A label-free electrochemical aptasensor based on magnetic biocomposites with Pb2+-dependent DNAzyme for the detection of thrombin.

Herein, a novel magnetic biocomposite (Fe3O4@Au-S1/S2) was applied to analyze thrombin. The Fe3O4@Au-S1/S2 consisted of Fe3O4@Au nanoparticles (Fe3O4@Au NPs) as carriers for magnetic separation and magnetic field-induced self-assembly, thiolated complementary strand (S1) anchored based on Au-S bond and thrombin binding aptamer (S2) as a recognition element. As a redox indicator, methylene blue (MB) can be adsorbed to DNA anchored on the surface of Fe3O4@Au NPs by electro-static interaction. In the absence of thrombin, MB were adsorbed on double-stranded DNA (S1/S2) which anchored on Fe3O4@Au NPs and a high electrochemical signal of MB was recorded by Differential pulse voltammetry. Conversely, the complementary strand (S1) exposed after thrombin competitively bonded with aptamer. The introduction of Pb2+-dependent DNAzyme (S3) split S1 at specific rA site, resulting in the significantly decreased adsorption capacity of MB. Thus, the thrombin detection could be recorded by monitoring the electrochemical signal reduction of MB through incubation of thrombin with S3. This method exhibited a high sensitivity toward thrombin with a broad linear range from 5 pmol L-1 to 5 nmol L-1 and a limit of detection of 1.8 pmol L-1.