Here, we discovered that rigidifying the tetraphenylethylene (TPE)-based ligand H4TCBPE (H4TCBPE = 1,1,2,2-tetra­(4-carboxylbiphenyl)­ethylene) into Hf-based metal–organic framework (Hf-TCBPE) could lead to a stronger electrochemiluminescence (ECL) emission in comparison to H4TCBPE aggregates and H4TCBPE monomers. Due to the lack of close-packed TCBPE chromophores in Hf-TCBPE, which was required for aggregation-induced ECL (AI-ECL) enhancement, we defined this unprecedented phenomenon as matrix coordination-induced ECL (MCI-ECL) enhancement. The strong ECL intensity of Hf-TCBPE not only originated from the fixation of the TCBPE ligand between Hf6 clusters that restricted the intramolecular free motions of TCBPE and suppressed the nonradiative relaxation but also stemmed from the high porosity of Hf-TCBPE that rendered both internal and external TCBPE chromophores able to be excited. Considering the unique ECL characteristic of Hf-TCBPE, we combined the new ECL indicator of Hf-TCBPE as well as the phosphate-terminal ferrocene (Fc)-labeled hairpin DNA (Fc-HP3) aptamer together as a signal probe (Hf-TCBPE/Fc-HP3), which was employed to construct a novel “off–on” ECL sensor for ultrasensitive mucin 1 (MUC1) detection with the assistance of the exonuclease III (Exo III)-assisted recycling amplification strategy. As expected, the ECL sensor displayed a desirable linear response range from 1 fg/mL to 1 ng/mL and the detection limit down to 0.49 fg/mL. The MCI-ECL enhancement demonstrated by the Hf-TCBPE developed a new and promising strategy to design and synthesize high-performance metal–organic framework (MOF)-based ECL materials for constructing ultrasensitive ECL sensors.

In this work, a novel mesoporous luminescence-functionalized metal-organic framework (Ru-PCN-777) with high stability and excellent electrochemiluminescence (ECL) performance was synthesized by immobilizing Ru(bpy)(mcpbpy) on the Zr cluster of PCN-777 via a strong coordination bond between Zr and -COO. Consequently, the Ru(bpy)(mcpbpy) could not only cover the surface of PCN-777 but also graft into the interior of PCN-777, which greatly increased the loading amount of Ru(bpy)(mcpbpy) and effectively prevented the leaching of the Ru(bpy)(mcpbpy) resulting in a stable and high ECL response. Considering the above merits, we utilized the mesoporous Ru-PCN-777 to construct an ECL immunosensor to detect mucin 1 (MUC1) based on proximity-induced intramolecular DNA strand displacement (PiDSD). The ECL signal was further enhanced by the enzyme-assisted DNA recycling amplification strategy. As expected, the immunosensor had excellent sensitivity, specificity, and responded wide linearly to the concentration of MUC1 from 100 fg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL (S/N = 3). It is the first time that mesoporous Zr-MOF was introduced into ECL system to assay biomolecules, which might expand the application of mesoporous metal-organic frameworks (MOFs) in bioanalysis. This work indicates that the use of highly stable mesoporous luminescence-functionalized MOFs to enhance the ECL intensity and stability is a feasible strategy for designing and constructing high-performance ECL materials, and therefore may shed light on new ways to develop highly sensitive and selective ECL sensors.

In this work, a new strategy was developed to construct high-performance electrochemiluminescent materials by using AIEgen-based ultrathin metal–organic layer to enhance electrochemiluminescence intensity and efficiency.

Metal–organic frameworks (MOFs) with porous structures exhibit favorable promise in synthesizing high-performance electrochemiluminescence (ECL) materials, yet their micropores and narrow channels not only restrict the loading capacity of ECL luminophores but also constrain the diffusion of coreactants, ions, and electrons. Hence, we developed a new and simple hydrothermal etching strategy for the fabrication of a hollow hierarchical MOF (HH-UiO-66-NH2) with a hierarchical-pore shell, which was employed as a carrier to graft Ru­(bpy)2(mcpbpy)2+ (bpy = 2,2′-bipyridine, mcpbpy = 4-(4′-methyl-[2,2′-bipyridin]-4-yl) butanoic acid) onto the coordinatively unsaturated Zr6 nodes of HH-UiO-66-NH2, creating the Ru-complex-grafted HH-UiO-66-NH2 (abbreviated as HH-Ru-UiO-66-NH2). Impressively, the HH-Ru-UiO-66-NH2 presented brilliant ECL emission. On the one hand, the HH-UiO-66-NH2 with a hierarchical-pore shell and hollow cavity was conducive to immobilize the Ru­(bpy)2(mcpbpy)2+ of large steric hindrance into the interior of the MOF, markedly improving the load number of luminophores. On the other hand, the hierarchical-pore shell of HH-UiO-66-NH2 permitted fast diffusion of coreactants, ions, and electrons that facilitated the excitation of more grafted luminophores and greatly enhanced the utilization ratio of ECL luminophores. Inspired by the superior ECL performance of HH-Ru-UiO-66-NH2, an ECL sensing platform was constructed on the basis of HH-Ru-UiO-66-NH2 as an ECL beacon combining catalytic hairpin assembly as a signal amplification strategy, showing excellent selectivity and high sensitivity for thrombin determination. This proof-of-concept work proposed a simple and feasible hydrothermal etching strategy to construct hollow hierarchical MOFs that served as carrier materials to immobilize ECL luminophores, providing significant inspiration to develop highly efficient ECL materials and endowing hollow hierarchical MOFs with ECL sensing applications for the first time.