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## Über dieses Buch

Microreaction technology is the logically consistent application of microsystem techniques in chemical reaction and process engineering. Miniaturization in this field is the strategy of success and requires the development of small, inexpensive, independent and versatile chemical reaction units. Microreaction technology is at present regarded as one of the fastest evolving and most promising disciplines in chemical engineering, combinatorial synthesis and analysis, pharmaceutical drug development and molecular biotechnology. A broad range of microstructurable materials is a prerequisite for microreaction technology and the development of microreactors goes hand in hand with the availability of a number of modem, versatile microfabrication technologies. Today, it is possible to manufacture tbree­ dimensional microstructures, almost without any restrictions with regard to design and choice of suitable materials, for various chemical applications -just in time to support the development of functional units for microreactors, e. g. micromixers, micro heat exchangers, micro extractors, units for phase transfer, reaction cham­ bers, intelligent fluidic control elements and microanalysis systems. The advantages of microreactors, e. g. the use of novel process routes, the re­ duction of reaction byproducts, the improvement of 'time to market', the high flexibility for all applications requiring modular solutions, have had a strong im­ pact on concepts of sustainable development. Many of the leading companies and research institutes in the world have recognized the tremendous possibilities of microreactor concepts and of their economic potential, and have thus initiated worldwide research and development activities.

## Inhaltsverzeichnis

### Reaction Engineering for Microreactor Systems

Finite element simulations of two-and three-dimensional fluid flow, thermal fields, and chemical species concentrations in microfluidic devices are presented as a means for obtaining accurate predictions of microreactor performance. The chemical reaction engineering methodology is illustrated with case studies of a prototype microreactor for partial oxidation reactions. Platinum catalyzed ammonia oxidation serves as a demonstration chemistry. The reactor simulations are in excellent agreement with experimental observations. The results also mirror observed ignition-extinction behavior by revealing that ignition occurs downstream and the reaction front subsequently travels upstream due both to heat conduction and the presence of fresh reactants upstream. The utility of the simulation strategy in the design of microfluidic devices for chemical reactions is exemplified with a case study of placement of thermal shunts to control the shape of the reaction front.

K. F. Jensen, I-Ming Hsing, R. Srinivasan, M. A. Schmidt, M. P. Harold, J. J. Lerou, J. F. Ryley

### Observations on Hypothetical Miniaturised, Disposable Chemical Plant

Since the author proposed the concept of a miniaturised plant in 1993 [1] a number of developments have taken place in terms of both experimental evaluation and concepts.We briefly review the original idea of the miniature plant, and discuss how ideas on the miniaturisation of one candidate process, hydrogen cyanide, have developed.A somewhat different concept, that of the disposable miniature batch plant is also discussed, and finally a hypothetical semibatch process for the manufacture of hydrogen fluoride is described.

Jack W Ponton

### Monolithic Microreactors Possessing Regular Mesopore Systems for the Succesful Performance of Heterogeneously Catalysed Reactions

Microreactors represent a novel approach for chemical processing. In this study a monolithic microreactor having channels in micrometer dimension and regular pores in nanometer scale has been developed. The microreactor was tested in the partial hydrogenation of cyclododecatriene to yield cyclododecene. In addition, several particle bed reactors were tested, in order to establish advantages and the superiority of the monolithic microreactor.

G. Wießmeier, K. Schubert, D. Hönicke

### Scouting Study About the Use of Microreactors for Gas Supply in a PEM Fuel Cell System for Traction

An electric propulsion system with a methanol reformer, a catalytic burner, a gas cleaning unit and Proton-Exchange Membrane Fuel Cells (PEMFC) is described. Based on experimental data for methanol steam reforming criteria are developed for a microreactor system.

R. Peters, H.-G. Düsterwald, B. Höhlein, J. Meusinger, U. Stimming

### Solute Transfer by Liquid / Liquid Exchange Without Mixing in Micro-Contactor Devices

Transport properties within fluids at sub-millimetre dimensions in micro-engineered systems tend to be dominated by laminar flow, diffusion, and surface tension effects. Design, fabrication and operation of micro-chemical reactors is enhanced by an understanding of these processes aided by application of CFD modelling.Micro-fabricated channels carrying single phase solutions are shown to exhibit solute transport under diffusion control demonstrated by monitoring acid/base reaction.The principles of diffusive transfer in micro scale fluid flows have been extended using innovative micro-contactor device designs whereby immiscible fluids flow in contact without mixing but allowing rapid transfer of solute between the fluids.Micro-contactors with ~30 to 100 µm wide channels have been operated for liquid/liquid extraction processes with a range of critical geometries and flow conditions. Transfer of test solute FeIII between aqueous and organic phases has been achieved reliably within micro-contactors without the need for solvent mixing and separation stages. Observed flow stability and measured solute transfer rates are consistent with models for interface position and diffusion control of solute transfer across laminar flows. Analysis of the data shows extraction rates are consistent with diffusion coefficients of ~3 × 10−10 m2s−1.

