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

An intriguing aggregation-induced electrochemiluminescence (AIECL) bioconjugate was fabricated by encapsulating -tris(2-phenylpyridine)iridium(III) complexes [Ir(ppy)] 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) aggregated in the single cavity through both intermolecular π-π-stacking interactions and hydrogen bonds that efficiently restricted the intramolecular motions to trigger the AIECL effect. Compared to monomers, Ir(ppy) aggregates performed 5.3-fold-enhanced ECL emission using tri--propylamine (TPrA) as a coreactant. The fabricated Ir(ppy)@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 and the oxidative Ir(ppy) radicals, a conductive and electroactive substrate of FeN and gold nanoparticle-codecorated reduced graphene oxide (FeN/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.