Aggregation-Induced Electrochemiluminescence Bioconjugates of Apoferritin-Encapsulated Iridium(III) Complexes for Biosensing Application

An intriguing aggregation-induced electrochemiluminescence (AIECL) bioconjugate was fabricated by encapsulating fac-tris(2-phenylpyridine)iridium(III) complexes [Ir(ppy)(3)] in the apoferritin (apoFt) cavity for biosensing application. Based on the unique pH-dependent disassembly/reassembly characteristic of apoFt, approximately 44.3 molecules of Ir(ppy)(3) aggregated in the single cavity through both intermolecular stacking interactions and hydrogen bonds that efficiently restricted the intramolecular motions to trigger the AIECL effect. Compared to monomers, Ir(ppy)(3) aggregates performed 5.3-fold-enhanced ECL emission using tri-n-propylamine (TPrA) as a coreactant. The fabricated Ir(ppy)(3)@apoFt bioconjugate was flexibly labeled with a detection antibody to act as a transducer for the immunosensor construction. To further catalyze the ECL reaction between the reductive TPrA(center dot) and the oxidative Ir(ppy)(3)(+center dot) radicals, a conductive and electroactive substrate of Fe2N and gold nanoparticle-codecorated reduced graphene oxide Fe2N/rGO/Au) was established to incubate the capture antibody. Therefore, a signal on immunosensor was developed for sensitive assay of cytokeratin 19 fragment 21-1 (CYFRA 21-1), in which good linearity ranging from 1 pg/mL to 50 ng/mL with a low detection limit of 0.43 pg/mL (S/N = 3) was obtained. This study shares with an inspiration of using apoFt to design iridium(III)-based AIECL emitters, which will expand more possibilities of organic iridium(III) complexes in establishing innovative ECL immunoassays.

Automated summary

An AIECL bioconjugate was developed by encapsulating Ir(ppy)(3) complexes in apoFt, enhancing ECL emission and enabling sensitive detection of CYFRA 21-1. This study demonstrates the potential for utilizing apoFt in designing iridium(III)-based AIECL emitters for innovative ECL immunoassays.