E.E. Krommenhoek

Aerobic batch cultivation in micro bioreactor with integrated electrochemical sensor array

Aerobic batch cultivations of Candida utilis were carried out in two micro bioreactors with a working volume of 100 μL operated in parallel. The dimensions of the micro bioreactors were similar as the wells in a 96‐well microtiter plate, to preserve compatibility with the current high‐throughput cultivation systems. Each micro bioreactor was equipped with an electrochemical sensor array for the online measurement of temperature, pH, dissolved oxygen, and viable biomass concentration. Furthermore, the CO2 production rate was obtained from the online measurement of cumulative CO2 production during the cultivation. The online data obtained by the sensor array and the CO2 production measurements appeared to be very reproducible for all batch cultivations performed and were highly comparable to measurement results obtained during a similar aerobic batch cultivation carried out in a conventional 4L bench‐scale bioreactor. Although the sensor chip certainly needs further improvement on some points, this work clearly shows the applicability of electrochemical sensor arrays for the monitoring of parallel micro‐scale fermentations, e.g. using the 96‐well microtiterplate format.

Quantitative determination of glucose transfer between cocurrent laminar water streams in a H-shaped microchannel

To explore the applicability of a laminar fluid diffusion interface (LFDI) for the controlled feeding of microbioreactors, glucose diffusion experiments were carried out in a rounded H‐shaped microstructure etched in a glass substrate. The diffusion channel of the microstructure had a length of 4 mm and a depth of 50 μm with a trapezoidal cross section with a width of 100 μm at the bottom and 200 μm at the surface of the channel. The microchannel was operated at residence times of less than 1 s ensuring high‐mass‐transfer rates. It was confirmed, both by microscopic observations as well as computational fluid dynamics (CFD) studies that the flow characteristics in the microchannel were fully laminar. Special attention was paid to flow splitting at the end of the channel, because the CFD simulations indicated that the performance of the device was sensitive to unequal flow splitting. The difference in outflow volume of the two streams was measured to be small (1.25% ± 0.6%). The measured glucose concentration in both exit ports at a fixed residence time was found to be stable in time and reproducible in multiple experiments. CFD simulation was shown to be a powerful tool for estimating the mass transfer in the LFDI, even at very short residence times. The results obtained in this work show the applicability of LFDI for the controlled diffusive supply of a solute to a water stream, with as possible application substrate and/or precursor feeding to microreactors.