ELECTROROTATION OF PARTICLES MEASURED BY DYNAMIC LIGHT-SCATTERING - A NEW DIELECTRIC-SPECTROSCOPY TECHNIQUE

Electrorotation provides information about the dielectric and conductive properties of particles over a large frequency range, which is not easily available from other techniques. Numerous applications of the dielectric particle spectroscopy technique have already been demonstrated by microscopic measurements in the held of biology. Aware of the serious limitations of microscopy for applications in colloid science, we demonstrate that dynamic light scattering can be used to measure electrorotation spectra. A suitable chamber was designed which fits into a commercial correlation spectrometer. Measurements on human red blood cells showed that the apparent diameter of the particles recorded as a function of the frequency of the rotating field matches the microscopically measured electrorotation spectrum. However, the applicability of conventional dynamic light scattering sizing-devices to the recording of electrorotation spectra is limited, since the autocorrelation function in the presence of particle rotation is a superposition of zero-order Bessel functions. Consequently, new mathematical techniques have to be developed. Another limitation is that the direction of rotation is not yet detectable. Nevertheless, since the new method overcomes the restrictions of microscopic observations it offers a potentially wide range of applications for colloidal particles, vesicles, microemulsions, subcellular particles, and cells.