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

Abstract Exploring advanced co‐reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol‐O 2 electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O 2 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 (FeN 5 , FeN 4 © SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN 5 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, FeN 4 © sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN 5 SAC‐based immunosensor was constructed for the sensitive detection of cancer biomarkers.