An ultra-sensitive and highly selective electrochemical label-free aptasensor is proposed for the quantitation of Hg2+ based on the hybridization/dehybridization of doublestranded DNA (dsDNA) on a gold electrode. Thiol-substituted single-stranded DNA (ssDNA) is self-assembled on the gold electrode surface through the S–Au interaction. The hybridization of ssDNA with complementary DNA (cDNA) and the consequences of dehybridization in the presence of mercury ions are followed through differential pulse voltammetry (DPV) responses using a [Fe(CN)6]3-/4- redox probe. The formation of a thymine–Hg2+–thymine (T–Hg2+–T) complex is the key to producing a highly selective and sensitive aptasensor for Hg2+ determination. Specifically, the present electrochemical aptasensor is able to quantify Hg2+ ions in concentrations from 5 zeptomolar (zM) to 55 picomolar (pM) with a limit of detection of 0.6 zM, close to the dream of single atom detection, without requiring a complicated procedure or expensive materials.