I. Robins, J. Shaw, B. Miller, C. Turner, M. Harper

### Reactions in Microreactors in Electric Fields

Microreactors have been used for investigation of spatio-temporal concentration patterns arising due to interaction of specific complex reactions with transport of reaction species by molecular diffusion in spatially distributed reaction media. Propagating reaction fronts form one class of these patterns which are of interest in many areas of fundamental research. Particular interest is devoted to studies of effects of external fields (electrical and gravitational) that initiate other transport processes like electromigration of ionic components and hydrodynamical flow.

H. Ševčíková, D. Šnita, M. Marek

### High-Temperature Micro Catalysis: a New Design for Comparative Reaction Studies in Technical and Model Systems

We present a system for studying heterogeneously catalytized gas phase reactions on single-crystal surfaces. As a model reaction we studied the high-temperature dehydrogenation of methanol to formaldehyde and furtheron to CO. A new flow microreactor was developed in which a radial gas flow is run over the surface of a single-crystal sample. Residence times can be kept as short as 10−3 s opening up the same time scale as in the technical flow reactor

M. Bender, A. Knocks, S. Hövel, H.-J. Freund

### Micro-Structure Electrodes as Electronic Interface Between Solid and Gas Phase: Electrically Steerable Catalysts for Chemical Reactions in the Gas Phase

The application of Micro-Strip Electrode (MSE) structures as electrically steerable catalysts to induce chemical reactions in gases is investigated. It can be shown that, depending on the geometry, the electric field strength, and the gas pressure in the MSE reactor, chemical reactions can be ‘switched on’ and ‘off’ by applying a moderate voltage (several 100 Volt). Due to the micro-structure dimensions already at these voltages electrons with mA / cm2 current can be emitted from the solid to the gas phase without observable heating of the electrodes. The emitted and then accelerated electrons induce in an electrically steerable manner dissociation with subsequent chemical reactions via radical formation. Since a large number of final product molecules is generated per released electron, the MSE act as dynamical catalysts. The gas phase near the MSE surface contains two constitutents: very hot electrons inducing molecular excitation and fragmentation, and rather cold radicals, molecular fragments, ions and gas molecules at a temperature externally selected for the synthesis process. The MSE reactor provides thus a two-temperature system at a wide presure range, where the temperatures for molecular dissociation and synthesis can be chosen independently from each other. First stimulating results and possible areas of application are discussed.

M. Roth, T. Haas, M. Lock, K. H. Gericke, A. Bräuning-Demian, L. Spielberger, H. Schmidt-Böcking

### Fabrication of Components and Systems for Chemical and Biological Microreactors

Advances in the development of different microfabrication technologies have by now enabled a status where the industrial fabrication of threedimensional microstructures is possible almost without restrictions in design or material. Microfabrication tools like dry and wet etching processes, LIGA technology, structuring of photosensitive glass, laser micromachining, micro spark erosion as well as improved processes of precision engineering like micro milling enable a cost effective mass production of microreactor components if they are combined with replication techniques like injection molding. The outstanding meaning of these technologies, in particular for their use in chemistry and biotechnology, is that they offer the threedimensional structuring of a wide variety of materials such as metals, polymers, glasses and ceramics. Numerous microreactor components are presently available on a prototype stage, e.g. micromixers, microextractors micro reaction chambers, miniaturized heat exchangers, membrane units and micropumps. All these devices can easily be combined to microreactors adapted to the specific purpose of the respective chemical reactions. In addition, a number of micro- and nanosensors as well as sensor arrays exist which can be integrated into microreaction systems for process control or parallel analysis in high throughput screening.

W. Ehrfeld, Cl. Gärtner, K. Golbig, V. Hessel, R. Konrad, H. Löwe, Th. Richter, Ch. Schulz

### Technologies and Microstructures for (Bio)chemical Microsystems

There is a strong correlation between microreactors and microsystems for chemical and biochemical analysis. Microreactors need to be closely coupled to analysers, whereas in micro analysis systems a microreactor is often an important element. An example of a device that can be considered both as microreactor and as analyser, a catalytic gas sensor is presented. In particular the role of porous silicon material for fabrication and as support for the catalyst is shown. A modular concept for fabrication of micro analysis systems is illustrated with some components. A new capacitive pressure/flow sensor is presented with low power operation and a detection limit of 6 nl/s. Microchannels play an essential role in many micro analysis systems. Simulations made using the Flow3D programme based on the incompressible Navier-Stokes equations, give guidelines for the construction of the flow channel and positioning of sensors whereas the effects of the channel geometry on the profile of the injected plug can be predicted. Finally, a number of different techniques is presented to produce closed microchannels in silicon. Particular attention is paid to techniques that enable the fabrication of electrically insulating microchannels, which are of particular interest for capillary electrophoresis (CE) applications

