A nanoporous gold-based electrochemical aptasensor for sensitive detection of cocaine

The increasing application of aptamers in bioassays has triggered a lot of research interest for development of highly sensitive and selective sensing platforms. Herein, we report on the design of a sensitive cocaine biosensor by immobilizing the 5′-disulfide-functionalized end of an aptamer sequence on a nanoporous gold (NPG) electrode followed by the conjugation of its 3′-amino-functionalized end to 2,5-dihydroxybenzoic acid (DHBA) as the redox probe. In the presence of cocaine, the aptamer undergoes a conformational change from an open unfolded state to a closed conformation, which reduces the distance between DHBA and the electrode surface, resulting in the enhanced electron-transfer efficiency. Using square wave voltammetric method and under the optimal conditions, the cocaine aptasensor presented two linear responses in the concentration ranges between 0.05–1 and 1–35 μM, with an excellent detection limit of 21 nM. The proposed aptasensor provides a simple and low-cost method for cocaine detection with good reproducibility and accuracy. Furthermore, it could be regarded as a general model to investigate the unique function of aptamer-functionalized nanostructured electrodes to stablish highly advanced electrochemical biosensors for various target analytes of diagnostic importance.