A regenerative electrochemical biosensor for mercury(II) by using the insertion approach and dual-hairpin-based amplification

Highlights: • The dual-hairpin structure as a signal amplifier is label-free and handy. • The strategy uses the insertion approach to improve the hybridization efficiency. • This biosensor has a low detection limit (28 pM) for detection of Hg²⁺. • This biosensor can be easily regenerated by using L-cysteine. - Abstract: A simple and effective biosensor for Hg²⁺ determination was investigated. The novel biosensor was prepared by the insertion approach that the moiety-labeled DNA inserted into a loosely packed cyclic-dithiothreitol (DTT) monolayer, improving the hybridization efficiency. Electrochemical impedance spectroscopy studies of two biosensors (single-hairpin and dual-hairpin structure DNA modified electrodes) used for Hg²⁺ detection indicated that the dual-hairpin modified electrode had a larger electron transfer resistance change (ΔR_ct). Consequently, the dual-hairpin structure was used as a signal amplifier for the preparation of a selective Hg²⁺ biosensor. This biosensor exhibited an excellent selectivity toward Hg²⁺ over Cd²⁺, Pd²⁺, Co²⁺ etc. Also, a linear relation was observed between the ΔR_ct and Hg²⁺ concentrations in a range from 0.1 nM to 5 μM with a detection limit of 28 pM under optimum conditions. Moreover, the biosensor can be reused by using L-cysteine and successfully applied for detecting Hg²⁺ in real samples