Using Electrochemical Impedance Spectroscopy of Methylene Blue and Ferricyanide for DNA Sensing Surface Characterization
In pathogen diagnosis, a single stranded target DNA may be detected in a sensor carrying an active surface with a recognition layer of its complementary single stranded DNA (ssDNA probe). Such a surface may be the core of a specific DNA sensing electrode. The density of probe ssDNA should then be optimized to display the greatest sensitivity to the target DNA. In this work we utilize the electrochemical impedance spectroscopy (EIS) on the electrode reactions for ferri/ferrocyanide ([Fe(CN)6]3−/4−) and methylene blue (MB) to characterize different stages along the development of an indium tin oxide (ITO)-DNA sensor for target ssDNA after PCR amplification. In particular, we study the effects of applied DC potential pretreatments on the ferri/ferrocyanide-electrode interaction. The effect of the electrostatic repulsion by negative charges of single stranded DNA (ssDNA) was observed to affect the rate of the overall reaction rates for the redox couples. On one hand, EIS spectra for the [Fe(CN)6]3−/4− reaction on DNA modified ITO surfaces yielded time-independent fitting parameters which were consistent with the scanning electrochemical microscopy (SECM) images. On the other hand, MB species yielded time-dependent parameters due to adsorption and intercalation processes that take place on DNA. Models were proposed to explain such time-dependent behavior. The results of the impedance measurements were explained in terms of the variation of the surface charge for different densities of probe ssDNA.
KeywordsMethylene Blue Electrochemical Impedance Spectroscopy Open Circuit Potential Constant Phase Element Probe Concentration
Suthisa Leasen gratefully thanks for the financial support from Commission on Higher Education. The authors also thank Genome Institute of National Center for Genetic Engineering and Biotechnology for characterizing synthesized oligonucleotides.
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