A label-free electrochemical aptasensor based on the catalysis of manganese porphyrins for detection of thrombin.

A novel manganese porphyrin (MnPP)-catalyzed aerobic oxidation of l-cysteine to disulfides (RSSR) was firstly found and applied into electrochemical aptasensor with a label-free technique for signal amplification. The possible catalytic mechanism of the catalytic reaction where MnPP catalyzed l-cysteine with thiol (RSH) structure to RSSR was discussed in detail. For fabrication of the aptasensor, thionine (Thi), which served as an electron mediator, was mixed with MnPP and immobilized on the nafion coated carbon electrode through ion exchange adsorption. Gold nanoparticle (nano-Au) was assembled on the Thi for immobilizing thrombin binding aptamer (TBA). In the presence of thrombin (TB), TBA will capture TB and form TBA-TB composite thus perturbed electron transfer, leading to decrease of the current for quantitatively detecting TB. Under optimal condition, the electrochemical aptasensor exhibited a linear range of 0.1-25nM with a detection limit of 0.02nM. This work opens a novel way for signal amplification study about porphyrins that served as mimetic enzyme to thiol in electrochemical aptasensor.