Electrochemical aptameric sensor based on the Klenow fragment polymerase reaction for cocaine detection.

An electrochemical aptasensor based on Klenow fragment (KF) polymerase reaction that combines the aggregation of ferrocene-functionalized oligonucleotide has been developed successfully for cocaine detection. In the presence of cocaine, the recognition probe changed its hairpin conformation into the tripartite complex. The aptamer-cocaine complex gave a 3'-single-stranded tail sequence complementary to the surface-tethered capture probe. In KF polymerase reaction, the recognition probe served as a template for the extension of a capture probe. It requires a sample volume of 2 μL and is complete within 1 h. The ferrocene-appended oligonucleotide incorporated into the newly synthesized complementary probe leads to an electrochemical response. This sensitive detection of cocaine is due to a very low background signal and large signal enhancement up to 9-fold upon addition of analyte. It permits detection of as low as 200 μM cocaine. The simple and isothermal procedure does not require thermal cycling or special laboratory conditions, which makes it adaptable to low-cost and robust biosensing.