Electrochemiluminescence quenching via capture of ferrocene-labeled ligand-bound aptamer molecular beacon for ultrasensitive detection of thrombin

Herein, we present an ultrasensitive protein-detection protocol based on electrochemiluminescence (ECL) quenching through capture of ferrocene-labeled ligand-bound aptamer molecular beacon (MB). Our device included two main parts: a solid-state ECL sensing platform and an ECL switch. The sensing platform was constructed by modifying the composite of tris(2,2′-bipyridyl) ruthenium(II) and platinum nanoparticles (Ru-PtNPs) and followed by immobilization of capture DNA (CaDNA). MB worked as the ECL intensity switch. In the presence of thrombin (TB), the hairpin-shaped MB binded to TB, inducing the exposure of a partial single-strand (MBs at this state was ligand-bound MBs). The exposed single stand was complementary to CaDNA and hybridized with CaDNA, leading to the capture of ligand-bound MB onto ECL sensing platform and finally resulting in ECL quenching by ferrocene that linked to MB. Otherwise, the ligand-unbound MB could not be captured and ECL quenching would not happen. Accordingly, the change of ECL intensity indirectly reflected the concentration of TB in the sample. The results indicated that our protocol realized recognition of TB directly in the solution and exhibited much higher sensitivity with a detection limit of 1.7 pM. Thus, this approach would be a promising protein-detection procedure directly performed in the solution.