Analytical Sciences

Label-free Electrochemical Cocaine Aptasensor Based on a Target-inducing Aptamer Switching Conformation

Mei HUA,* Manlan TAO,* Ping WANG,* Yinfeng ZHANG,* Zaisheng WU,** Yanbing CHANG,* and Yunhui YANG*

*College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650092, P. R. China
**State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha 410082, P. R. China

A novel label-free electrochemical nucleic acid aptasensor for the determination of cocaine by the immobilization of thiolated self-assembled DNA sequences on a gold nanoparticles-modified electrode is presented. When cocaine was complexed specifically to the aptamer, the configuration of the nucleic acid aptamer switched to a locked structure and the interface of the biosensor changed, resulting in a variation of the corresponding peak current of an electrochemical probe ([Fe(CN)₆]^3−/4−). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize modifications of the electrode surface. The peak current was detected by differential pulse voltammetry (DPV). Under the optimized experimental conditions, the presented sensor exhibits a nice specificity towards cocaine. The decrease of the peak current response of the aptasensor has a linear relationship with the concentration of cocaine ranging from 1.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit of 3 × 10⁻⁷ mol L⁻¹ at 3σ. The proposed aptasensor can be easily regenerated by the denaturalization of aptamer-target complexes in a heated water bath at 80 – 90°C. Besides, this biosensor has a high reproducibility and selectivity, which can be a promising method to detect cocaine in real samples.

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