One study used capacitance via dielectric spectroscopy to monitor viable xanthamonous bacterial cells within a 2000L seed fermentor. Kelco UK was a company using 2000L fermenters in order to create Xanthamonous bacterial seeds to be transferred to a production vessel. Aber Futura systems were initially used in order to first better understand the growth of the seeds, then it was later used to help better understand when to extract the seeds.
CHO cells are the most common mammalian cell line used for mass production of therapeutic proteins. Aber Radio Frequency Impedance (RFI) probes are commonly used to both monitor and control these processes.
A study was carried out by Millipore (US) to assess the performance of both the multi-use annular probe and the disc style probe with flush platinum electrodes in a 3 L rigid plastic bioreactor (Carvell et al., 2011). The disposable probe was connected to a light weight “Mini‐Remote Futura” pre‐amplifier and the bio capacitance was converted into cells/ml by using a simple linear correlation factor. The calculated cell concentrations were compared with off‐line measurements from the Vi‐cell (Beckman Coulter, USA).
The capacitance measurements from both probes show a similar growth trend which correlate with the off‐line measurements up to the peak cell concentration on day 6. In the death phase there was a small divergence between the on‐line and off‐line data. This divergence has been studied in more detail by a number of groups (Braasch et al., 2013, Lee et al., 2015) and it is indicated that the differences during the death phase can relate to changes in bio‐volume or it can be attributed to the bio capacitance method picking up changes at the cellular level due to apoptosis at a much earlier phase than the trypan blue method. When investigating the online capacitance and offline measurements closely, there could be a strong argument that the RFI measurement provides a signal that is more closely related to the metabolic activity of the cells (Braasch et al , 2013).