Novel probes for pH and dissolved oxygen measurements in cultivations from millilitre to benchtop scale

Abstract

pH value and the concentration of dissolved oxygen (DO) are key parameters to monitor and control cell growth in cultivation studies. Reliable, robust and accurate methods to measure these parameters in cultivation systems in real time guarantee high product yield and quality. This mini-review summarises the current state of the art of pH and DO sensors that are applied to bioprocesses from millilitre to benchtop scale by means of a short introduction on measuring principles and selected applications. Special emphasis is placed on single-use bioreactors, which have been increasingly employed in bioprocess development and production in recent years. Working principles, applications and the particular requirements of sensors in these cultivation systems are given. In such processes, optical sensors for pH and DO are often preferred to electrochemical probes, as they allow semi-invasive measurements and can be miniaturised to micrometre scale or lower. In addition, selected measuring principles of novel sensing technologies for pH and DO are discussed. These include solid-state sensors and miniaturised devices that are not yet commercially available, but show promising characteristics for possible use in bioprocesses in the near future.

Numerical and experimental assessment of a miniature bioreactor equipped with a mechanical agitator and non‐invasive biosensors

“…Another challenge for miniature bioreactors is process control, particularly for pH and DO in minimal space. Many studies have developed optical sensors for the determination of pH and DO, which have greatly promoted the development of miniature bioreactors …”

Integration and application of optical chemical sensors in microbioreactors

“…a Department of Biochemical Engineering, University College London, Gower optical sensors have gained popularity due to their typically low cost, compact size, and capability to monitor analytes in a non-invasive fashion. Optical sensors for oxygen are widely applied nowadays and feature in environmental monitoring, bioprocess monitoring, 3 and in life sciences. 3,4 Optical sensors also played a crucial role in establishing new fields: online and in situ detection of process variables from microliter volumes was at the heart of the successful development of miniaturized and microIJfluidic) bioreactors.…”

“…Optical sensors for oxygen are widely applied nowadays and feature in environmental monitoring, bioprocess monitoring, 3 and in life sciences. 3,4 Optical sensors also played a crucial role in establishing new fields: online and in situ detection of process variables from microliter volumes was at the heart of the successful development of miniaturized and microIJfluidic) bioreactors. 5,6 In the wake of the success of optical sensors for oxygen, sensors for other analytes relevant for bioprocess monitoring were researched and developed.…”

Raman spectroscopy as a method to replace off‐line pH during mammalian cell culture processes

“…Controlling pH, an important process parameter is dependent on the cellular expression system being utilized (Demuth, Varonier, Jossen, Eibl, & Eibl, 2016). Typically, a two-sided controller (carbon dioxide or hydrochloric acid and sodium carbonate) and a pH deadband are used to maintain the pH for mammalian cell culture.…”

“…The measurement of pH to enable control is commonly executed by a probe inserted in the bioreactor. Technology for measuring pH in bioprocesses has traditionally been performed by electrochemical probes and newer methods utilize optical probes (Hanson et al, 2007) which are based on the use of a fluorescent dye which is influenced by changes in pH and are of value for high-throughput process screening in miniature bioreactors (Demuth et al, 2016;Ge et al, 2006;Wu, Lin, Wang, Cui, & Cui, 2008). An unfortunate drawback of a pH probe in a bioreactor is the potential for pH probe drift and this requires confirmation by an off-line measurement method (Saucedo, Wolk, Arroyo, & Feng, 2011).…”