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Liquid Dielectric Spectroscopy

What is liquid dielectric spectroscopy?

Dielectric spectroscopy is the process of measuring the dielectric properties of a medium as a function of frequency. This is done by placing an electric field across a dielectric medium and observing the interaction of the electric dipole moment with the field. This interaction is expressed by permittivity.


Our focus is to measure the electrostatic properties of proteins and their aggregates. We do this by taking a capacitor-like cell that can hold the dielectric medium and attaching it to an Agilent 4294A Precision Impedance Analyzer. The impedance analyzer measures the real and imaginary parts of the impedance, and with these values we are then able to extract the permittivity. Here is an overview of some of the projects we have been working on.

    Temperature Stable Cell

Since permittivity changes with varying temperature, it is essential to employ methods that ensure temperature stability within a cell. We constructed a cell that requires a large amount of a dielectric medium (800 μl) but supports a linear relationship between capacitance and permittivity.

Related Publications:

B. A. Mazzeo, S. Chandra, B. L. Mellor, and J. Arellano. Temperature-stable parallel-plate dielectric cell for broadband liquid impedance measurements. Review of Scientific Instruments 81, 125103 (2010). -also linked in Virtual Journal of Biological Physics Research, 1 January 2011

    Electrode Polarization

When a protien solution is placed into a dielectric cell, there are some ions in the solution that come very near to the surface of the electrode. As a result, the high impedance of the ions is in series with the impedance of the solution and makes noisy permittivity contributions at low frequencies. A large cell greatly redueces the amount of electrode polarization but requires a large amount of protein. Smaller cells require less protein to make measurements but incure a greater amount of electrode polarization. Our group is continually looking to reduce the effects of electrode polarization in our measurements.

Related Publications:

B. L. Mellor, N. A. Kellis, and B. A. Mazzeo. Note: Electrode polarization of Galinstan electrodes for liquid impedance spectroscopy. Review of Scientific Instruments 82, 046110 (2011). -also linked in Virtual Journal of Biological Physics Research, 1 May 2011.

B. L. Mellor, E Cruz Cortes, S. Khadka, and B. A. Mazzeo. Increased bandwidth for dielectric spectroscopy of proteins through electrode surface preparation. Review of Scientific Instruments 83, 015110 (2012).

    Smaller Cells

While larger cells have yielded promising results with relatively few obstacles, a large amount of protein is required in order to run experiments. Smaller cells are more economical and could prove to be advantageous in other aspects of dielectric spectroscopy as more research is performed. Our group has experimented with primarily two types of smaller cells, one of which is described below in the Related Publications section, and another which has a U-shaped, 200 μl cavity to hold protein solution while carrying out an experiment.

Related Publications:

B. L. Mellor, N. A. Kellis, and B. A. Mazzeo. Dielectric Spectroscopy of Molecular Interactions Based on the Avidin-Biotin Complex. 33rd Annual International IEEE EMBS Conference. Boston, MA. 30 August-3 September 2011.