Metal–organic frameworks (MOFs) as crystalline materials have been extensively applied in various fields, such as catalysis, sensing, and biomedical applications. However, the applications of MOF materials are limited in electrochemical biosensing owing to their poor conductivity. One effective approach to overcome this obstacle is to introduce the conductive substance into a single MOF nanostructure by incorporating metal nanoparticles or carbon-based nanomaterials into the framework, and coordinating functional molecular components on the framework. Alternatively, by taking advantage of their synthetic tunability and structural regularity, MOFs can be constructed with electroactive linkers, such as metal–porphyrin and ruthenium complexes.
To realize the precise functionalization of MOF nanoprobes, Lei’s group developed a stepwise growth method to encapsulate a black phosphorus quantum dot and catalase into the inner and outer layers of MOFs, respectively. The integrated MOF system as a tandem catalyst could enhance therapeutic effect against hypoxic tumor cells (Angew. Chem., Int. Ed. 2019, 58, 7808-7812). On the basis of the above work, an electroactive MOF (E-MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E-MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E-MOFs demonstrate excellent performance with surface state model in both co-reactant and annihilation ECL in aqueous medium (Figure 1). Compared with the individual components, E-MOFs significantly improve the ECL emission due to the framework structure. The self-enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre-reduction electrolysis. The self-enhanced mechanism is theoretically identified by DFT. The mixed-ligand E-MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.
Figure 1. Single-crystal structure of E-MOF and mechanism of self-enhanced ECL via the accumulation of E-MOF cation radicals.
This work was published as VIP paper inAngewandte Chemie 2020, DOI: 10.1002/anie.202002713 (https://onlinelibrary.wiley.com/doi/full/10.1002/anie.202002713).
The first author of the research work is Jin Zhongchao, a master of our college in Professor Lei’s group. The theoretical part was completed in cooperation with Professor Li Yafei of Nanjing Normal University. The research project received the great support from Professor Ju Huangxian, and was funded by the NSFC and the National Key Technologies R&D Program.