Porphyrins-mediated interfacial charge modulation to enhance aggregation-induced electrochemiluminescence of iridium complex for ultrasensitive bioassay

Iridium (III) complexes have attracted much attention as electrochemiluminescence (ECL) luminophores, but their inferior ECL efficiency (ΦECL) in the aqueous solutions has impeded further applications. Herein, meso-tetra (4-carboxyphenyl) porphine (TCPP) was developed as interfacial charge mediator to dramatically enhance aggregation-induced electrochemiluminescence (AIECL) of tris (2-phenylpyridine) iridium(Ⅲ) (Ir(ppy)3), thus improving its ΦECL. As an interfacial charge mediator, TCPP can efficiently accelerate the electrooxidation of Ir(ppy)3 through higher hole transport kinetics. Meanwhile, it is found that its rigid structure can suppress the motions of Ir(ppy)3 to elevate radiative transition efficiency in emission process. Thus, a significantly enhanced AIECL was achieved for aggregation-induced emission luminogens (AIEgens) Ir(ppy)3 @TCPP. Compared to monomer Ir(ppy)3, Ir(ppy)3 @TCPP increased ECL efficiency by 18 times. Ir(ppy)3 @TCPP served as AIEgens to construct ECL biosensor for detecting miRNA-126. Strand-displacement amplification (SDA) coupled with rolling-circle amplification (RCA) for improving the conversion efficiency of target miRNA-126. The integration of excellent AIECL characteristics of Ir(ppy)3 @TCPP and outstanding amplification efficiency of SDA-RCA endowed sensing system with high sensitivity. The limit of detection (LOD) was as low as 17 aM. This work creatively exploited interfacial charge modulation as an effective way to enhance AIECL efficiency. The prepared Ir(ppy)3 @TCPP provided much attractive ECL system for bioanalysis.