An electrochemical aptamer biosensor based on “gate-controlled” effect using β-cyclodextrin for ultra-sensitive detection of trace mercury

A new strategy for construction an electrochemical biosensor for Hg2+ analysis with extremely high sensitivity was proposed based on “T-Hg2+-T” coordination by aptamers and “gate-controlled” amplification by switch of the channels of the probe. SH-β-cyclodextrin was self-assembled on the gold electrode to form an orderly arranged molecularly layer with interspaces among β-CDs; thionine labeled aptamer was then linked on the assembled β-CD. When Hg2+ was added, the aptamer combined with Hg2+ and formed “T-Hg2+-T” structure, which caused the aptamer folded and the labeled thionine covered the interspaces to block off the channel for probe entrance. The oxidative current of probe decreased, which provide the basis for the determination of Hg2+. With the gate-controlled amplification, the changes of trace amounts of Hg2+ will produce great changes of the probe current. The sensor exhibited significantly higher sensitivity with a detection limit of 5.0×10−15 mol/L, which is lower than other reported methods.