Electrode design improvement for impedance evaluation of biological cell culture under variable frequency low intensity sinusoidal electric field

In this paper the electrode geometry effects on the impedance spectroscopy of biological cell culture have been studied under low intensity sinusoidal electric field with a view to design improved electrode structures for continuous cell growth monitoring. To achieve this, impedance estimation has been done by modified distributed analysis both in presence and absence of confluent cell layer by taking into account the effect of solution resistance and the separation between the electrodes. The model has been applied on fibroblast cell culture (3T3) in the frequency range of 10 Hz to 10 kHz. It has been observed that for most of the frequencies, the resistance sensitivity (S_r) is less than the capacitance sensitivity (S_c) and does not increase monotonically with radius of working electrode (R_e) unlike S_c. Further, the nature of variation of S_r and S_c are fairly contradictory with variation in Re and separation between the electrodes (d-Re). Thus an optimum geometry has been selected based on a figure of merit (FOM) which has been defined as the product of S_r and S_c. The maximum FOM corresponds to R_e=90 μm and d=3R_e for a typical frequency of 4 kHz. Observations at 4 kHz show that the optimized geometry yields values of Sr that are almost 5 times higher than those from the conventional geometry (R_e=125 μm and d=300R_e). This increase permits the small signals resulting from the micromotion of cells to be more easily seen.