New light-scattering and field-trapping methods access the internal electric structure of submicron particles, like influenza viruses.

A variety of AC-electrokinetic field effects can be exploited for handling or electric characterization of microscopic and submicroscopic particles, like cells, organelles, supramolecular structures, and artificial colloids. Despite the fact that dielectric spectroscopy methods by AC-electrokinetics, like common impedance methods, are based on the impedance properties of the different constituents of the particles, the first methods yield higher parameter resolutions. A drawback of the electrokinetic methods was that they required microscopic observability of field-induced particle movements. New AC-electrokinetic methods like electrorotational light scattering (ERLS), dielectrophoretic phase-analysis light scattering (DPALS), and dielectrophoretic field trapping (DFT) solve this problem and access the submicroscopic particle range. This paper gives an introduction to the new methods and presents measurements on influenza viruses. To develop a dielectric virus model, experiments of ERLS were combined with DFT of viruses in microstructured electric-field cages. The model assumes a spherical virus with a radius of 50 nm and a single-shell dielectric structure. The shell thickness of 18 nm summarizes the dimensions of the lipid and viral surface protein layers. For this model, the conductivities of core and shell of 0.1 mS/m and 0.1 microS/m, respectively, and the relative permittivities of 30 and 80, respectively, were obtained.