ONOO− is a strong oxidizing and nitrating agent that correlated with many pathological conditions. It forms in-vivo through fast reaction between nitric oxide and superoxide in various pathological conditions. For example, ONOO− leads to generation of reactive oxygen species (ROS) in human leukemia cells. Additionally, in acute and chronic inflammation, ONOO− generates as a highly reactive species that causes oxidation, nitration for protein, DNA bases modification, and DNA strand breaks. DNA damage frequently leads to chromosome aberrations and mitotic faults. Accumulation of mutations and/or other kinds of DNA damage represent carcinogenic or teratogenic risk. Development of analytical techniques capable of rapid and sensitive detection of various types of DNA damage and DNA damaging agents is therefore our research focus.
In our work, we detect ONOO− damaging effect using DNA films as a sensing platforms. Two methods have been used for DNA immobilization on the electrodes surfaces; grafting and layer-by-layer (LBL) methods. The former method is based on grafting glassy carbon electrode surface with carboxylic acid groups via electrochemical reduction of trans-4cinnamic acid diazonium tetrafluroborate followed by coupling of pre activated carboxylic groups with amino terminated oligonucleotide. While the LBL technique is based on depositing Poly(diallyldimethylammonium) (PDDA), a positively charged polyelectrolyte, and DNA as a negatively charged counterpart macromolecule on the surface of graphite electrode. Chronocoulometry, cyclic voltammetry, and square wave voltammetry have been used to detect the DNA damage induced by peroxynitrite through defined electrocatalytic processes. This is done through investigation of the electrochemical behavior of DNA biosensors before and after their exposure to peroxynitrite.