LOW-FREQUENCY DISPERSION OF SURFACE CONDUCTING PARTICLES AS MEASURED BY MEANS OF ELECTROROTATION

Electrorotation of glutaraldehyde-fixed red blood cells (RBCs) has bee n investigated in the frequency range from 16 Hz to 30 MHz. Special em phasis has been given to the low-frequency range (16 Hz-2 kHz). In thi s region, a distinctly new type of co-field rotation peak was observed . Native RBCs also show low-frequency rotation, but much less pronounc ed. The low-frequency rotation is nonmonotonous with regard to conduct ivity. With increasing external conductivity, the low-frequency rotati on speed reaches a maximum of around 3.5 mS/m and decreases again when the external conductivity is increased further. The low-frequency co- field rotation peak was observed between 30 Hz and 70 Hz except at ver y low conductivity almost independent of electrolyte concentration. De creasing surface charge density by means of neuraminidase led to a red uction of the rotation speed in the low-frequency range. The position of the peak remained unaffected by changes of the surface charge densi ty. These experimental results are not consistent with the typical Pau li-Schwan- and Maxwell-Wagner-dispersion. They rather suggest the pres ence of a concentration polarization mechanism responsible for the low -frequency electrorotation peak. (C) 1998 Elsevier Science B.V. All ri ghts reserved.