On-line biomass monitoring of CHO perfusion culture with scanning dielectric spectroscopy.

In this work, dielectric spectroscopy was used to monitor two CHO perfusion culture experiments (B14 and B16). The capacitance of the cell suspension was recorded every 20 minutes over an excitation frequency range of 0.2 MHz to 10.0 MHz. A phase plot of the capacitance at a low excitation frequency vs. the value at a higher frequency proved to be an accurate indicator of the major transition points of the culture, i.e., maximum cell viability, end of lactate consumption, point of zero viability. For both experiments, the capacitance signal correlated very well (R(2) >0.98) with viable cell number up to concentrations of 1 x 10(7) cells/mL. Visual observation of the capacitance spectra indicated that changes in the capacitance relative to frequency were related to the cellular morphology. A multivariate model was developed using off-line data that could predict the median cell diameter within a single experiment (B14) with an error of 0.34 microm (2%). Upon extension to a subsequent experiment (B16), the predicted error was 1.18 microm (9%).