Graphite composite electrodes for the determination of glucose, electroactive analytes and DNA

Enzyme electrodes were constructed by immobilization of glucose oxidase and ferrocene into cross-linked polyacrylamide gels. Electrogenerated ferrocinium ion acts as a direct electron mediator between glucose oxidase and a reticulated vitreous carbon (RVC)/graphite support bed. The electrode is easily constructed, gives a current response proportional to glucose concentrations up to 30 mM, and has good chemical stability in water and air.

To demonstrate that polyacrylamide gel electrodes can be used as permeable, multicomponent interfaces between an electrode substrate and solution, charge transport through the ferrocene/graphite/gel composite was studied. In addition, solutions of electroactive analytes (ferricyanide, benzoquinone and methyl viologen) were sorbed into dehydrated graphite/polyacrylamide gel electrodes to investigate the possible use of these electrodes as working electrodes for electroanalysis. Another approach was to replace the graph ite in the gel composite with titanium dioxide. It was found that the TiO₂ particles acted as light-activated charge transport centers for ferrocene mixed into the gel composite.

Ethidium tetracyanoquinodimethane/carbon paste composite electrodes were fabricated and studied in contact with aqueous solutions. Low coulombic efficiencies for the potential dependent release of ethidium cation from the electrode surface were observed due to insoluble ethidium salt formation on or in the electrode. In the presence of calf thymus « DNA solutions, potential-dependent binding of DNA to the electrode surface was observed which allowed for the transfer of absorbed DNA to remote solutions. Release and intercalation of ethidium cation into the double helical structure of DNA, near the electrode surface, was also studied by monitor ing the fluorescence of the intercalated ion. Fluorescence intensity was proportional to DNA concentration in solution.