outstanding reproducibility and good long-term stability, as well as an excellent selectivity against common interferents such as tryptophan, tyrosine, methionine, ascorbic acid and uric acid. All these features indicate that the Au/CeO₂ composite nanofiber is a promising candidate as a new class of L-cysteine electrocatalyst in the development of highly sensitive and selective CySH electrochemical sensor.