Discovery of a new coreactant for highly efficient and reliable electrochemiluminescence

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Using luminophore and coreactant pairs increases light emission in electrochemiluminescence (ECL) reactions, improving the overall sensitivity of ECL assays. The most commonly used coreactant is tri- n -propylamine (TPrA) for its capability as a reducing agent. However, TPrA is hydrophobic and readily oxidized, which limits its utility in biosensing. Here, we report the discovery and characterization of the new coreactant 4-(dimethylamino)pyridine (4-DMAP). The compound is highly water soluble and chemically stable under ambient conditions. Most importantly, 4-DMAP generated ECL signals >180 times higher than TPrA in tris(bipyridine)ruthenium(II) [Ru(bpy) 3 ] 2+ . The 4-DMAP ECL enabled ultra-sensitive and robust immunoassays. For example, the 4-DMAP ECL reliably detected protein markers in extracellular vesicles from the plasma samples of cancer patients. It also achieved >200-fold higher sensitivity than TPrA-ECL did in quantifying neutralizing antibodies against SARS-CoV-2 in human saliva. These findings could lead to exciting new opportunities for using ECL-based sensing in a range of clinical applications. • 4-DMAP is a potent alternative to TPrA, generating 180-fold stronger ECL intensities • It is highly water soluble and chemically stable at room temperature • 4-DMAP excites oxidized luminophores through a radical process • The [Ru(bpy) 3 ] 2+ /4-DMAP system enabled highly sensitive detection of biomarkers The sensitivity of electrochemiluminescence (ECL) assays relies on effective luminophore-coreactant pairs. Cho et al. introduce 4-(dimethylamino)pyridine (4-DMAP), a stable, water-soluble coreactant that enhances [Ru(bpy) 3 ] 2+ ECL by over 180-fold compared to tri- n -propylamine (TPrA), providing strong signal amplification and versatile biosensing performance in aqueous diagnostic applications.