The Scaling of Electrochemical Parameters of DNA Aqueous Solutions with Concentration and Temperature Through an Electrochemical Impedance Spectroscopy Study

In this work, Electrochemical Impedance Spectroscopy (EIS) is used to characterize transitional behavior of calf thymus DNA molecules as a function of DNA concentration (0.01 up to 2.5 mg mL−1) and temperature (10, 20, 30 and 40 °C) at a pH of 7.3. Here it is proposed a novel method able to analyze the temperature and concentration effects on polymeric molecules such as DNA in their different characteristic regimes, in which are present diverse chain interactions, through the electrochemical parameters provided by the EIS technique. The results obtained are interpreted in terms of an EIS classical analysis and a methodology similar to the one used in studies by oscillatory linear-rheology measurements, i.e. log–log Bode plots (real (Z′) and imaginary (-Z″) impedance components vs. ω), from which is possible to easily determine both impedance characteristic crossover frequency (ωc), and Zo, related to the solution resistance (Rs). It is possible to detect the overlap and the entanglement concentrations of the system, C* and Ce, respectively, from the analysis of Zo and the characteristic time-constant of the process τc (1/ωc) as a function of DNA concentration. The parameters Zo and τc exhibit three regimes according to a power law dependence with DNA concentration for all the studied temperatures. Once the scaling of the electrochemical parameters, Zo and τc, was established, it was possible to generalize an impedance transfer function for DNA adsorption process on platinum electrodes as a function of CDNA. This transfer function allows to predict the impedance behaviour at OCV for a chosen DNA concentration within a specific regime and to analyze theoretically the double-layer charging of the interface as a function of DNA concentration with only one impedance experiment.