Narrow-Window Cathodic Electrochemiluminescence from Laser-Engineered Graphitic Carbon Nitride: A Next-Generation Emitter for Microplastics Biosensing

The accuracy of anode electrochemiluminescence (ECL)-based microplastic detection in seawater is undermined by ubiquitous reducing agents. These substances quench the signal by both competing for electrons with the emitter and coreactant to limit critical intermediate generation and directly deactivating the excited species via electron transfer, which induces nonradiative decay. In contrast, the cathode ECL system is free from such interference but is susceptible to the hydrogen evolution reaction and subsequent passivation inactivation of the emitter under a broad potential window. In this work, a surface-state-mediated band gap emission cathodic ECL emitter is introduced for the first time, synthesized via a laser irradiation to fabricate nitrogen vacancy-enriched graphitic carbon nitride (g-C₃N₄). A unique ECL emission mechanism is exhibited within a narrow potential window, where electron-filled holes react with sulfate radicals to release sufficient energy for triggering intrinsic electron transition. A poly(vinyl chloride) (PVC) microplastics sensor using as-purposed g-C₃N₄ as emitter was developed, achieving accurate quantification within a concentration range of 0.20 ng/mL to 0.20 μg/mL. Satisfactory sensitivity was enabled via rolling circle amplification strategy assisted by the trans-cleavage activity of CRISPR/Cas12a. The study addresses a critical gap in current microplastic detection technologies and offers an original strategy for rationally designing and constructing novel ECL luminophors.