Polydimethylsiloxane microreactor

Index Entries Microscale bioreactor polydimethylsiloxane microreactor immobilized enzymes urease enzyme silicon wafer. 

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of >90% were observed. 

In this article, we report on the fabrication and performance of microreactors constructed of silicon and polydimethylsiloxane (PDMS). The resulting structures contain immobilized enzymes for converting biochemical substrates to useful products or for breaking down organics into waste streams. 

Fig. 32 Flow microreactor system consisting of a polydimethylsiloxane (PDMS) multilayered laminar micromixer and PTFE microtubes for polymerization of amino acid A-carboxyanhydride (NCA) initiated by triethylamine...

In addition to these organic syntheses, biochemical production of compounds in microreactors has also been performed. A microreactor array which enables high-throughput cell-free protein synthesis was developed [4]. The microreactor array is composed of a temperature control chip and a reaction chamber chip. The temperature control chip is a glass-made chip on which temperature control devices, heaters, and temperature sensors are fabricated with an indium tin oxide (ITO) resistive material. The reaction chamber chip is fabricated by micromolding of polydimethylsiloxane (PDMS)... 

There are a number of materials used for the fabrication of pTAS devices. Perhaps the most common is glass due to its low cost, ease of machining, and suitability for electrophoresis and electroosmotic flow (EOF) applications without requiring surface modifications. It is also chemically inert to most reagents (apart from hydrofluoric acid and concentrated alkali). Silicon is also a valuable material that has similar chemical inermess and can easily be machined by chemical etching. While it is more expensive, it can be easily chemically etched to yield far higher aspect ratios than are possible with glass. Silicon is not suitable for electrophoresis or EOF applications without surface pretreatment. Devices fabricated from polymers such as polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) are also frequently used due to the low cost of the material (especially important for disposable devices) and the ease of fabrication. Perhaps one drawback with polymers is their incompatibility with solvents. They are suited to electrophoretic applications but frequently require surface modification to support EOF. Occasionally, metals are used however, these are far more frequently encountered in chemical microreactors. 

Maeda et al. examined intramolecular [2 + 2] photocycloadditions of 1-cyano-naphthalene derivatives (I) in microchannel reactors [4]. They use microreactors made of polydimethylsiloxane (PDMS) and Pyrex glass. With a photolithographic method, channels of 300 pm width, 50 pm depth and 45-202 mm length are fabricated. For the photoreaction (Scheme 16.2), flow rates of 0.03-0.005 mLh are applied and a xenon lamp with a UV-29 Alter (> 290 nm) is used as a light source. The authors report that under the conditions prevailing in the microreactor, higher regioselectivity and efficiency are achieved compared with batch process conditions. 

Cell-free protein synthesis was performed using polydimethylsiloxane (PDMS)-based microreactor arrays [22]. The microreactor array chip comprised a temperature control chip made of glass and a disposable reaction chamber chip made of PDMS. To evaluate the performance of this microreactor array, rat adipose-type fatty acid binding protein, glyceraldehyde-3-phosphate dehydrogenase, cyclophilin, and firefly luciferase were synthesized from their respective DNA templates using a cell-free extract prepared from Escherichia coli. 

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