Toward mechanistic understanding of electrochemiluminescence generation by tris(2,2′-bipyridyl)ruthenium(II) and peroxydisulfate

Electrochemiluminescence (ECL) generation by tris(2,2’-bipyridyl)ruthenium (Ru(bpy) 3 2+ ) and S 2 O 8 2− is one of most frequently studied cathodic systems. However, the reaction mechanism is yet to be fully resolved, since the reaction involving highly reactive intermediates occurs at the negative potential limit of aqueous solutions. In this work we used bismuth microwire (BiMW) as the working electrode and ECL microscopy (ECLM) as the imaging tool to study the mechanism of cathodic ECL generation by Ru(bpy) 3 2+ /S 2 O 8 2− . Thanks to its high hydrogen evolution overpotential, BiMW electrode could provide us with a wide negative potential window in aqueous solutions. While ECLM allowed us to determine the thickness of ECL layer (TEL), which was found to vary from ca. 3.4 μm to 3.0 μm with increasing the concentration of S 2 O 8 2− . Given the chemical reduction of S 2 O 8 2− by Ru(bpy) 3 + is essential for extending the concentration profile of SO 4 •− , the slightly changed TEL is likely related to the instability of Ru(bpy) 3 + in aqueous solutions. Finally, no ECL was detected for Ru(bpy) 3 2+ -labelled microbeads, implying that S 2 O 8 2− could not work as the cathodic coreactant like tri- n -propylamine (TPrA) as the anodic one in bead-based immunoassays .