Albert van den Berg, Eelco van Akker, Edwin Oostenbroek, Willem Tjerkstra, Istvan Barsony

### Functionalized Biomolecular Membranes for Microreactors

Functionalized membranes are interesting components for the control of mass flow and chemical reactions in microreactor systems. In the paper it will be shown that biomolecular membranes with characteristic dimensions larger than several micrometers can be applied successfully as templates for manufacturing of such microcomponents. The preparation of membranes with a highly ordered nanopore distribution will be studied. For that, two-dimensional bacterial surface layer (S-layer) proteins can be used as a template. S-layer exhibit different kinds of lattice symmetry with spacings of the morphological units in the range between 10 and 30 nm, and possess pores of identical size in the range below 6 nm. Some of them show remarkable mechanical and chemical stability. S-layer sheets were isolated from Sporosarcina ureae. The lattice constant of the 2D protein crystal equals 13.2 nm measured with atomic force microscopy. This 2D crystal has been used as a template for the preparation of metallized membranes. The metal was deposited in different ways, via vapour phase by pulsed laser deposition, and via liquid phase. The deposition of platinum, platinum/carbon, palladium and nickel will be reported. Depending on the amount of template coverage with metal, various kinds of functionality of the membrane can be achieved. Pulsed laser deposition offers the possibility to produce ultrathin patterned metal films. Under the condition of incomplete coverage of the template selective decoration of the proteins has been observed. Deposition of platinum or palladium clusters from the aqueous solution is characterised by selective adsorption on the protein surface. It allows the preparation of nanodisperse catalyst particles, arranged with a high geometrical order and surface density at the biomolecular membrane.

Wolfgang Pompe, Michael Mertig, Remo Kirsch, Harald Engelhardt, Thomas Kronbach

### Nano Titer Plates: Micro Compartment Arrays for Biotechnological Applications

Arrays of micro compartments for combinatorial chemistry and biotechnological applications have been fabricated by means of photolithography and anisotropic chemical wet etching. Integration levels of 16′000 per 4″ wafer have been achieved. Optically transparent membranes or micro sieves allowing for rinsing between process steps can be incorporated. For the investigation of thermally activated biochemical reactions a micro compartment array with integrated thermo control has been developed, which allows the adjustment of thermal gradients over a 4″ wafer. Peak temperatures exceeding 90 °C at the center of the wafer as well as temperature gradients with ΔT = 40 °C could be demonstrated. To avoid fluidic crosstalking between adjacent compartments a technique has been developed, that allows selectively hydrophobizing the rims of the compartments.

Günter Mayer, Jens Tuchscheerer, Thomas Kaiser, Klaus Wohlfart, Eugen Ermantraut, J. Michael Köhler

### An Automated Method to Create a One Dimensional Array of Chemically Synthesized Oligonucleotides

In this paper we describe a method to synthesize a variety of different oligonucleotides in a quasi parallel procedure on the surface of a polypropylene tape. The relation between necessary chemical coupling steps n and thus generated oligonucleotides m with a length of e.g. 15 monomers is: m = n − 14. To get a high synthesis throughput and the possibility of an overnight run, the system has been fully automated. To start the synthesis, only the desired sequence programming is necessary without further control of the system.

R. Bader, O. Betz, H. Brugger, M. Hinz, C. Rembe, E. P. Hofer, H. Seliger

### Development of a Microreactor for Chemical Production

The technology needed to produce structures at micro scales has improved significantly over the past few years. This has opened up new opportunities for engineering compact, efficient fluid flow systems on a micro scale. Small channels created within the microprocessors automatically involve very short diffusion, conduction and mixing path lengths, so that mass, heat and momentum transfer rates are extremely high. This allows microreactors to be produced which exert close control over stream temperatures and compositions, even for very rapid reactions. A further benefit of microengineering will come from the ability to integrate the control devices and sensors into a single unit and the combination of different units into a complete compact chemical processing system. Ultimately microengineering is another arm of process intensification and as such should considerably enhance the reduction of plant size and the improvement of plant safety.

