Single-Luminophore Ratiometric Electrochemiluminescence Based on Afterglow Emission from Defect-Engineered Carbon Nitride

Ratiometric electrochemiluminescence (ECL) sensing is an effective strategy for improving signal reliability; however, most existing systems rely on dual luminophores or multiple electrochemical processes, which inevitably increase system complexity and compromise signal coherence. Herein, a fundamentally different ratiometric ECL paradigm was established based on a single luminophore capable of simultaneously generating conventional and afterglow ECL emissions. By engineering nitrogen defect-rich carbon nitride with defect electronic states, injected electrons can be temporarily stored during pulsed excitation and gradually released to sustain light emission, even after the applied potential is removed. This afterglow ECL process introduces an intrinsically low-background, time-resolved analytical signal with an identical emissive origin to conventional ECL. Based on the synchronous modulation of these homologous signals, an intrinsically self-referenced ratiometric ECL platform with exceptional stability and ultrahigh sensitivity was constructed. As a proof of concept, the strategy was successfully employed to quantify exosomal microRNA at attomolar levels in complex biological samples. Beyond this specific application, the proposed approach also represents a general single-component ratiometric ECL framework that can be utilized to expand the analytical scope of ECL sensing into the time domain.