An impedance aptasensing method based on the strep-tag system integrated apta-magnetic probe for acetamiprid determination

Abstract

For electrochemical aptamer analysis based on magnetic beads (MBs), especially for electrochemical impedance analysis, MBs are often directly involved in signal measurements, which may cause high background signals, as well as interference from non-specific adsorption. Herein, a method for the indirect involvement of MBs in impedance aptasensing was developed. The key to this method is the construction of a Strep-Tag system integrated apta-magnetic probe, in which the Strep-tag system was employed as a link between the aptamer and MBs. The acetamiprid-binding aptamer (ABA) was indirectly attached to Strep-Tactin-coated MBs (STMBs), through the hybridization with its complementary strand (cABA), which was covalently conjugated to Strep-tag II. After acetamiprid capture, desthiobiotin triggered the release of Strep-tag II-conjugated cABA, which was subsequently interacted with the ABA-modified electrode for impedance measurements. Moreover, streptavidin-conjugated horseradish peroxidase (streptavidin-HRP) was added to amplify the impedance signal. The changes in electron-transfer resistance (ΔRct) are linearly related to the logarithm of acetamiprid concentration in the range of 0.5–10 pM. Detection limit as low as 0.15 pM was achieved. Satisfactory recoveries ranging from 95.25 to 101.2 % with relative standard deviations of 5.12 % were also obtained in analyzing real spiked agricultural products.