Ultrasensitive cathodic electrochemiluminescence immunoassay for C-reactive protein enabled by boron-doped diamond...

The advancement of ultrasensitive cathodic electrochemiluminescence (ECL) immunoassays is frequently limited by slow electron transfer kinetics during coreactant reduction and significant interference from hydrogen evolution on conventional electrode materials. To overcome these challenges, we developed a novel immunosensor for C-reactive protein (CRP) that integrates the exceptional electrochemical properties of in-house fabricated boron-doped diamond (BDD) electrodes with the strong luminescence of quantum dot nanospheres (QDNs). Mechanistic studies demonstrate that the BDD surface markedly accelerates the reduction kinetics of the peroxydisulfate coreactant compared to glassy carbon electrodes. This efficient electron injection facilitates the generation of abundant sulfate radical anions, resulting in an earlier onset potential and a ∼5-fold enhancement in cathodic ECL intensity. By coupling the QDNs/S₂O₈^2-/BDD-driven ECL enhancement strategy with magnetic pre-concentration of the target protein, the proposed sensor delivers exceptional analytical performance, achieving an ultralow limit of detection (LOD) of 218 fg/mL and an ultra-wide linear dynamic range covering 8 orders of magnitude (350 fg/mL to 35 μg/mL). Furthermore, the present method demonstrates superior analytical performance in complex serum matrices in contrast with commercial chemiluminescent immunoassays. This study not only provides deep insights into the ECL behavior of QDNs/K₂S₂O₈ on BDD electrodes but also highlights its promising potential for clinical diagnostics.