J. R. Burns, C. Ramshaw, A. J. Bull, P. Harston

### Laser Processes for Flexible Manufacturing of Fluidic Micro Reactors

Remarkable features of ceramic materials are the high hardness and the high corrosion resistance. These properties are highly appreciated by application, but pose serious problems in respect to machining. This difficulty can be overcome by laser machining. Hard and brittle materials like ceramics or temperature sensitive materials like polymers can be machined with precision in the µm-range. Laser technology has been applied for manufacturing of micro-scale components in electronics and micro systems technology. Laser-assisted etching of read/ write heads for hard discs /1/, drilling of vias in printed circuit boards /2/, or drilling of ink jet nozzles for printer heads /3/ has been proven as reliable techniques. The experience in production technology gained there could be easily transferred to the production of micro-scale fluidic or mechanical devices. Depending on requirements, nearly all materials could be structured by laser radiation. In the following, examples for laser machining will be given.

A. Gillner, M. Wehner, D. Hellrung, R. Poprawe

### The Use of Microcapillaries and Catalytic Contact Printing for the Preparation of Microstructured Magnetic Surfaces and for the Ordered Deposition of Proteins on Surfaces

During the last 5 years Whitesides (1–4) described 2 elegant methods for the chemical surface heterogenisation resulting in well defined surface patterns of µm dimensions. The methods known as µ-printing or µ-capillary extrusion start with the preparation of a master structure which is e.g. prepared in silica by conventional photo- or electron lithography followed by silica etching. These structures are replicated in a flexible poyldimethylsiloxane stamp which may be used a)as a stamp (Fig. 1) to transfer a suitable chemical compound (“ink”) to a surface by direct contact of the “ink” to the surface to be modified orb)as a microcapillary system formed by the groves of the stamp in contact with a smooth surface.

H.-G. Braun, Th. Kratzmüller, E. Meyer

### Fabrication and Interconnection of Ceramic Microreaction Systems for High Temperature Applications

Mass and heat transfer are significantly enhanced in microreactors because of the large surface-to-volume ratio [1–4]. These effects are expected to strongly influence different types of reactions, in particular high temperature gas phase reactions in the field of heterogeneous catalysis [5,6] and highly exothermic, fast two- or three-phase reactions. The extreme temperature conditions and the high reactivity of the process gases in case of heterogeneous catalysis or of the process liquids in case of gas/liquid reactions seriously limits the number of micromaterials to be applied to ceramics, stainless steel or special alloys. Ceramic components may be mainly applied as supports for catalysts as in large-scale reactors. Furthermore, their low thermal conductivity may be favourably used to prevent undesired heat transfer by creating insulating barriers between hot and cold miniaturized components in compact microreaction assemblies.

V. Hessel, W. Ehrfeld, H. Freimuth, V. Haverkamp, H. Löwe, Th. Richter, M. Stadel, A. Wolf

### Fabrication of Microreactor Components by Electro Discharge Machining

Electro Discharge Machining (EDM), a well introduced technology for the processing of all kinds of conductive materials independent of the mechanical characteristics, has recently been extended to the micro-scale (µ-EDM). µ-EDM opens up a new entry to the microstructuring of materials like stainless steels for microreactor purposes. Here, the use of several µ-EDM techniques as well as their applications in microreaction technology are reported.

Th. Richter, W. Ehrfeld, A. Wolf, H. P. Gruber, O. Wörz

### Silicon Microreactors made by Reactive Ion Etching

This work presents the detailed description of the formation process of the silicon microreactors and micromechanical structures which will dominate the near future. The description is based mainly on the author’s experience and includes a description of the dry etching of silicon by means of different halogen plasmas. The well established methods of microsystem technology allow the cheap and fast production of silicon based microtools in large numbers via batch processing.

I. W. Rangelow, R. Kassing

### Porous Silicon as the Carrier Martix in a Micro Enzyme Reactor to Achieve a Highly Efficient and Long-Term Stable Glucose Sensor

