Covalent Bridging Achieves Nanorestriction Enhanced Aggregation-Induced Electrochemiluminescence for 17β-Estradiol ECL Imaging-Assisted Dual-Mode ECL/EC Detection

This study presents a novel dual-mode biosensor that integrates electrochemiluminescence (ECL) and electrochemical (EC) techniques for the ultrasensitive detection of 17β-estradiol (E2). The biosensor system employed 4',4″,4‴,4'‴-(ethene-1,1,2,2-tetrayl)tetrabiphenyl-4-carboxylic acid (TCBPE)-UiO-66-NH₂, synthesized via covalent amide bonding, as the ECL emitter. Covalent bridging of the aggregation-induced emission luminogen (AIEgen) TCBPE onto UiO-66-NH₂ created a nanoconfined environment that suppressed intramolecular motions, reduced nonradiative decay, and thus dramatically enhanced the ECL performance and detection sensitivity. The biosensor platform employs an "on-off-on" sensing strategy based on the ECL resonance energy transfer mechanism. To ensure high sensitivity, the system integrates Mg²⁺-driven DNAzyme walkers for signal amplification. Upon activation, these walkers catalytically cleave the hairpin DNA probes to release methylene blue (MB), thereby effectively restoring the ECL signal. The inherent EC activity of MB enabled simultaneous ECL and EC dual-mode signal output. ECL imaging was used as an auxiliary validation method, visually confirming the correlation between the intensity gradients on the biosensor surface and E2 concentrations. The biosensor demonstrated a broad detection range from 0.01 to 200 ng/mL, with detection limits of 3.27 fg/mL in the ECL mode and 6.76 fg/mL in the EC mode. This work provides a novel dual-mode biosensor strategy combining AIEgen covalent immobilization and DNAzyme amplification, offering an effective approach for E2 monitoring.