An exonuclease-assisted amplification electrochemical aptasensor for Hg2+ detection based on hybridization chain reaction

Abstract In this work, a novel electrochemical aptasensor was developed for Hg2+ detection based on exonuclease-assisted target recycling and hybridization chain reaction (HCR) dual signal amplification strategy. The presence of Hg2+ induced the T-rich DNA partly folded into duplex-like structure via the Hg2+ mediated T–Hg2+–T base pairs, which triggered the activity of exonuclease III (Exo III). Exo III selectively digested the double-strand DNA containing multiple T–Hg2+–T base pairs from its 3'-end, the released Hg2+ participated analyte recycle. With each digestion cycle, a digestion product named as help DNA was obtained, which acted as a linkage between the capture DNA and auxiliary DNA. The presence of help DNA and two auxiliary DNA collectively facilitated successful HCR process and formed long double-stranded DNA. [Ru(NH3)6]3+ was used as redox indicator, which electrostatically bound to the double strands and produced an electrochemical signal. Exo III-assisted target recycling and HCR dual amplification significantly improved the sensitivity for Hg2+ with a detection limit of 0.12 pM (S/N=3). Furthermore, the proposed aptasensor had a promising potential for the application of Hg2+ detection in real aquatic sample analysis.