RuSiNPs@N,S-GQDs as self-enhanced anodic electrochemiluminescent immunobeacons for the highly sensitive quantitation of okadaic acid in shellfish

A competitive electrochemiluminescence (ECL) immunosensor is proposed to accurately and rapidly assess okadaic acid (OA) levels in shellfish using a novel self-reinforced solid-state ECL marker, which is essential for ensuring seafood safety. Graphene quantum dots doped with nitrogen and sulfur (N,S-GQDs) were synthesized, for the first time, through the electrolysis of graphite in 3-(N-morpholine) propane sulfonic acid solution. Intriguingly, these N,S-GQDs exhibited exceptional co-reactant properties, significantly enhancing the anodic ECL performance of Ru(bpy)₃²⁺ in a phosphate-buffered saline solution. Following the functionalization of Ru(bpy)₃²⁺-doped silica nanoparticles (RuSiNPs) with poly(diallyldimethylammonium) chloride, we achieved a well-dispersed assembly of N,S-GQDs on the exterior of the RuSiNPs through electrostatic interactions. Importantly, the core–shell structure of RuSiNPs@N,S-GQDs efficiently encapsulated both the luminophore and co-reactant, thus improving the transfer rates of electrons, shorting interaction distances, and reducing energy loss during light emission. Leveraging this “bright” ECL beacon, the ECL immunosensor demonstrated remarkable analytical performance, yielding a low half maximal inhibitory concentration (IC₅₀) of 0.14 ng mL⁻¹, an extensive linear range spanning 0.003–40 ng mL⁻¹, and impressively low limit of detection of 0.001 ng mL⁻¹ for OA determination.