Porous silicon with its spongious structure and vast surface enlargement was investigated as the carrier matrix for immobilised enzymes in micro enzyme reactors.The microreactors were micromachined, in (110) silicon (p-type, 20–70 Ω.cm) by anisotropic wet etching, giving a parallel trench structure comprising 32 channels, 50 µm wide, spaced 50 µm apart and 250 µm deep. The surface enlarging porous layer on the reactor structures were achieved by anodising the reactors in a solution of hydrofluoric acid and ethanol. In order to evaluate the surface enlarging effect of different pore morphologies, the anodisation was performed at three different current densities, 10, 50 and 100 mA.cm−2.Glucose oxidase was coupled to the surface of the porous microreactors and a non porous reference reactor. The enzyme activity of the microreactors was recorded and compared with the non-porous reference reactor.Long-term stability measurements of glucose oxidase coupled to a planar porous silicon surface were performed. The porous layer was achieved on a (111) silicon sample; epilayer, n on n+ (6.8–9.2 Ω cm on 0.0015 Ω cm), anodised at 100 mA.cmℒ2 for 5 minutes.The studies of the glucose turn-over rate in the different micro reactors clearly demonstrated the surface enlarging effect of porous silicon as an enzyme carrier matrix. An increase in enzyme activity by a factor of 100, compared to the non porous reference, was recorded for the reactor anodised at 50 mA.cm−2. The results also establish the possibility to fabricate porous silicon on high aspect ratio microstructures.The long-term stability measurements displayed a high storage stability of the porous silicon carrier matrix, 2% loss after 5 months refrigerated storage. Steady state glucose loading (0.5 mM) of the GOD activated porous matrix showed a loss in enzyme activity of 56% over 4 days.

Johan Drott, Kjell Lindström, Lars Rosengren, Thomas Laurell

### MCR X. Important Aspects for Automating Preparative Chemistry

Usually, classical syntheses from n starting materials require sequences of at least n−1 preparation steps including separation and purification of the intermediates. A perfect alternative for the rapid synthesis of a large variety of chemical products are one-pot syntheses by multicomponent reactions (MCR)[1][2] based on the isocyanides. Between four and seven different types of reactants (educts) are mixed in a reaction vessel to form a product that contains at least one part of each educt. The educts and intermediates equilibrate and a stable product results, often with quantitative yields, in the final practically irreversible step involving the isocyanide. Reactions of this type are widely used for combinatorial chemistry. The minimisation of such syntheses and the computer-assisted handling of the results offer the chance of automating preparative chemistry.

Ivar Ugi, Michael Almstetter, Bernhard Gruber, Alexander Dömling

### MCR XII. Efficient Development of New Drugs by Online-Optimization of Molecular Libraries

The principles of combinatorial chemistry accelerate the development of new drugs enormously. Molecular libraries on the basis of multicomponent reactions (MCR) in liquid phase provide products of high diversity. Automated parallel synthesis and automatic analysis units (e.g. HPLC) provide the chance for optimizing the reaction conditions in an efficient way. Multi-parameter optimization by means of the genetic algorithm or other heuristics induce better yields at higher selectivity. The computer aided syntheses of molecular libraries under optimized reaction conditions with quality control results in an automaton, where the drug designer has the only but important task to choose the most useful starting compounds and thereby the molecular sub-space of a MCR.

Ivar Ugi, Michael Almstetter, Bernhard Gruber, Martin Heilingbrunner

### MCR XI. Microreactors as Processors for Chemical Computers

Computer chemistry as well as the newer research in computational chemistry try to predict or estimate reaction pathways. To date this kind of syntheses planning has not succeeded, nor did approaches using rule-based heuristics like so-called expert systems. The reason for this is that reacting compounds are a highly parallel system. Molecules of the same chemical compound will react in different ways and/or at a different moment. Too many parameters are responsible for how chemical reactions proceed. Computers can not follow chemical reactions. Up to now, the only way to handle chemical problems is to use the chemistry itself. Usually synthetic chemists are interested in the main product exclusively. Naturally they do not care too much about side reactions and other strange things going on in their reaction vessels. But this complexity of chemical reactions can be useful for solving problems for which computers are far too slow.Chemical reactions may be considered as mathematical functions. They have parameters like starting compounds, temperature, concentration or time. In a mixture of one mole of each of the reacting compounds you will find one mole functions.There is a class of problems in computer science that is called NP-complete. For problems belonging to this class no algorithms exist to solve the problem within acceptable time. A solution is to involve a highly parallel system of problem solv-ing functions like the syntheses of libraries of multicomponent reactions. It seems that the best way to calculate or simulate chemistry is chemistry itself, and instead of using computers to solve chemical problems, chemistry may solve problems of computer science.In order to make such a project possible, well-controlled chemical systems are necessary. Such apparatus covers one or more microreaction units, automatic detection units and a feedback unit for the syntheses control. An example for optimization using a chemical genetic algorithm will be presented. This involves a variable set of microreactors running parallel and a compound detection unit.

