Dielectric relaxation of DNA aqueous solutions

Abstract

We report on a detailed characterization of complex dielectric response of Na-DNA aqueous solutions by means of low-frequency dielectric spectroscopy (40 Hz-110 MHz). Results reveal two broad relaxation modes of strength 20<Deltaepsilon(LF)<100 and 5<Deltaepsilon(HF)<20, centered at 0.5 kHz<nu(LF)<70 kHz and 0.1 MHz<nu(HF)<15 MHz. The characteristic length scale of the low-frequency (LF) process, 50<L(LF)<750 nm, scales with DNA concentration as c(DNA)(-0.29+/-0.04) and is independent of the ionic strength in the low added salt regime. Conversely, the measured length scale of the LF process does not vary with DNA concentration but depends on the ionic strength of the added salt as I(s)(-1) in the high added salt regime. On the other hand, the characteristic length scale of the high-frequency (HF) process, 3<L(HF)<50 nm, varies with DNA concentration as c(DNA)(-0.5) for intermediate and large DNA concentrations. At low DNA concentrations and in the low added salt limit the characteristic length scale of the HF process scales as c(DNA)(-0.33). We put these results in perspective regarding the integrity of the double stranded form of DNA at low salt conditions as well as regarding the role of different types of counterions in different regimes of dielectric dispersion. We argue that the free DNA counterions are primarily active in the HF relaxation, while the condensed counterions play a role only in the LF relaxation. We also suggest theoretical interpretations for all these length scales in the whole regime of DNA and salt concentrations and discuss their ramifications and limitations.

Label-free electronic probing of nucleic acids and proteins at the nanoscale using the nanoneedle biosensor

“…It is thus impossible to completely separate condensed counterions from free counterions in their contribution to the LF relaxation mode. Dielectric data from previous work 35 indicate that at low frequencies the decoupling of MO condensed and free DNA counterions are both responsible for the response, in addition to the counterions along a single DNA chain.…”

“…When an AC field is applied, polarization is induced and a flow of net charge resulting from the DNA counterions 35 occurs. Diffusion controls the movement of counterions, thus the dielectric response is dictated by the mean relaxation time,…”

Direct measurement of the dielectric polarization properties of DNA

“…In particular, standard dielectric characterization tools such as impedance spectroscopy (18,19) and dielectrophoresis (20,21) only yield average values of DNA polarizability in bulk solution that include major structural contributions and DNA-solvent interfacial effects. Microscopic measurements with dielectric sensitive fluorescence dyes (22,23) reflect the DNA microenvironment rather than the DNA polarizability.…”

Ionic mobility in DNA films studied by dielectric spectroscopy

“…Studies of the dielectric dispersion of DNA have a long history as they started even before its molecular structure had been discovered [1] and were regularly pursued since then [2][3][4][5][6][7][8][9]. There is a double motivation for these studies.…”

“…Then speculations on the mechanism of electronic conduction along DNA were at the origin of various attemps to measure its electrical conductivity, including studies of wet-spun solid samples [12]. This long history does not mean that all questions are solved, as discussed for instance in a more recent paper [9].…”