Ultramicrostructures
Ultramicroelectrode Chambers
Dielectric spectroscopy at physiological ionic strength
Usually dielectrophoretic and electrorotation measurements are carried out at low ionic strength to reduce electrolysis and heat production. Such problems are minimized in ultramicroelectrode chambers. In a planar ultramicroelectrode chamber fabricated by semiconductor technology, we were able to measure the dielectric properties of biological cells in the frequency range from 2 kHz to 200 MHz up to physiological ion concentrations (conductivity range: 1 mS/m to 1.5 S/m). Since the polarizability of the external medium and the cytoplasm can now be balanced, special features of the spectra can be measured more sensitively [39].
Resonance phenomena
Micro-structures with unterminated electrodes exhibit resonance phenomena depending on electrode size and arrangement. In our chambers, resonances drastically change the observed electrorotational spectra above 30 MHz and must be considered when calculating dielectric cell and particle data. Possibly, chamber resonances can be technologically applied: With constant driving voltages at the chamber connectors, resonances may cause a local, extraordinary increase in the chamber field strength and the resulting ponderomotive forces. This effect seems useful for the construction of ultramicrochambers for cell and particle separation, manipulation and field caging [Fuhr, et al., Cell. Eng. 1: 47-57 (1995)]. Another application is the construction of micro-motors and actuators [41]. For these applications, increasing the inductance of the feed wires or the addition of capacitive elements will shift the resonance increase of induced forces to lower frequencies.
More information: Jan Gimsa