Publikationen

The residence time distribution (RTD) characteristics of three microreactors containing different passive mixing structures, namely, a three dimensional serpentine structure, a split-and-recombine structure and a staggered herringbone structure, were investigated and compared. An experimental input-response technique was applied which required deconvolution of the measured data by modeling of the RTD. The proposed technique provides useful information on optimized application and operation of microfluidic devices. The serpentine reactor and the split-and-recombine reactor show improvement in RTD behaviour, i.e., narrowing of RTD curves, at Re-numbers > 30 due to effective transversal mixing and therefore reduced axial dispersion. In the case of the staggered herringbone structure, dead volumes could be observed which considerably affect the RTD.

The cultivation of the monocellular green alga Chlorella vulgaris was implemented into microfluid segments to demonstrate the possibility of an automated screening of toxic effects of the common algaecide CuCl2. Therefore, the nutritional as well as light and carbon dioxide requirements of the algae had to be adapted to the microfluidic device. Generally, sequences of about 350 fluid segments with single volumes of about 500 nL were applied for the dose-response experiments. The growth of algae cultures inside microfluidic segments was noninvasively measured by microflow through techniques using two different optical channels. A multi-endpoint detection was realized by the photometric characterization of cell density by transmission measurements and the measurement of density of autofluorescent cells. The different methods revealed comparable half maximal effective concentrations (EC50) in the range between 34.6 and 39.9 mg/mL for the toxicity of CuCl2 to the green algae C. vulgaris. By reference experiments in microtiter plates lower EC50 were achieved presumably caused by increased alkalinity of the growth medium due to higher photosynthesis. The results show that the microsegmented flow technique is well suited for the automated determination of dose/response functions for microorganisms like C. vulgaris and for the application of multi-endpoint procedures at the nanoliter scale.