Journal articles, book contributions, reviews

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Singh, Sukhdeep; Schober, Andreas; Gebinoga, Michael; Groß, Gregor Alexander
ChemInform abstract: Convenient method for synthesis of thiazolo[3,2-a]pyrimidine derivatives in a one-pot procedure. - In: ChemInform, ISSN 1522-2667, Bd. 42 (2011), 44, insges. 1 S.
Köhler, Michael; Günther, Mike; Funfak, Anette; Cao-Riehmer, Jialan; Knauer, Andrea; Li, Shuning; Schneider, Steffen; Groß, Gregor Alexander
From droplets and particles to hierarchical spatial organization: nanotechnology challenges for microfluidics. - In: Journal of physical science and application, ISSN 2159-5348, Bd. 1 (2011), 3, S. 125-134

The compartimentation of fluids in the microliter, nanoliter and picoliter range leads recently to many applications of microfluidics in material development, diagnostics and biological screenings. Droplet-based microfluidics allows the improvement of nanoparticle homogeneity and the tuning of particle properties. It supports combinatorial synthesis of inorganic as well as organic substances and can be applied for the cultivation and screening of bacteria, eucaryotic cells and fish embryos. The well-ordered handling and the addressing of microfluid segments improves the information transfer between chemical, biological and electronic systems. Despite this remarkable technical progress, there is a particular importance of microfluidics for future nanotechnological solutions. The hierarchical spatial organization of liquids, particles and gels in microfluidics represents a fundamental biomimetic principle which overcomes the limits of planar technology and opens the gate for realizing complex structured threedimensional nanoarchitectures. Recent applications of microstructured fluids in chemistry and biology and concepts for future developments will be discussed.

Singh, Sukhdeep; Köhler, Michael; Schober, Andreas; Groß, Gregor Alexander
The Eschenmoser coupling reaction under continuous-flow conditions. - In: Beilstein journal of organic chemistry, ISSN 1860-5397, Bd. 7 (2011), S. 1164-1172
Abahmane, Lahbib; Köhler, Michael; Groß, Gregor Alexander
Gold nanoparticle-catalyzed synthesis of propargylamines: the traditional A3-multicomponent reaction performed as a two-step flow process. - In: Chemistry - a European journal, ISSN 1521-3765, Bd. 17 (2011), 10, S. 3005-3010
Boškovic, Dušan; Löbbecke, Stefan; Groß, Alexander; Köhler, Michael
Residence time distribution studies in microfluidic mixing structures. - In: Chemical engineering & technology, ISSN 1521-4125, Bd. 34 (2011), 3, S. 361-370

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.
Köhler, Michael;
Microtechnology in chemical engineering. - In: Chemical engineering & technology, ISSN 1521-4125, Bd. 34 (2011), 3, S. 330
Kürsten, Dana; Cao, Jialan; Funfak, Anette; Müller, Philipp; Köhler, J. Michael
Cultivation of Chlorella vulgaris in microfluid segments and microtoxicological determination of their sensitivity against CuCl2 in the nanoliter range. - In: Engineering in life sciences, ISSN 1618-2863, Bd. 11 (2011), 6, S. 580-587

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.
Köhler, J. Michael;
Editorial: microtechnology for life science applications. - In: Engineering in life sciences, ISSN 1618-2863, Bd. 11 (2011), 2, S. 116-117
Funfak, Anette; Cao-Riehmer, Jialan; Knauer, Andrea; Martin, Karin; Köhler, Michael
Synergistic effects of metal nanoparticles and a phenolic uncoupler using microdroplet-based two-dimensional approach. - In: Journal of environmental monitoring, ISSN 1464-0333, Bd. 2 (2011), 13, S. 410-415

A droplet-based microfluidic technique for testing multiple reagent concentrations is presented. We used this experimental approach to study combined effects of gold (AuNP) and silver nanoparticles (AgNP) with the phenolic uncoupler 2,4-dinitrophenol (DNP) with respect to the growth of Escherichia coli. In order to evaluate the toxicity of binary mixtures, we first encapsulated the E. coli cells and particle mixtures inside the microdroplets using PEEK (polyetherketone) modules. Two-dimensional concentration spaces with about 500 well separated droplets were addressed. We subsequently analyzed the cell growth, the viability and the autofluorescence intensity (metabolic activity) of the bacteria with a micro-flow-through fluorometer and photometer. Dose-dependent synergistic effects were found for the binary mixture of AgNPs and DNP, which indicated a stronger interaction in the mixture than it was expected from effect summation. For the binary mixture of DNP and AuNPs in non-toxic concentrations, we found only weak synergistic effects at low DNP concentrations. Furthermore, the non-toxic tested AuNPs causes effect summation in the binary mixture with the phenolic uncoupler. In general, we demonstrated the efficiency of a droplet-based microfluidic system for fast high-throughput screenings of binary and multiple mixtures. This work also confirmed the relevance of highly resolved droplet-based assays for the miniaturization of ecotoxicological aquatic test systems.