A structure-switching electrochemical aptamer sensor for mercury ions based on an ordered assembled gold nanorods-modified electrode

In this paper, an electrochemical aptamer sensor with high sensitivity and selectivity was proposed for the detection of mercury ion (Hg2+). The orderly assembled gold nanorods-modified screen-printed electrode (AuNRs/SPE) was used to improve the sensor with higher sensitivity and data reproducibility. The sensor was designed based on the specific recognition of Hg2+ with aptamer to form T-Hg2+-T binding structure. Two aptamer chains were applied in the designed sensor, aptamer S1 with terminal thiolate group was self-assembled on the AuNRs/SPE via Au-S bond, and complementary S2 labeled with ferrocene (Fc) would generate a strong redox electrical signal. The addition of Hg2+ would mediate the folding of the T-base of S1 to form a hairpin structure, resulting in the dissociation of the Fc-labelled S2 from the sensing system and a significant reduction in the redox current. The electrochemical properties of the sensor were further investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The effects of aptamer reaction time, concentration, and target incubation time on the sensor response were also investigated. The results showed that the sensor had a sensitive response to Hg2+ at concentrations ranging from 1 pM to 1 μM, with a detection limit of 0.3 pM. Furthermore, the proposed sensor was applied in the determination of Hg2+ in real samples, demonstrating its potential practical value.