Dual-Quenching Effects of Methylene Blue on the Luminophore and Co-Reactant: Application for Electrochemiluminescent-Electrochemical Ratiometric Zearalenone Detection

Methylene blue (MB) is a common multifunctional indicator, which can be applied as a quencher for electrochemiluminescence (ECL) analysis as well as a classical redox probe. Although it is relatively prevalent for MB to study the mechanism with Ru-based luminophores in ECL systems, there are few studies on the effects between MB and co-reactants. In this work, we proposed the first investigation of MB on the luminophore and co-reactant of the self-enhanced ECL composites (nitrogen-doped graphene quantum dots on Ru(bpy)32+-doped silica nanoparticles, NGQDs-Ru@SiO2), respectively. The relatively narrow ECL spectrum of luminophore (Ru@SiO2) and the suitable ultraviolet–visible absorption spectrum of MB led to the ECL resonance energy transfer between them, meanwhile the appropriate energy levels among them facilitated the electron transfer, resulting in a decreased ECL signal (quench mode I). Additionally, the co-reactant (NGQDs) was prone to π-π conjugation with MB due to its abundant π-electrons, which reduced the concentration of NGQDs’ intermediates and triggered a weakened ECL signal (quench mode II). Therefore, the dual-quenching effects are ingeniously integrated and designed in one ECL-electrochemical (ECL-EC) ratiometric aptasensor for zearalenone detection, for demonstrating its efficacy in enhancing the sensitivity, which is 4.8-fold higher than Ru@SiO2 alone. This innovative ratiometric aptasensor achieved a relatively wide linear range from 1.0 × 10−15 to 5.0 × 10−8 g mL−1, and obtained a low detection limit of 8.5 × 10−16 g mL−1. Our proposed dual-quenching interactions between MB and NGQDs-Ru@SiO2 will open a new prospective for ECL-EC ratiometric aptasensor, which further broaden the application in sensitive and precise analysis of mycotoxins.