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A novel electrochemiluminescence (ECL) biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide (AgNCs@MoS2) as an ECL material, peroxodisulfate (S2O82−) as a co-reactant, and semicarbazide (Sem) as a co-reaction accelerator. Firstly, hairpin probe Ha modified on AgNCs@MoS2/GCE was unfolded based on its hybridization with target microRNA. Then, the unfolded Ha can further be hybridized with another hairpin DNA of Hb on (AuNPs-semicarbazide)@Cu-MOF, resulting in the release of target microRNA, which further causes a cyclic hybridization. This creates more (AuNPs-semicarbazide)@Cu-MOF on the electrode surface, achieving cyclic hybridization signal amplification. Strikingly, due to the presence of Sem, accelerating the reduction of S2O82− and resulting in the generation of more oxidant intermediates of SO42−, the amount of excited states of Agincreases to further amplify the ECL signal. The biosensor exhibited high sensitivity with a low LOD of 1.067 fM, indicating that the introduction of co-reaction accelerators can provide an effective method for signal amplification. The applicability of this method was assessed by investigating the effect of Pb(II) ion on miRNA-162a expression level in maize seedling leaves. [ABSTRACT FROM AUTHOR]