Label-Free Electrochemical Strategy for Probing TdT and Exo I Activity by Silver-Based Square Wave Voltammetry

Monitoring DNA-related enzymes activity precisely and reliably is absolutely vital to better grasp their roles in the initiation and progression of cancer, thus further exploring their functions in cancer diagnosis and treat. Here, we establish a label-free electrochemical biosensor for investigating both terminal deoxynucleotidyl transferase (TdT) and exonuclease I (Exo I) activity by silver-based square wave stripping voltammetry (SWV). The strategy is achieved by two attractive points in design: a TdT-derived enzymatic synthesis of randomly arrayed C-rich DNA sequence and an Exo I-guided enzymatic degradation. This C-rich DNA-templated silver nanoclusters (AgNCs) serve as the electrochemical signal probe, and a signal on-off modulated process is displayed for the existence of TdT and Exo I, respectively. On account of AgNCs-based square wave stripping voltammetry, testing TdT has a linear concentration range of 0.001 to 5 U/mL with a detection limit of 0.00044 U/mL (S/N = 3). Additionally, Exo I with a detection limit of 0.027 U/mL (S/N = 3) can be analyzed with a linear range of 0.1 to 500 U/mL. The real application of the proposed method in their inhibitors screening is also discussed well. The biosensor provides a powerful idea for the ultrasensitive bio-analysis and shows broad clinical application prospect.