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

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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 (fC) was calculated from the on-line scanning permittivity measurements. The fC 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 fC were qualitatively explained by the underlying equation that is correlating fC and the properties of the cell population (cell diameter, intracellular conductivity and capacitance per membrane area).

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Cole–Cole alpha

CM :

Capacitance per membrane area (F m−2)


Cell permittivity (pF cm−1)


Permittivity difference at f1 and f2 (pF cm−1)

fC :

Characteristic frequency (Hz)




Volumetric oxygen mass transfer coefficient (h−1)


Phosphate buffered saline


Packed cell volume (μL mL−1)


Time of infection with baculovirus (h)


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The authors would like to acknowledge C. Ghommidh from Université Montpellier II and M. Biselli from the Aachen University of Applied Sciences (Department Juelich) for the stimulating and fruitful discussions and remarks, M. Foggetta, M. Siegrist, J.-M. Vonach and J.-C. von Bueren for the support with small scale experiments and the setup of the bioreactor system and H. Remy for the use and help with the CASY®1 system. S. Ansorge was supported from March to September 2004 by a Hoffmann-La Roche AG fellowship and the presented results form a part of his diploma thesis at the Aachen University of Applied Sciences.

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Correspondence to Sven Ansorge.

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Ansorge, S., Esteban, G. & Schmid, G. On-line monitoring of infected Sf-9 insect cell cultures by scanning permittivity measurements and comparison with off-line biovolume measurements. Cytotechnology 55, 115–124 (2007).

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