The successful use of electrochemiluminescence (ECL) in immunoassay for clinical diagnosis requires development of novel ECL signal probes. Herein, we report lanthanide (Ln) metal−organic frameworks (LMOFs) as ECL signal emitters in the ECL immunoassay. The LMOFs were prepared from precursors containing Eu (III) ions and 5-boronoisophthalic acid (5-bop), which could be utilized to adjust optical properties. Investigations of ECL emission mechanisms revealed that 5-bop was excited with ultraviolet photons to generate a triplet-state, which then triggered Eu (III) ions for red emission. The electron-deficient boric acid decreased the energy-transfer efficiency from the triplet-state of 5-bop to Eu (III) ions; consequently, both were excited with highefficiency at single excitation. In addition, by progressively tailoring the atomic ratios of Ni/Fe, NiFe composites (Ni/Fe 1:1) were synthesized with more available active sites, enhanced stability, and excellent conductivity. As a result, the self-luminescent europium LMOFs displayed excellent performance characteristics in an ECL immunoassay with a minimum detectable limit of 0.126 pg mL −1 , using Cytokeratins21-1 (cyfra21-1) as the target detection model. The probability of false positive/false negative was reduced dramatically by using LMOFs as signal probes. This proposed strategy provides more possibilities for the application of lanthanide metals in analytical chemistry, especially in the detection of other disease markers.

We have proposed a dual-quenching electrochemiluminescence (ECL) strategy which is based on tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy) 3 2+ ] as chromophores caged in three-dimensional (3D) zinc oxalate metal−organic frameworks [Ru(bpy) 3 2+ /zinc oxalate MOFs] for ultrasensitive detection of amyloid-β (Aβ). The threedimensional chromophore connectivity in zinc oxalate MOFs provided a network for rapid excited-state energy transfer migration among Ru(bpy) 3 2+ units which shielded the chromophores from solvent molecules and led to a high-energy Ru emission efficiency. In addition, we found that both Au nanoparticles and NiFe-based nanocube MOFs could contribute to the reduction of the ECL intensity of the chromophore. The ECL emission spectra of 3D Ru(bpy) 3 2+ /zinc oxalate MOFs overlapped appropriately with the ultraviolet−visible (UV−vis) absorption spectra of Au@NiFe MOFs composites, which could trigger the resonance energy transfer (RET) behavior between Ru(bpy) 3 2+ /zinc oxalate MOFs (donor) and Au@NiFe MOFs (acceptor), achieving the dual-quenching effect of Ru(bpy) 3 2+ encapsulated in 3D zinc oxalate MOFs and significantly boosting the sensitivity of the Aβ detection immunosensor. In order to examine the clinical practicability, we have applied it to verify the content of Aβ solution ranging from 100 fg mL −1 to 50 ng mL −1 and obtained the calibration curve with high correlation coefficient, along with the low limit of detection of 13.8 fg mL −1 . Above all, this work demonstrated an approach of constructing dual-quenching effect ECL immunosensors in whole 3D MOF systems and its application in ECL detection methodology.

This work describes a sandwich-type electrochemiluminescence (ECL) strategy for insulin detection by using Ru(bpy) as the luminophore which was encapsulated in the UiO-67 metal-organic framework (UiO-67/Ru(bpy)). Because UiO-67 possesses the characteristics of large specific surface area and porosity, more Ru(bpy) could be loaded onto its surface and holes, thus greatly improving the ECL efficiency. Furthermore, the ECL resonance energy transfer (ECL-RET) could occur between UiO-67/Ru(bpy) (ECL donor) and Au@SiO nanoparticles (ECL acceptor), resulting in a conspicuously decreased ECL response. The ECL spectrum of UiO-67/Ru(bpy) which exhibited strong ECL intensity has suitable spectral overlap with the absorption spectrum of Au@SiO, which further proved the occurrence of the ECL-RET action. The ECL intensity decreased with the increase of the concentration of insulin. In addition, the sandwich-type ECL immunosensor was applied to insulin detection, and the ECL decrease efficiency was found to be logarithmically related to the concentration of the insulin antigen in the range of 0.0025 to 50 ng mL with the limit of detection of 0.001 ng mL. Meanwhile, this work provides an important reference for the application of metal-organic frameworks in the ECL and ECL-RET study and also exhibits potential capability in the detection of other hormones.

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