A new method for measuring the impedance spectra of biological cell cultures in microtiter plates (MTP) is proposed. The application offers the opportunity of measuring the complex impedance of aqueous solutions without galvanic contact. A thin polyimide film is used as dielectric layer between two metal electrodes and the solutions. The impedance of these cells or aqueous solutions is determined by measuring the impedance of the whole application and subtracting the constant capacitance of the dielectric layer. This calculation is based on a newly developed equivalent electrical circuit. To show the applicability of the sensor, yeast cells (Hansenula polymorpha wt) are monitored at frequencies between 500 kHz and 15 MHz. The results demonstrate the ability of the sensor to measure even the relaxation step of the capacitance of living cells. Because of possible side effects, the influence of aqueous solutions on the polyimide film in general is investigated as well.
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