Electrochemical reduction boosted Luminol cathodic electrochemiluminescence for trace chiral recognition of alanine enantiomers

Abstract

Electrochemiluminescence (ECL) is highly recommended in chiral recognition. ECL-based chiral sensors highly desire a sensitive sensing interface for signal conversion and absolute chiral discrimination. The ECL emission based on a luminol-dissolved O₂ system received much attention due to its nontoxicity and stability. However, the drawback of weak ECL emission hinders the fast signal conversion from chiral discrimination to ECL response. Herein, the amplification strategy of ECL emission is proposed based on the electrochemical reduction enhanced O₂ reduction reaction (ORR). Cadmium sulfide decorated on carbon-nanotubes (CdS/CNTs) with easy synthesis, wide-pH operation, and suitable valence-conduction band position is employed. Upon cathodic scan, the electrons transfer from electrochemically reduced-CdS/CNTs to O₂ and H₂O₂, thus accelerating the generation of reactive oxide species (ROS) and furthering ECL emission. Furthermore, the chiral ECL sensing interface is well-designed by combining the chiral recognition of D-amino acid oxidase (DAAO) with the signal transduction and amplification of CdS/CNTs-enhanced ECL emission. During DAAO-catalyzed enantioselective-oxidations of alanine, the O₂ is converted to H₂O₂, which tunes the ROS generation. With synergetic regulations of ROS generation by nano-derived CdS/CNTs and bio-derived DAAO, alanine enantiomers are highly discriminated and the L-alanine is quantitatively detected with the most competitive detection limit so far (0.014 fM).