Of the available on-line biomass assays, the radio-frequency impedance method (often referred to as capacitance) is generally regarded as the most robust and reliable method to monitor viable biomass during fermentation and cell culture.
The first paper to show that capacitance could be used to estimate microbial biomass dates back over 20 years, and today the technology is routinely used for monitoring and controlling mammalian cell culture processes and high-density yeast and bacterial fermentations in research, process development, and manufacturing applications.
The capacitance method has been shown to be robust, easy to scale up, and insensitive to gas bubbles or debris with cells in suspension or attached to inert carriers.
In this article, we show how capacitance measurements for live-cell concentration can be more widely applied to disposable bioreactors as a result of the availability of a dedicated disposable biomass probe. These days an increasing number of disposable bioreactors can be used with conventional reusable biomass probes. We also show how major improvements have been made to installation/operation qualification procedures so that conventional reusable probes can also be utilized within a cGMP production environment.