Copper-Deficient Cu_2–<i>x</i>Se/g-C₃N₄ Immobilizing Lactate Oxidase Cascade Catalytic Chemiluminescence for Lactate Detection

Integrating distinct catalytic processes to develop novel cascade catalytic systems, thereby enhancing catalytic efficiency, holds significant promise for biosensing applications, owing to its superior advantages in signal transduction and amplification. Herein, we constructed an integrated enzyme and copper-deficient semiconductor heterojunction system by immobilizing lactate oxidase (LOx) onto Cu_2-<i>x</i>Se/g-C₃N₄ (denoted as Cu_2-<i>x</i>Se/g-C₃N₄-LOx) to enable cascade-catalyzed chemiluminescence (CL) for the sensitive detection of lactate (LA). The Cu_2-<i>x</i>Se/g-C₃N₄ heterojunction was fabricated via electrostatic self-assembly of copper-deficient Cu_2-<i>x</i>Se nanoparticles and graphitic carbon nitride (g-C₃N₄) nanosheets. The nanocomplex exhibited enhanced catalytic activity owing to efficient carrier transfer, which promoted the generation of reactive oxygen species (ROS). The immobilized LOx converted LA into H₂O₂, which was subsequently catalyzed by Cu_2-<i>x</i>Se/g-C₃N₄ in the presence of luminol, generating enhanced CL signals for the rapid and sensitive detection of LA. The system achieved a linear detection range of 0.01-200 μmol/L and a limit of detection (LOD) of 6.86 nmol/L for LA. Furthermore, the Cu_2-<i>x</i>Se/g-C₃N₄-LOx cascade catalytic system was successfully applied to quantify LA in human serum samples. Notably, LA levels in lung cancer patients were significantly higher than in healthy individuals, suggesting its potential as a diagnostic biomarker for lung cancer.