Electrochemical Sensor Based on Electrodeposited Graphene-Au Modified Electrode and NanoAu Carrier Amplified Signal Strategy for Attomolar Mercury Detection

An electrochemical sensor was developed for attomolar Hg2+ detection. Three single-stranded DNA probes were rationally designed for selective and sensitive detection of the target, which combined T-Hg2+-T coordination chemistry and the characteristic of convenient modification of electrochemical signal indicator. Graphene and nanoAu were successively electrodeposited on a glass carbon electrode surface to improve the electrode conductivity and functionalize with the 10-mer thymine-rich DNA probe (P1). NanoAu carriers functionalized with 29-mer guanine-rich DNA probe (P3) labeled methyl blue (MB-nanoAu-P 3s) were used to further strengthen signal response. In the presence of Hg2+, a T-T mismatched dsDNA would occur between P1 and a 22-mer thymine-rich DNA probe (P2) on the electrode surface due to T-Hg2+-T coordination chemistry. Followed by adding the MB-nanoAu-P 3s for hybridization with P2, square wave voltammetry was executed. Under optimal conditions, Hg2+ could be detected in the range from 1.0 aM to 100 nM with a detection limit of 0.001 aM. Selectivity measurements reveal that the sensor is specific for Hg2+ even with interference by high concentrations of other metal ions. Three different environmental samples were analyzed by the sensor and the results were compared with that from an atomic fluorescence spectrometry. The developed sensor was demonstrated to achieve excellent detectability. It may be applied to development of ultrasensitive detection strategies.