Optical sensor systems for bioprocess monitoring

Fluorescence spectroscopy is flexible for monitoring a number of analytes via direct or indirect correlations.

“The flexibility of fluorescence spectroscopy is well‐reported for the monitoring of a number of analytes, via direct or indirect correlations, such as proteins, vitamins, co‐enzymes, glucose, ethanol, ATP, pyruvate, nitrate, or succinate (Shaw et al., 1999; Ulber et al., 2003; Hantelmann et al., 2006; Glindkamp et al., 2009; Ranzan et al., 2012).”

NIR low absorption coefficients enable a higher penetration depth, allowing the use of NIR in solids or turbid liquids such as culture broths.

“The low absorption coefficients enable a higher penetration depth, allowing the use of this technique in solids or turbid liquids, such as culture broths (Marose et al., 1999; Ulber et al., 2003; Glindkamp et al., 2009; Henriques et al., 2010).”

Spectroscopic sensors do not interfere with biological material, allowing monitoring of in vivo cells and obtaining information on their intracellular state, in addition to information on extracellular media.

“Also, as non‐invasive techniques, spectroscopic sensors do not interfere with the biological material, allowing to monitor in vivo cells and obtain information on their intracellular state, in addition to information on extracellular media (Marose et al., 1999; Ulber et al., 2003; Hantelmann et al., 2006; Glindkamp et al., 2009).”

The main difficulties for the restricted application of optical sensors are interferences that influence the quality of fluorescence spectra, such as turbidity, gas bubbles, and fouling.

“The main difficulties described for the restricted application of this technology to date are mostly due to interferences that influence the quality of the fluorescence spectra, such as turbidity, gas bubbles, and fouling (Tartakovsky et al., 1996; Marose et al., 1999; Ulber et al., 2003).”

Raman spectroscopy cannot be used with strongly fluorescent samples.

“Nevertheless, the intensity of the signal acquired is very weak and difficult to separate from the scattering, and it cannot be used with strongly fluorescent samples (Ulber et al., 2003; Singh et al., 2019).”

UV/Vis has two major drawbacks: lack of specificity and can only be used in liquid and homogenous samples.

“This technique has two major drawbacks: the lack of specificity and can only be used in liquid and homogenous samples (Ulber et al., 2003; Claßen et al., 2017).”

Parameters measured online are usually less than the required parameters needed for accurate monitoring and control.

“Also, the parameters measured online are usually less than the required parameters needed for accurate monitoring and control (Ulber et al., 2003; Glindkamp et al., 2009).”

Spectroscopic optical sensors are non-invasive, non-destructive, and allow the detection of several molecules simultaneously.

“These sensors are non‐invasive, non‐destructive, and allow the detection of several molecules simultaneously.”