A novel label-free cocaine assay based on aptamer-wrapped single-walled carbon nanotubes

Objective(s): This paper describes a selective and sensitive biosensor based on the dissolution and aggregation of aptamer wrapped single-walled carbon nanotubes. We report on the direct detection of aptamer–cocaine interactions, namely between a DNA aptamer and cocaine molecules based on near-infrared absorption at λ807. Materials and Methods: First a DNA aptamer recognizing cocaine was non-covalently immobilized on the surface of single walled carbon nanotubes and consequently dissolution of SWNTs was occurred. Vis-NIR absorption (A807nm) of dispersed, soluble aptamer-SWNTs hybrid, before and after incubation with cocaine was measured using a CECIL9000 spectrophotometer. Results: This carbon nanotube setup enabled the reliable monitoring of the interaction of cocaine with its cognate aptamer by aggregation of SWNTs in the presence of cocaine. Disscusion: This assay system provides a mean for the label-free, concentration-dependent, and selective detection of cocaine with an observed detection limit of 49.5 nM.