Ruthenium(II) complex-grafted conductive metal-organic frameworks with conductivity- and confinement-enhanced electrochemiluminescence for ultrasensitive biosensing application.

Improving the electrochemiluminescence (ECL) performance of luminophores is an ongoing research hotspot in the ECL realm. Herein, a high-performance metal-organic framework (MOF)-based ECL material (Ru@Ni(HITP), HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with conductivity- and confinement-enhanced ECL was successfully constructed by using conductive MOF Ni(HITP) as the carrier to graft Ru(bpydc) (Hbpydc = 2,2'-bipyridine-4,4'-dicarboxylic acid) into the channels of Ni(HITP). Compared to Ru@Cu(HITP) and Ru@Co(HITP) with relatively low conductivity, the ECL intensity of Ru@Ni(HITP) was prominently increased about 6.76 times and 18.8 times, respectively, which demonstrated that the increase in conductivity induced the ECL enhancement of the MOF-based ECL materials. What's more, the hydrophobic and porous Ni(HITP) can not only effectively enrich the lipophilic tripropylamine (TPrA) coreactants in its channels to enhance the electrochemical oxidation efficiency of TPrA, but also provide a conductive reaction micro-environment to boost the ECL reaction between Ru(bpydc) intermediates and TPrA in confined spaces, thus realizing a remarkable confinement-enhanced ECL. Considering the excellent ECL performance of Ru@Ni(HITP), an ultrasensitive ECL biosensor was prepared based on the Ru@Ni(HITP) ECL indicator combining an exonuclease I-aided target cycling amplification strategy for thrombin determination. The constructed ECL biosensor showcased a wide linear range from 1 fM to 1 nM with a low detection limit of 0.62 fM. Overall, the conductivity- and confinement-enhanced ECL based on Ru@Ni(HITP) provided effective and feasible strategies to enhance ECL performance, which paved a promising avenue for exploring high-efficient MOF-based ECL materials and thus broadened the application scope of conductive MOFs.