Bernhard Gruber, Michael Almstetter, Martin Heilingbrunner

### Microfabricated Devices for Performing Chemical and Biochemical Analysis

There is growing interest in microfabricated devices that perform chemical and biochemical analysis. The general goal is to use microfabrication tools to construct miniature devices that can perform a complete analysis starting with an unprocessed sample. Such devices have been referred to as lab-on-a-chip devices. Initial efforts on microfluidic laboratory-on-a-chip devices focused on chemical separations. Several laboratories have reported over the past few years on devices microfabricated using planar glass substrates for performing capillary electrophoresis [1,2,3,4,5,6,7,8,9]. Microchip devices have been demonstrated that perform open channel electrochromatography [10], and micellar electrokinetic capillary chromatography [11]. Micromachined glass substrates have also been used for the separation of DNA fragments [12, 13]. These miniature devices have shown performance either equivalent to or better than conventional laboratory devices in all cases investigated. For example, injection performance with the microfabricated devices has been observed to be one to two orders of magnitude more reproducible than with conventional capillary electrophoresis with 100 pL volumes. Other miniature chemical analysis devices that have recently been reported include flow injection analysis [14, 15, 16] and biosensors [17].

J. M. Ramsey, S. C. Jacobson, R. S. Foote

### A New Design of a Wafer Based Micro Reaction System

A new design of a wafer based micro reaction system is introduced. Main advantage of the system is that dead volume free valves are integrated on the wafer. Aggressive chemicals can be delivered in sub micro liter amounts with no cross contamination between the chemicals. The system is suitable for several applications in biochemistiy or environmental measurements, such as derivatisation, amino acid and carbohydrate analysis and microsequencing of proteins and nucleic acids. Automation of several processes is possible. The reaction chamber can take solid as well as liquid samples.

Christian Wurzel, Brigitte Wittmann-Liebold

### A Silicon Microreactor for Ulmmunological Applications

A silicon microreactor is presented, which was developed for the application in heterogeneous immunoassays such as the Enzyme Linked Immunosorbent Assay (ELISA). The device is realized in <100> silicon as a single channel and with fluid connections on one side to achieve an easier handling in comparison to other, already existing designs. The performance of the microreactor is demonstrated with T-2 toxin as a model analyte. In this application the microreactors showed a high sensitivity, short analysis times and the capability of repeated regeneration.

Peter Woias, Martin Richter, Uta v. Schoenebeck, Erwin Yacoub-George, Hans Wolf, Thomas Abel, Sabine Koch

### A Microfow Reactor for Two Dimensional Investigations of In Vitro Amplification Systems

For experimental spatially resolved studies in molecular evolution an open two dimensional reactor was designed which allows the continuous influx of reactants, homogeneous flow through the active reaction layer and the removal of reaction products. It is implemented in closed microstructured layers to allow flow control, conserve material and avoid contamination. Non-linear molecular amplification kinetics can induce spatial species distributions which change the nature of the selection process. This new approach unites the insights of ecological field studies with the precision of in vitromolecular evolution. We believe that this kind of study will open up the way to a better understanding of how optimisation proceeds at the molecular level. The design of the reactor is presented along with the experimental set-up and first results in a precursor single layer reactor.

Kristina Schmidt, Petra Foerster, Arne Bochmann, John S. McCaskill

### Flourescence Correlation Spectroscopy (FCS), the Detection Method for Sub-Microliter Miniaturized Biological Assays

The measurement of biochemical interaction in very small volumes has recently become a key issue in biotechnological applications in such fields as the life sciences, agriculture, ecology, to name but a few. The cost of biochemical substances in macroscopic amounts, not to mention their scarcity, is one of the driving forces behind the need to miniaturize of sample preparation, handling and analysis. Moreover, recently developed, massively parallel experimental approaches, such as combinatorial chemistry or evolutionary strategies, employed in the search for active compounds contribute to the need for miniaturization. The sheer number of similar samples, often surpassing 100,000 samples per batch, prohibits a macroscopic approach. Another field which is presently subject of a combinatorial explosion of numbers is genomic science. Here hybridization of oligomers for sequencing or comparison purposes is carried out in massively parallel approaches.

Karsten Henco

### The Physiocontrol-Microsystem (PCM): Analysis of Cellular Behaviour for Biomedical Research

Microsensors provide instruments particularly suited for the noninvasive analysis of cell and tissue cultures. Their outstanding benefit is the passive behaviour of continuously working transducers, which allows the dynamic recording of function-specific cellular processes. The microsensor system presented is a modular arrangement of various planar and non-planar sensor elements arranged in small cell culture chambers. An optic access to the cultures (e.g. for high resolution light microscopy and spectro-photometric techniques) enables a parallel and comparative data acquisition. The system was originally designed for biomedical research in chemotherapy and pharmacology but it turned out to be an effective device for toxicological and environmental research as well.

