A highly selective and sensitive cocaine aptasensor based on covalent attachment of the aptamer-functionalized AuNPs onto nanocomposite as the support platform

• Functionalized thiol-terminated cocaine aptamer was functionalized with AuNPs.
• MWCNTs/IL/Chit was employed for covalent attachment of Apt-capture probe onto electrode.
• (K3Fe(CN)6) was used as the redox probe and DPV as analytical technique.
• The aptasensor showed high sensitivity and selectivity.
• Linear range from 1 nM to 11,000 nM with LOD of 100 pM for cocaine detection was obtained.

Based on the conformational changes of the aptamer-functionalized gold nanoparticles (AuNPs) onto MWCNTs/IL/Chit nanocomposite as the support platform, we have developed a sensitive and selective electrochemical aptasensor for the detection of cocaine. The 5′-amine-3′-AuNP terminated aptamer is covalently attached to a MWCNTs/IL/Chit nanocomposite. The interaction of cocaine with the aptamer functionalized AuNP caused the aptamer to be folded and the AuNPs with negative charge at the end of the aptamer came to the near of electrode surface therefore, the electron transfer between ferricyanide (K3Fe(CN)6) as redox probe and electrode surface was inhibited. A decreased current of (K3Fe(CN)6) was monitored by differential pulse voltammetry technique. In an optimized condition the calibration curve for cocaine concentration was linear up to 11 μM with detection limit (signal-to-noise ratio of 3) of 100 pM. To test the selectivity of the prepared aptasensor sensing platform applicability, some analgesic drugs as the interferes were examined. The potential of the aptasensor was successfully applied for measuring cocaine concentration in human blood serum. Based on our experiments it can be said that the present method is absolutely beneficial in developing other electrochemical aptasensor.

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