Construction of Codirectional Charge Transfer Channels in Imine-Linked Covalent Organic Frameworks with Enhanced Electrochemiluminescence for Ultrasensitive Lincomycin Assay

Covalent organic frameworks (COFs) have garnered increasing attention in electrochemiluminescence (ECL), but how to improve ECL efficiency is still challenging due to the insufficient charge separation driving forces and non-directional charge transfer. Herein, by rationally modulating the types of building blocks, we synthesize two donor−acceptor (D−A) imine-linked COFs with distinct charge transfer directionality (namely Btt-Tpa-COF and Btt-Tapt-COF). In Btt-Tapt-COF, the D−A orientations of building units align with those of imine bonds (C δ+ =N δ− ), which facilitates the establishment of codirectional charge transfer channels and significantly promotes the intramolecular charge separation/transport for the achievement of exceptional ECL performance. In contrast, Btt-Tpa-COF exhibits the reduced ECL stability and efficiency due to its reversed D−A orientation that impedes the intramolecular charge transfer. As a proof of concept, we construct a target-responsive ECL aptasensor to measure lincomycin (LIN) with Btt-Tapt-COF as an efficient emitter and the three-dimensional DNA hydrogel as an intelligent signal switch. This aptasensor can sensitively measure LIN within a large linear response range of 0.0001−10 ng/mL. Importantly, this research reveals the effect of charge transfer directionality on ECL performance and provides a promising strategy for the construction of efficient ECL sensors to quantify antibiotics in food and the environment.