An ultra-sensitive Au nanoparticles functionalized DNA biosensor for electrochemical sensing of mercury ions

The present work describes an effective strategy to fabricate a highly sensitive and selective DNA-biosensor for the determination of mercury ions (Hg²⁺). The DNA 1 was modified onto the surface of Au electrode by the interaction between sulfydryl group and Au electrode. DNA probe is complementary with DNA 1. In the presence of Hg²⁺, the electrochemical signal increases owing to that Hg²⁺-mediated thymine bases induce the conformation of DNA probe to change from line to hairpin and less DNA probes adsorb into DNA 1. Taking advantage of its reduction property, methylene blue is considered as the signal indicating molecule. For improving the sensitivity of the biosensor, Au nanoparticles (Au NPs) modified reporter DNA 3 is used to adsorb DNA 1. Electrochemical behaviors of the biosensor were evaluated by electrochemical impedance spectroscopy and cyclic voltammetry. Several important parameters which could affect the property of the biosensor were studied and optimized. Under the optimal conditions, the biosensor exhibits wide linear range, high sensitivity and low detection limit. Besides, it displays superior selectivity and excellent stability. The biosensor was also applied for water sample detection with satisfactory result. The novel strategy of fabricating biosensor provides a potential platform for fabricating a variety of metal ions biosensors.