Fluorescent sensing of cocaine based on a structure switching aptamer, gold nanoparticles and graphene oxide.

This study demonstrates a cocaine sensing method employing graphene oxide (GO), gold nanoparticles and a structure switching aptamer, which can fold into a three-way junction in the presence of cocaine. On the observation of gold nanoparticles (Au NPs) induced graphene oxide fluorescence quenching, a structure switching aptamer of cocaine was introduced as the linker between the two parts. Firstly, two fragments of a cocaine aptamer were immobilized covalently onto GO and Au NPs, respectively. Then when the three-way junction formed, the Au NPs were drawn near to the GO surface and induced a fluorescence intensity decrease. The limit of detection was 0.1 μM for cocaine in purified water, and well defined results were also obtained in biological fluids and the specificity experiment, which expands the feasibility of the as-prepared sensor for practical applications.