MCR 2 x 8

Sensor Block Development for Biochemical Engineering

MCR, sensor block for O2/pH monitoring in mL-scale bioreactors

This project was initiaded by the Technical University Munich, the Institute of Biochemical Engineering. The goal was to develop an effective production procedure using recombinant microbial strains for enantioselective catalysis. As numerous screening experiments were necessary the design of a new tool for bioprocess development was initiated. PreSens´ role was creating an online DO and pH monitoring device for 48 ml-scale vessels. This new  technique would allow performing up to 48 automated DO and pH controlled experiments in parallel stirred tanks.

Specifications

The main specific challenges for the sensors were

  • the fermentation process should not be affected in any way
  • the sensors needed to be stable with radiation
  • they needed to be robust as they might be used for a longer fermentation period or at a very high stirring rate
  • all sensors from one series needed to have the same calibration data
  • a scalable production process had to be developed for high quantities of disposables

The main specific challenges for the new transmitter were

  • pre-calibrated channels and
  • the option for a one-point calibration
  • robust to harsh environment
  • communication via RS485 interface

Implementation

New transmitters were engineered to read out the 48 DO and pH sensors. To be more flexible for different formats the whole monitoring set-up consisted of 6 small units with 8 x 2 optical modules, interfaced by robust RS485 standard. The communication protocol was established in close cooperation to partners doing hard- and software design. As the typical working environment of this device can be challenging the housing and adapters were designed according to IP 64 (DIN EN 60529 / DIN 40 050). 

The sensing materials were integrated in disposable stirred bioreactors made of polystyrene. They form two small sensor spots on the inside vessel wall, for pH and oxygen respectively.

Production & Validation

As soon as prototypes of the new pH sensors and the respective transmitters were constructed, it was necessary to examine different sensor patterns regarding biocompatibility, mechanical robustness and calibration characteristics. Special attention was paid to cross sensitivity to media components or fermentation products.