Fig. 5.

Schematic representation of an electrochemical-based aptasensor. A) Anti-thrombin aptasensor as an anchor sequence immobilized on a gold electrode and a recognition sequence hybridized (A₁). In the presence of ATP, the recognition sequence separates and the EIS signal reduces (A₂). In contrast, in the presence of thrombin, the recognition sequence remains attached to the anchor and the thrombin causes an increase in EIS signal because of blocking the surface of electrode (A₃). In the presence of both targets, aptasensor behaves differently (A₄). B) A QD-based sandwich array. Aptamers specific to thrombin and lysozyme are immobilized on the electrode surface and conjugated by QD-tagged thrombin and lysozyme, respectively (B₁). In the presence of naked targets, QD-tagged targets are released to the environment (B₂) and can be measured via electrochemical methods (B₃). For detailed information, reader is referred to a study conducted by Wang and coworkers.⁷⁶ Note: not drawn to scale.