A novel redox probe 3,4,9,10-perylenetetracarboxylic acid/o-phenylenediamine (PTCA/OPD) with well-defined redox peaks caused by the synergistic action between them was demonstrated via theoretical and practical research, and applied in an electrochemical aptasensor to detect thrombin (TB) based on an Fe₃O₄ magnetic bead (MB) as a nonenzymatic catalyst.