Bioinspired Single-Atom Sites Enable Efficient Oxygen Activation for Switching Anodic/Cathodic Electrochemiluminescence.

Exploring advanced co-reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol-O2 electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O2 activation to switch anodic/cathodic ECL is very challenging. Herein, we report that enzyme-inspired Fe-based single-atom catalysts with axial N/C coordination structures (FeN5, FeN4(C) SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN5 sites prefer to produce highly active hydroxyl radicals and afford direct cathodic luminescence by promoting the cleavage of O-O bonds through N-induced electron redistribution. In contrast, FeN4(C) sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN5 SAC-based immunosensor was constructed for the sensitive detection of cancer biomarkers.