SUNY at Albany
June 19-23, 2001
MercuryY Electrodes as Sensitive Tools in the Studies of DNA Structure, Interactions and Damage
Nucleic acids are electroactive and surface-active substances producing a number analytically useful signals at mercury and solid electrodes (1). Recent trends in the development of electroanalytical techniques and electrochemical sensors that utilize DNA as a recognition layer are predominantly based on applications of solid electrodes. However, DNA signals that can be obtained only with the mercury electrodes at very negative potentials (2-1.3 V) exhibit a unique sensitivity to subtle alterations in DNA conformation; such a sensitivity cannot be achieved using the solid electrodes. Mercury electrodes modified with DNA can be used as sensors for DNA damage, DNA structural transitions, monitoring of DNA interactions with other species, etc. Formation of DNA strand breaks can be sensitively detected by measuring DNA AC voltammetric peak 3 which is yielded by single stranded DNA and, under certain conditions, by double-stranded DNA containing free ends, but not by covalently closed circular (supercoiled, sc) DNA (2) . DNA strand breaks can be generated at the mercury electrode surface. In this case, the scDNA-modified electrode serves as a sensor for DNA cleaving agents. Cleavage of electrode surface-confined DNA with enzymes (DNase I) (3) as well as by chemical nucleases (e.g., hydroxyl radicals generated in Fenton reactions) (4) can be modulated by the electrode potential. Based on the measurements of DNA adsorption/desorption behavior at the mercury electrodes, it is possible to detect structural transitions in negatively supercoiled DNA (5) , formation of DNA complexes with intercalators (6) , to differentiate between DNA , RNA and peptide nucleic acid (7) , etc. Besides intrinsic DNA peaks, signals of substances that interact with DNA covalently (e.g., osmium tetroxide complexes) or non-covalently (e.g., intercalators such as doxorubicin or echinomycin) can be utilized to follow DNA interactions. To create a simple biosensors applicable not only in a specialized laboratory but also in a doctor's office or in the field, the classical hanging mercury drop electrode can be replaced by other electrode types working with the mercury surface, e.g. mercury film electrodes (8) or mercury meniscus electrodes on silver amalgam surfaces (9,10).
This work was supported by grants of the Grant Agency of the Czech Republic No. 204/97/K084 and of the Grant Agency of the Academy of Sciences of the Czech Republic No. A4004108.References and Footnotes
Miroslav Fojta, Ludek Havran, Frantisek Jelen, Rene Kizek and Emil Palecek
Institute of Biophysics, Academy of Sciences of the Czech Republic, 612 65 Brno