A novel electrochemical method to detect mercury (II) ions

A novel and sensitive electrochemical method for determination of mercury (II) ions (Hg2+) based on the formation of thymine-Hg2+-thymine complexes and gold nanoparticle-mediated signal amplification is reported. Two 5' end thiolated complementary oligonucleotides containing six strategically placed thymine-thymine mistakes were introduced in this work. One of the two oligonucleotides was immobilized on a gold electrode and the other one on gold nanoparticles (AuNPs). Due to six thymine-thymine mistakes the two oligonucleotides were not able to be hybridized, so AuNPs could not be immobilized onto the electrode surface after the electrode was immersed in the DNA-AuNPs solution. However, if Hg2+ existed, T-Hg2+-T complexes could be formed and AuNPs could be immobilized onto the electrode surface. Meanwhile, large numbers of [Ru(NH3)(6)](3+) molecules as electrochemical species could be localized onto the electrode surface. The Hg2+ detection limit of this assay could be as low as 10 nM, which is the US Environmental Protection Agency (EPA) limit of Hg2+ for drinkable water. This method is proven to be simple, convenient, high sensitive and selective. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.