A novel electrochemical aptasensor based on single-walled carbon nanotubes, gold electrode and complimentary strand of aptamer for ultrasensitive detection of cocaine

Cocaine is a strong central nervous system stimulant and one of the most commonly abused drugs. In this study, an electrochemical aptasensor was designed for sensitive and selective detection of cocaine, based on single-walled carbon nanotubes (SWNTs), gold electrode and complimentary strand of aptamer (CS). This electrochemical aptasensor inherits properties of SWNTs and gold such as large surface area and high electrochemical conductivity, as well as high affinity and selectivity of aptamer toward its target and the stronger interaction of SWNTs with single-stranded DNA (ssDNA) than double-stranded DNA (dsDNA). In the absence of cocaine, a little amount of SWNTs bind to Aptamer-CS-modified electrode, so that the electrochemical signal is weak. In the presence of cocaine, aptamer binds to cocaine, leaves the surface of electrode. So that, a large amount of SWNTs bind to CS-modified electrode, generating to a strong electrochemical signal. The designed electrochemical aptasensor showed good selectivity toward cocaine with a limit of detection (LOD) as low as 105 pM. Moreover, the fabricated electrochemical aptasensor was successfully applied to detect cocaine in serum with a LOD as low as 136 pM.