High-Entropy Single-Atom Catalyst as Coreactant Accelerator for Reactive Oxygen Species-Mediated Electrochemiluminescence

Single-atom catalysts (SACs) have garnered significant attention as coreactant accelerators in luminol-dissolved O₂ electrochemiluminescence (ECL) systems, but designing and fabricating highly efficient SACs remain a critical challenge. In this study, we present the first attempt to develop a high-entropy single-atom catalyst (HE-SAC) by rationally and atomically modulating multiple isolated heteroatom active sites (Fe, Co, Cu, Ni, and Mn) in M-N₄ coordination moieties within pyridinic and pyrrolic nitrogen-rich graphitic frameworks. This HE-SAC features a square-planar geometric structure with low symmetry and a highly localized electron distribution, leading to enhanced catalytic activity for reactive oxygen species (ROS) generation and, consequently, improved luminol ECL performance. Synchrotron radiation analysis and density functional theory (DFT) calculations indicate that Mn-N₄ and Co-N₄ function as electron delocalizers to modulate the catalytic activity of Fe sites during O₂ activation, while Ni-N₄ and Cu-N₄ promote weak binding with intermediates. The unique electronic structure and synergistic interaction among the HE-SAC metal active sites enhance the catalytic activity, boosting ROS production. The interactions between active sites and the graphenic support leverage high entropy to further boost the HE-SAC durability and catalytic efficiency. Furthermore, the incorporation of luminol-modified AgNPs with HE-SAC significantly enhances the ECL signal, resulting in a 5.9-fold increase compared with single Fe-SAC under optimal conditions, strongly aligning with theoretical DFT prediction. As a proof of concept, the acquired ECL biosensor was fruitfully applied to the ultrasensitive detection of miRNA-21. The regulation of high-entropy single heteroatoms offers a pioneering approach to accelerate intermediate generation for boosting coreactant ECL systems.