Martin Brischwein, Werner Baumann, Ralf Ehret, Michael Kraus, Mirko Lehmann, Bernhard Wolf

### Development of a Pharmacological Test System in a Miniaturized Hollow Fiber Bioreactor

Pharmaceutical usage in vitro has a long proving history. Common drug response assays do not always correlate with in vivo-like drug resistance and sensitivity. In contrast, tree-dimensional tissue cultivation in miniaturized hollow fiber bioreactors (mHFBR) do, indicating that drug response is a function of tissue architecture 1. Establishing a test system in vitro, feasible for theurapeutic drug monitoring (TDM), will considerably improve individual patient care, especially in leukæmia therapy, e.g. B-CCL, CML. For detecting drug effects, suitable sensors have to be found, thereto the sensors have to be so small to enable the integration in the HFBR. We emphasize on monitoring interbolism parameter, e.g. direct oxygen consumption and the NAD(P)H content, utilizing optical microsensors. In the study, we present a successful drug monitoring on a human bone marrow long-time (14d) cultivation exposed to a new biopharmaceutical drug for clinical usage, GM-CSF in combination with IL-3.

H. Maerz, R. Buchholz, F. Emmrich, L. Pfeiffer, U. Marx

### A Microreactor with On-line Mass Spectrometry for the Investigation of Biological Kinetics

A thermostated, stirred reactor of 14 mL volume with integrated pH-probe and control, mass spectrometer membrane probe and dosimeters was constructed. It allowed the measurement of gas exchange rates in anaerobic and aerobic systems together with the acid consumption or production rates. The accumulation of gases can be measured very sensitively, allowing short term measurements. This is particularly interesting for slowly growing organisms. Because of the small volume, studies with isotopes (e.g., 13C, 2H) become affordable. Kinetic experiments can be batch, continuous or fed-batch with stepwise or continuous feeding. Acetate and formate kinetics in mixed cultures were studied and kinetic models could be developed. In cultures of mammalian cells producing monoclonal antibodies, oxygen uptake and CO2 production rates were measured.

E. Heinzle, B. Meyer, A. Oezemre, I. J. Dunn

### Microarray Based Ligand Binding System

Based on Roger Ekins’ “Ambient Analyte Conditions” theory, a system has been developed that facilitates the simultaneous determination of tens of analytes on a miniaturized chip.

Udo Eichenlaub, Hans Berger, Peter Finckh, Hans Karl, Roger Ekins

### Advantages Afforded by Miniaturization and Integration of DNA Analysis Instrumentation

Miniaturization of chemical reaction chambers, along with the integration with low-cost detection components for real-time product quantification allows for significant improvements in instrumentation. Bulk chemical reactions can benefit from increased control at the microscopic level, according to the general volumetric reaction formula:$$Q\, = \,1/U\int_{qr} {dU}$$ where, Q is the volumetric reaction rate (moles/time · volume), U is the volume, and qris the “point” reaction rate at a “microscopic” volume unit. This equation is only valid if everything is uniform at a microscopic scale, that is, the reaction is working equally at all points. This uniformity is difficult to maintain, especially in reactions that have: 1) multiple co-reactants, 2) narrow and uniform condition (i.e., (temperature and pH) requirements, 3) macromolecular biological components, such as enzymes, and 4) diffusion limiting conditions. Typically, bulk bioreactors require significant effort to maintain such uniformity and often are difficult to scale up as a result. Arrays of miniaturized reactors with individual control can replace the less effective bulk systems, provide better uniformity, and therefore increase productivity.

M. Allen Northrup, Bill Benett, Dean Hadley, Paul Stratton, Phoebe Landre

### Nanoscaled Impedimetric Sensors for Multiparameter Testing of Biochemical Samples

In this contribution, the development of a nanoscaled interdigitated electrode structure for impedimetric measurements, made by deep U.V. lithography is reported. This biochemical impedimetric detection system has several potential advantages over other detection systems and is easy to integrate in a multiparameter testing system.

Peter Van Gerwen, Anca Varlan, Guido Huyberechts, Maaike Op De Beeck, Kris Baert, Willy Sansen, Lou Hermans, Robert Mertens

### Temperature Controlled Chip Reactor for Rapid PCR

Micro system technology offers new possibilities in the realization of miniaturized chemical devices. A miniaturized thermocycler was developed using thermal simulation and micromachining for preparation of the silicon chip. This device integrates a sample chamber etched in single crystalline silicon, a thin film heater and thin film temperature sensors. An external circuit allows the fast and precise thermal control at high heating and cooling rates with small power consumtion. In this device PCR experiments were performed successfully.

