Regulation of Ru(bpy) Electrochemiluminescence Based on Distance-Dependent Electron Transfer of Ferrocene for Dual-Signal Readout Detection of Aflatoxin B1 with High Sensitivity.

Ferrocene (Fc) is a common quencher of Ru(bpy) luminescence. However, interactions between Fc and Ru(bpy) can be extremely complicated. In this work, we reported the first use of Fc to regulate the electrochemiluminescence (ECL) of Ru(bpy) by tuning the length of the DNA sequence between Fc and the luminophore of nitrogen-doped graphene quantum dots-Ru(bpy)-doped silica nanoparticles (SiO@Ru-NGQDs). The ECL of SiO@Ru-NGQDs was depressed when the distance between Ru(bpy) and Fc was less than 8 nm; a stronger ECL was observed when the distance was more than 12 nm. The switching of the ECL of Ru(bpy) by Fc was attributed to the electron transfer mechanism, in which Fc participated in the redox of Ru(bpy) for "signal-off" ECL; this favored electron transfer at the electrode fabricated with an Fc-labeled aptamer (Fc-apt) and SiO@Ru-NGQDs for "signal-on" ECL depending on the length of the DNA sequence. Here, a dual-signal readout aptasensor for aflatoxin B1 (AFB1) detection was developed via the enhanced ECL of SiO@Ru-NGQDs by Fc-apt. The redox currents of Fc and the ECL of Ru(bpy) were simultaneously collected as yardsticks, and both decreased with higher concentrations of AFB1. The aptasensor allowed linear ranges of 3 × 10 to 1 × 10 ng mL for ECL mode and 1 × 10 to 3 × 10 ng mL for electrochemical mode. Our work provides insight into the interactions between Fc and Ru(bpy). The dual-signal readout strategy is a potential platform for the versatile design of aptasensors.