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

The accurate and rapid assessment of okadaic acid (OA) levels in shellfish is of paramount importance for ensuring seafood safety. In this study, a competitive electrochemiluminescence (ECL) immunosensor was proposed for the precise quantitation of OA, utilizing a novel self-enhanced solid-state ECL marker. Graphene quantum dots doped with nitrogen and sulfur ( N,S -GQDs) were synthesized through the electrolysis of graphite in 3-( N -morpholine) propane sulfonic acid (MOPS) solution. Intriguingly, these N,S -GQDs exhibited exceptional co-reactant properties, significantly enhancing the anodic ECL performance of Ru(bpy) ₃ ²⁺ in a phosphate-buffered saline solution. Following the functionalization of Ru(bpy) ₃ ²⁺ -doped silica nanoparticles (RuSiNPs) with poly(diallyldimethylammonium) chloride (PDDA), 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, facilitating improved electron transfer rates, shorter interaction distances, and reduced energy loss during light emission. Consequently, the RuSiNPs@ N,S -GQDs displayed enhanced ECL properties compared to bare RuSiNPs. Leveraging this "bright" ECL beacon, our ECL immunosensor demonstrated remarkable analytical performance, yielding a low half maximal inhibitory concentration (IC ₅₀ ) of 0.14 ng mL ^− 1 , an extensive linear range spanning 0.003-40 ng mL ^− 1 , and impressively low limit of detection of 1 fg mL ^− 1 for OA determination.