APPLICATION OF PHOTOCHEMICAL-REACTION IN ELECTROCHEMICAL DETECTION OFDNA INTERCALATION

A flow injection analysis (FIA) system for the detection of the compou nds that intercalate within DNA is reported. A derivative of 9,10-anth raquinone has been used as the reference compound for photoelectrochem ical detection. The sodium salts of 9,10-anthraquinone-2,6-disulfonic acid and 9,10-anthraquinone-2-sulfonic acid are photochemically activa ted and then reduced in the presence of an electron donor (glucose). T he electrochemical signal is based on the measurement of the anodic cu rrent resulting from the oxidation of the reduced form of 9,10-anthraq uinone. The reduced form of the 9,10-anthraquinone is oxidized through a mediated mechanism at the surface of a tetracyanoquinodimethane-(TC NQ)-modified graphite paste electrode covered by a Nucleopore membrane . TCNQ acts as an efficient mediator for the oxidation of reduced 9,10 -anthraquinone. Cyclic voltammetry, photocyclic voltammetry, and the p hotoelectrochemical FIA response of 9,10-anthraquinone are reported, E xperimental results show that these anthraquinones can be intercalated within the helix of double-stranded calf thymus DNA. The anthraquinon e molecules that are intercalated within DNA cannot be oxidized due to their limited transport to the modified electrode surface. This resul ts in a decrease in the anodic current at a constant concentration of anthraquinone after intercalation. There is a linear relation between the decrease in electrochemical response and the DNA concentration at a constant concentration of anthraquinone. The intercalated anthraquin one molecules can be completely replaced by another intercalating agen t (i.e., ethidium bromide) that is more strongly intercalated within D NA, thereby regenerating the electrochemical response. The calibration curve for the analysis of this compound is reported.