A novel biosensing platform based on the Ag(i) ion-enhanced or Ag nanocluster (NC)-quenched electrochemiluminescence (ECL) of CdSe quantum dots (QDs) was designed for versatile "on-off" assays of thrombin (TB) and miRNA, in which bipedal molecular machine (BMM)-triggered surface programmatic chain reaction (SPCR) coupled with mesoporous silica nanoparticle (MSN) multiple amplification is used to introduce plentiful QDs and Ag+ ions to significantly improve the ECL signal.