Impedance Technique-Based Label-Free Electrochemical Aptasensor for Thrombin Using Single-Walled Carbon Nanotubes-Casted Screen-Printed Carbon Electrode.

An impedance technique-based aptasensor for the detection of thrombin was developed using a single-walled carbon nanotube (SWCNT)-modified screen-printed carbon electrode (SPCE). In this work, a thrombin-binding aptamer (TBA) as probe was used for the determination of thrombin, and that was immobilized on SWCNT through π-π interaction. In the presence of thrombin, the TBA on SWCNT binds with target thrombin, and the amount of TBA on the SWCNT surface decreases. The detachment of TBA from SWCNT will be affected by the concentration of thrombin and the remaining TBA on the SWCNT surface can be monitored by electrochemical methods. The TBA-modified SWCNT/SPCE sensing layer was characterized by cyclic voltammetry (CV). For the measurement of thrombin, the change in charge-transfer resistance (Rct) of the sensing interface was investigated using electrochemical impedance spectroscopy (EIS) with a target thrombin and [Fe(CN)6]3- as redox maker. Upon incubation with thrombin, a decrease of Rct change was observed due to the decrease in the repulsive interaction between the redox marker and the electrode surface without any label. A plot of Rct changes vs. the logarithm of thrombin concentration provides the linear detection ranges from 0.1 nM to 1 µM, with a ~0.02 nM detection limit.