We report on impedance measurements of fluids to examine the impact of the length and concentration of free-floating double-stranded DNA molecules. The impedance versus frequency characteristics were fitted to an equivalent circuit model including solution dielectric capacitance and conductance. The extraction of these parameters can be used to detect the presence of DNA molecules in the nanomolar range for a 400 bp long molecule. Our results show that the extracted dielectric capacitance and conductance increase with molecule length and concentration owing to a corresponding increase in number of molecule dipoles and counterions in solution. © 2008 American Institute of Physics.
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