Peptide nucleic acid as a selective recognition element for electrochemical determination of Hg

A novel electrochemical PNA-based biosensor for the determination of Hg2+ is described. The receptor layer, containing single strands of polythymine PNA (peptide nucleic acid), was formed at the surface of gold electrode. Due to the presence of thymine bases and peptide bonds, an interaction between Hg2+ ion and receptor layer occurs. The influence of chain modification - PNA vs. DNA - and type of redox marker - anionic AQMS-Na (sodium salt of anthraquinone-2-sulfonic acid) and FeII/III (potassium ferri/ferrocyanide) or cationic MB (methylene blue) and RuHex (hexaammineruthenium(III) chloride) - were studied. Proposed PNA-based biosensor with anionic AQMS-Na as a redox marker demonstrated significantly better analytical parameters, as compared to results obtained for other tested redox markers (for measurements at pH6.0). The linear response towards Hg2+ was in the range from 5 to 500nmol·L-1 with the detection limit of 4.5nmol·L-1. The developed sensor distinguishes itself with high selectivity towards Hg2+, even for solutions containing several interfering cations. Interactions between Hg2+ and PNA receptor layer were studied using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS).