In this work, with the use of Ag(I) ion as robust coreaction accelerator for the enhancement of 3,4,9,10-perylenetetracarboxylic acid-peroxydisulfate (PTCA-S₂O₈^2-) system, a highly sensitive solid-state electrochemiluminescence (ECL)-biosensing platform was successfully designed for the detection of mercury ions (Hg²⁺). Specifically, a long guanine-rich (C-rich) double-stranded DNA (dsDNA) was generated by the target-Hg²⁺-controlled DNA machine that could amplify the ECL signal of the PTCA-S₂O₈^2- system by embedding the Ag(I) ion. Herein, the Ag(I) ion, as a coreaction accelerator, could first react with S₂O₈^2- to produce Ag(II) ion and a sulfate radical anion (SO₄^·-). Then, the accompanying Ag(II) ion could react with H₂O to generate the reactive intermediate species (i.e., hydroxyl radical (OH^·)), which could further accelerate the reduction of S₂O₈^2- to output more SO₄^·-. Moreover, the recycling of the Ag(I) ion and Ag(II) ion was easily achieved by the electrochemical reaction. Therefore, an avalanche-type reaction was triggered to generate massive amounts of SO₄^·-, which could react with the luminophore (PTCA) to achieve an extremely strong ECL signal. The ECL mechanism was investigated by ECL and cycle voltammetry (CV) and by the analysis of the fluorescence (FL), ECL, and electron-paramagnetic-resonance (EPR) spectra. As a result, the proposed solid-state ECL-biosensing platform for Hg²⁺ detection exhibited high sensitivity, with a linear range from 1 × 10^-15 to 1 × 10^-10 M and a detection limit of 3.3 × 10^-16 M. Importantly, this work was the first to utilize a metal ion as a coreaction accelerator and provided a promising approach to improve the sensitivity of target analyses in ECL-biosensing fields.

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