MnO₂ Nanosheet/Polydopamine Double-Quenching Ru(bpy)₃²⁺@TMU-3 Electrochemiluminescence for Ultrasensitive Immunosensing of Alpha-Fetoprotein

In this work, we propose a novel double-quenching electrochemical luminescence (ECL) strategy; this strategy is based on the double-quenching effect of Ru(bpy)32+-functionalized three-dimensional (3D) metal–organic framework (MOF) by MnO2/PDA. An ECL immunosensor for ultrasensitive detection of alpha-fetoprotein (AFP) has been designed. TMU-3 with a rich mesoporous structure can be used to encapsulate Ru(bpy)32+, which can effectively reduce the leakage of Ru(bpy)32+. Moreover, the ultraviolet–visible (UV–vis) absorption spectrum of the lamellar MnO2/PDA nanomaterials with a nanometer scale of about 1 μm overlaps with the ECL emission spectrum of the porous bamboo leaf-like Ru(bpy)32+@TMU-3 with a nanometer scale of about 1 μm. Thus, an ECL resonance energy transfer (ECL-RET) mechanism between Ru(bpy)32+@TMU-3 (donor) and MnO2/PDA (recipient) is formed. In this way, an ECL immunosensor with a dual-quenching strategy for ECL signal is developed. In order to test the practicability of this method in clinical analysis, the detection target marker AFP content ranged from 0.01 pg/mL to 5 ng/mL and the detection limit was set to 10.7 fg/mL. In summary, this work demonstrates the detection and application of a signal-quenched ECL immunosensor and ECL immunoassay based on a luminescence-functionalized MOF system for biomarker detection. It indicates a great prospect in the analysis of other biomarkers and clinical analysis.