Characterization and application of an optical sensor for quantification of dissolved O2 in shake-flasks

On-line measurement of dissolved O-2 in shake-flasks was realized via immobilized sensor spots containing a fluorophore with an O-2-dependent luminescent decay time. An unaffected sensor signal during 80 autoclaving cycles suggests multi-usage of sensor equipped shake-flasks. The sensor had a response time of 6 s. Quantification of gas-liquid mass transfer revealed maximum k(L)a values of 150 h(-1), from which maximum O-2 transfer capacity of 33 mM h(-1) was calculated. Liquid volume and shaking frequency have a strong influence on k(L)a. Exemplified by cultivations of Corynebacterium glutamicum the importance of shaking rate for O-2 supply of bacterial cultures is shown. Sampling of microbial cultures with intermittent shaking of a few minutes can cause O-2 limitation. Based on the results of this work a simple and straightforward tool is now available for accurate O-2 sensing in shake-flasks, which are widely used in microbial cultivations.