An electrochemical aptasensor for detection of thrombin based on target protein-induced strand displacement

A sensitive electrochemical aptasensor for detection of thrombin based on target protein-induced strand displacement is presented. For this proposed aptasensor, dsDNA which was prepared by the hybridization reaction of the immobilized probe ssDNA (IP) containing thiol group and thrombin aptamer base sequence was initially immobilized on the Au electrode by self-assembling via Au-S bind, and a single DNA labeled with CdS nanoparticles (DP-CdS) was used as a detection probe. When the so prepared dsDNA modified Au electrode was immersed into a solution containing target protein and DP-CdS, the aptamer in the dsDNA preferred to form G-quarter structure with the present target protein resulting that the dsDNA sequence released one single strand and returned to IP strand which consequently hybridized with DP-CdS. After dissolving the captured CdS particles from the electrode, a mercury-film electrode was used for electrochemical detection of these Cd²⁺ ions which offered sensitive electrochemical signal transduction. The peak current of Cd²⁺ ions had a good linear relationship with the thrombin concentration in the range of 2.3 × 10^-9- 2.3 × 10^-12 mol/L and the detection limit was 4.3 × 10^-13 mol/L of thrombin. The detection was also specific for thrombin without being affected by the coexistence of other proteins, such as BSA and lysozyme.