Trace identification of cysteine enantiomers based on an electrochemical sensor assembled from Cu_xS@SOD zeolite

The nonchiral sensor concept based on a sodalite (SOD) zeolite loaded Cu_xS (Cu_xS@SOD) catalyst is proposed as a sensing platform for chiral cysteine (Cys) determination. Chiral Cys is analyzed by the difference of binding capacity between Cu_xS catalysts. The observed current in amperometric i-t curve (A i-t C) is always positive for the L-cysteine (L-Cys), while it is negative for the D-cysteine (D-Cys). Under differential pulse voltammetry (DPV) method, the characteristic current peak for the Cu_xS@SOD moves to right (positive potential position) with the addition of L-Cys while it moves to left (negative potential direction) with the addition of D-Cys, respectively. Cyclic voltammetry (CV) is consistent with DPV and discusses the diffusion control mechanism. In this work, the ultra-trace determination of cysteine enantiomers reaches the limit of detection (LOD) of 0.70 fM and 0.60 fM by the highly efficient Cu_xS catalyst restrained in the nanosized SOD zeolite cages of the opening window pores, respectively. The sensor opens up a novel potential prospect for achiral composite in the field of chiral recognition through electrochemical methods with extra-low concentration.