S. Poser, T. Schulz, U. Dillner, V. Baier, J. M. Köhler, G. Mayer, A. Siebert, D. Schimkat

### Incremental Parallel Microtitration: A Novel Approach Towards Test Strip Devices of Extreme Accuracy

The paper presents a novel approach of a microchemical on site test based on a high resolution volumetric analysis with optical equivalence indication. This novel microsystem combines the advantages of volumetric analyses with dry chemistry and microtitration techniques resulting in a short analysis time in combination with an extremely high accuracy. In comparison to other analytical methods a calibration of the system and a colour relation with a reference scale is not necessary. Furthermore there is no need to use any additional chemical reagents. The system is easy to handle and free of interferences. As mass production technologies can be applied the costs for manufacturing can be decreased dramatically.The variety of applications of this new analytical technique based on the incremental parallel microtitration will be presented showing first examples of acid base-, redox-, complexometric titrations and an outlook on the determination of more complex sum parameters like the chemical oxygen demand (COD) or the total organic carbon (TOC).

K. Cammann, C. Hilker, B. Roß, F. Zuther

### Concepts of Miniaturized and Fast GC and HPLC Analytical Systems Integrated in Microreactors

Requirements of an analytical system for the analysis of the products of ethenoxide and propenoxide synthesis are discussed in relation to the specific features of the microreactor technology. A selection of suitable stationary phases and column techniques are considered and preliminary results on the analysis of synthetic mixtures of compounds of ethenoxide synthesis are presented.

Alexander A. Kurganov, Klaus K. Unger

### Possibilities for Thermophysical Reaction Monitoring in Microreactors

Heat power measurements are interesting for the monitoring of the extent of chemical reactions, because it is a direct measure of this extent. In many cases analytical reactions including reactants or products of the reaction under investigation are monitored calorimetrically. Heat power measurement is well created into miniaturized structures. The manufacturing of suitable heat power transducers like integrated thermopiles, thin film thermistors or platinum resistors and miniaturized heaters for calibration purposes are possible on high technological standard. This paper represents the results from measurements with miniaturized calorimeters.

J. Lerchner, R. Oehmgen, G. Wolf

### Heating and Calorimetry in Single Droplets and Micro Fluid Reactors

The authors present four different devices prepared by means of micro machining technique incorporating different concepts and materials, feasible for heating of and calorimetry in liquid flows at low rates of up to 1 ml/min or in single droplets of 1–50µl. The heat management and calorimetric data are strongly determined by the used materials, the device topology, and the geometrical arrangement of heaters and sensing elements.

Martin Zieren, Gudrun Steinhage, Torsten Schulz, Volker Baier, Ulrich Dillner, Karl Cammann, John Michael Koehler

### Microreactions on the Surface of an Oligonucleotide Bearing Chip

Plain surfaces with suitable chemical functions at defined positions are prepared. The handling of such kind of microreactors is simplified enormously since many probes defined by their chemical nature and their position are treated simultaneously. However the reaction products are different depending on the immobilized probe. Enzymatic reactions are becoming a valuable tool in order to achieve high specifity and efficiency. Typical reactions in molecular biology such as hybridization and nuclease digestion have been carried out on the surface of on oligonucleotide bearing chip. The density of molecules immobilized onto the surface influences the efficiency of the desired reaction. Gelatine as the main component of the immobilization matrix proofed to be a suitable material to set up a micropatterned multi functional immobilization matrix.

Eugen Ermantraut, Klaus Wohlfart, Stefan Wölfl, Torsten Sculz, J. Michael Köhler

### Coulometric Nanotitrators with Potentiometric Endpoint Detection

Coulometric nanotitrators are reported and their applications for different types of titrations are described. Detection of the titration endpoints was carried out by a potentiometric method. Precipitation, complex-formation, redox and acid-base nanotitrations were realized. The results show a linear dependence between 10−2 to 10−3 M or less of analyte.

O. T. Guenat, Ph. Arquint, W. E. Morf, B. H. van der Schoot, N. F. de Rooij

### Miniaturization as a Demand of High-Throughput Synthesis and Analysis of Biomolecules

The catchphrases biotechnology, combinatorial chemistry and high-throughput-screening are implementing the need for automation and miniaturization in order to handle thousands of different substances within a short limit of time and a minimum consumption of valuable biomolecules. Automation and miniaturization of chemical and biological reactions like combinatorial synthesis, polymerase chain reaction (PCR), or DNA-sequencing require high numbers of one-way tools for synthesis, separation and analysis. Such consumables can be microstructured in a variety of materials including glass, polymers, metals, and silicon, generating structures with high aspect ratios and dimensions in the low µm-range, which in the case of polymers can be injection-molded. The present paper describes several miniaturized components and integrated systems for the application mentioned above.

R. Konrad, W. Ehrfeld, H. Freimuth, R. Pommersheim, R. Schenk, L. Weber
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