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The ionic strength dependence of DNA mediated charge transport was studied on a DNA binding polyamide-modified electrode by the electrochemical method. The differential pulse voltammetry peak potential of [Ru(NH3)6]3+shifted negatively as the support electrolyte concentration increased. A linear relationship was observed between the peak potential and ionic strength in the solution at moderate salt concentrations. This could be interpreted with Debye-Hückel theory using formal potential as a“bridge”, which linked experiments results and theoretical y calculated values. At high salt concentrations, this linear relationship deviated from Debye-Hückel theory prediction because it was outside the range of validity. Without added salt in the solution, the ful y charged DNA duplex wil strongly attract the probe molecule [Ru(NH3)6]3+to the broadened p-stack of a DNA-polyamide complex, which facilitates DNA mediated charge transport.