Amplified impedimetric aptasensor based on gold nanoparticles covalently bound graphene sheet for the picomolar detection of ochratoxin A

• AuNPs–rGO was fabricated to provide vast binding sites for DNA strands.
• A sandwich aptasensor was designed with AuNPs–rGO as signal amplification platform.
• 7∼ orders of magnitude in Rct was obtained compared with the AuNPs–rGO absence one.
• The impedimetric aptasensor could detect OTA with picomolar sensitivity.
• The sensitivity is 200∼ fold lower than that of most existed aptasensors using EIS.

An amplified electrochemical impedimetric aptasensor for ochratoxin A (OTA) was developed with picomolar sensitivity. A facile route to fabricate gold nanoparticles covalently bound reduced graphene oxide (AuNPs–rGO) resulted in a large number of well-dispersed AuNPs on graphene sheets with tremendous binding sites for DNA, since the single rGO sheet and each AuNP can be loaded with hundreds of DNA strands. An aptasensor with sandwich model was fabricated which involved thiolated capture DNA immobilized on a gold electrode to capture the aptamer, then the sensing interface was incubated with OTA at a desired concentration, followed by AuNPs–rGO functionalized reporter DNA hybridized with the residual aptamers. By exploiting the AuNPs–rGO as an excellent signal amplified platform, a single hybridization event between aptamer and reporter DNA was translated into more than 107 redox events, leading to a substantial increase in charge-transfer resistance (Rct) by 7∼ orders of magnitude compared with that of the free aptamer modified electrode. Such designed aptasensor showed a decreased response of Rct to the increase of OTA concentrations over a wide range of 1 pg mL−1–50 ng mL−1 and could detect extremely low OTA concentration, namely, 0.3 pg mL−1 or 0.74 pM, which was much lower than that of most other existed impedimetric aptasensors. The signal amplification platform presented here would provide a promising model for the aptamer-based detection with a direct impedimetric method.

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