The quality by design (QbD) and process analytical technology (PAT) approaches have shown significant benefit in the classical pharmaceutical industry and are now strongly influencing bioprocessing. Monitoring critical process parameters (CPPs) during biotechnological cell cultivations is essential to maintaining high efficiencies and quality. Commercial sensor systems for real-time inline monitoring are available for some parameters, such as pH or the concentration of dissolved oxygen (DO). For others such as glucose concentration, total cell count (TCC), and viability no robust online…