On-line monitoring of infected Sf-9 insect cell cultures by scanning permittivity measurements and comparison with off-line biovolume measurements

Abstract

Two infected Sf-9 cell cultures were monitored on-line by multi-frequency permittivity measurements using the Fogale BIOMASS SYSTEM^® and by applying different off-line methods (CASY^®1, Vi-CELL™, packed cell volume) to measure the biovolume and the mean diameter of the cell population. During the growth phase and the early infection phase the measured permittivity at the working frequency correlated well with the different off-line methods for the biovolume. We found a value of 0.67 pF cm⁻¹ permittivity per unit of total biovolume (CASY) (μL mL⁻¹). After the maximum value in the permittivity was reached, i.e. when the viability of the cultures decreased significantly, we observed different time courses for the biovolume depending on the applied method. The differences were compared and could be explained by the underlying measurement principles. Furthermore, the characteristic frequency (f_C) was calculated from the on-line scanning permittivity measurements. The f_C may provide an indication of changes in cell diameter and membrane properties especially after infection and could also be an indicator for the onset of the virus production phase. The changes in f_C were qualitatively explained by the underlying equation that is correlating f_C and the properties of the cell population (cell diameter, intracellular conductivity and capacitance per membrane area).