title: Easy to use and reliable technique for online dissolved oxygen tension measurement in shake flasks using infrared fluorescent oxygen-sensitive nanoparticles.
abstract: BACKGROUND
  Despite the progressive miniaturization of bioreactors for screening purposes, shake flasks are still widespread in biotechnological laboratories and industry as cultivation vessels. Shake flasks are often applied as the first or second step in applications such as strain screening or media optimization. Thus, there are ongoing efforts to develop online measurement techniques for shake flasks, to gain as much information as possible about the cultured microbial system. Since dissolved oxygen tension (DOT) is a key experimental parameter, its accurate determination during the course of experiment is critical. Some of the available DOT measurement techniques can lead to erroneous measurements or are very difficult to handle. A reliable and easy to use DOT measurement system, based on suspended oxygen-sensitive nanoparticles, is presented in this work.
  
  
  RESULTS
  In a cultivation of Kluyveromyces lactis, a new DOT measurement technique via suspended oxygen-sensitive nanoparticles was compared with the conventional DOT measurement via fixed sensor spots. These experiments revealed the main disadvantage of applying sensor spots. With further cultivations of Escherichia coli and Hansenula polymorpha, the new measurement technique was successfully validated. In combination with a RAMOS device, kLa values were determined during the presented cultivations. The determined kLa values are in good agreement with a correlation recently found in the literature.
  
  
  CONCLUSIONS
  The presented DOT measurement technique via suspended oxygen-sensitive nanoparticles in shake flasks turned out to be easy to use, robust and reliable under all applied combinations of shaking frequencies and filling volumes. Its applicability as an online monitoring system for cultivations was shown by means of four examples. Additionally, in combination with a RAMOS device, the possibility of experimental kLa determination was successfully demonstrated.
authors.affiliation: Biochemical Engineering, AVT-Aachener Verfahrenstechnik, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany. david.flitsch@avt.rwth-aachen.de.
authors.forename: David
authors.initials: D
authors.lastname: Flitsch
authors.affiliation: Biochemical Engineering, AVT-Aachener Verfahrenstechnik, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany. tobias.ladner@avt.rwth-aachen.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Ladner
authors.affiliation: Biochemical Engineering, AVT-Aachener Verfahrenstechnik, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany. mihaly.lukacs@rwth-aachen.de.
authors.forename: Mihaly
authors.initials: M
authors.lastname: Lukacs
authors.affiliation: Biochemical Engineering, AVT-Aachener Verfahrenstechnik, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany. jochen.buechs@avt.rwth-aachen.de.
authors.forename: Jochen
authors.initials: J
authors.lastname: Büchs
mesh_terms: D019149:Bioreactors; D002244:Carbon / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism; D005453:Fluorescence; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007259:Infrared Rays; D007716:Kluyveromyces / Q000187:drug effects / Q000254:growth & development; D053758:Nanoparticles / Q000737:chemistry*; D009862:Online Systems; D010100:Oxygen / Q000032:analysis*; D015203:Reproducibility of Results; D012995:Solubility
chemical_list: D049452:Green Fluorescent Proteins; D002244:Carbon; D010100:Oxygen