Real‐time pH monitoring of industrially relevant enzymatic reactions in a microfluidic side‐entry reactor (μSER) shows potential for pH control

• Published in: Biotechnology journal Vol. 12; no. 6
• Main Authors: Gruber, Pia, Marques, Marco P.C., Sulzer, Philipp, Wohlgemuth, Roland, Mayr, Torsten, Baganz, Frank, Szita, Nicolas
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 01.06.2017
• Subjects: Biocatalysis; Bioreactors; Catalysis; Enzyme Assays; Hydrogen-Ion Concentration; Kinetics; Lab-On-A-Chip Devices; Microfluidic Analytical Techniques - instrumentation; Microfluidic Analytical Techniques - methods; Microfluidics; Microreactor; Online monitoring; Optical sensor; Penicillin G acylase; pH sensor; Transketolase; Transketolase - metabolism; Optical sensor; Microreactor; Online monitoring; Transketolase; Penicillin G acylase; pH sensor
• ISSN: 1860-6768; 1860-7314
• DOI: 10.1002/biot.201600475

Monitoring and control of pH is essential for the control of reaction conditions and reaction progress for any biocatalytic or biotechnological process. Microfluidic enzymatic reactors are increasingly proposed for process development, however typically lack instrumentation, such as pH monitoring. We present a microfluidic side‐entry reactor (μSER) and demonstrate for the first time real‐time pH monitoring of the progression of an enzymatic reaction in a microfluidic reactor as a first step towards achieving pH control. Two different types of optical pH sensors were integrated at several positions in the reactor channel which enabled pH monitoring between pH 3.5 and pH 8.5, thus a broader range than typically reported. The sensors withstood the thermal bonding temperatures typical of microfluidic device fabrication. Additionally, fluidic inputs along the reaction channel were implemented to adjust the pH of the reaction. Time‐course profiles of pH were recorded for a transketolase and a penicillin G acylase catalyzed reaction. Without pH adjustment, the former showed a pH increase of 1 pH unit and the latter a pH decrease of about 2.5 pH units. With pH adjustment, the pH drop of the penicillin G acylase catalyzed reaction was significantly attenuated, the reaction condition kept at a pH suitable for the operation of the enzyme, and the product yield increased. This contribution represents a further step towards fully instrumented and controlled microfluidic reactors for biocatalytic process development. The pH is an important parameter for the efficiency of enzymatic reactions. Small volume flow reactors, also known as microfluidic reactors, can be used to optimise enzymatic reactions at low cost. Therefore, being able to measure the pH in a microfluidic reactor is very important. In this contribution the authors demonstrate that the measurement of pH in such a reactor is possible by integrating pH sensors at multiple locations. These sensors were used to measure the pH in two enzymatic reactions and it was shown that the pH could be adjusted to remain within boundaries ideal for the enzymes.