Polydimethylsiloxane microchannel

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. 

More recently, Sugiura et al.11 developed a fully functional microvalve based on this photoresponsive behavior, which was composed of poly(/V-isopropylacrylamide) functionalized with the chromophore spirobenzopyran (pSPNIPAAm). The microvalve was fabricated in a polydimethylsiloxane (PDMS) microchannel by in situ photopolymerization. Blue light irradiation (18 to 30 s) to the gel induced photoisomerization of the spirobenzopyran chromophore which resulted in shrinkage due to dehydration of the gel, thus causing the microvalves to open, as seen in Figure 23.7. In this example, localized irradiation enabled independent control of three photoresponsive polymer gel microvalves, which had been fabricated on a single microchip. 

Sundararajan N, Pio M, Lee L, Berlin A (2004) Three-dimensional hydrodynamic focusing in polydimethylsiloxane (PDMS) microchannels. J Microelectromech Syst 13(4) 559-567 Yang R, Feeback D, Wang W (2005) Microfabrication and test of a three-dimensional polymer hydro-focusing unit for flow cytometry applications. Sens Actuators A Phys 118(2) 259-267... 

Microchannels created using dry etching techniques on silicon-based substrates often have a cross section that is close to a rectangle. This geometry is also common in polymer-based microchips, e.g., created using PDMS (polydimethylsiloxane) material, which are popularly used in the research commxmity due to their simpler fabrication procedure. The effect of the rectangular geometry on the hydrodynamic... 

In a typical microfluidic setting, the most power absorbing material is the liquid sample in the microchannels. The common materials for microfluidic chips are glass, quartz, and thermal plastics such as polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA), and polycarbonate, which usually have very small absorption as compared to liquid materials. The absorption of the liquid medium increases with its ionic content which increases the conductivity and with the operating frequency. Take water as an example. 

Printed circuit board (PCB) technology was employed for the fabrication of electrodes to be employed for luminol-H202 solutions. These electrodes were used with two microfluidic ECL cells that combine transparent polydimethylsiloxane (PDMS) microchannels [16]. The differences between the two cells were the working electrode size (10 mm Au vs 0.09 mm Au) and the ECL detection volume (4 pL vs 4 nL). No counter electrode was used in this system while Ag/AgCl reference electrode was obtained by electrodeposition of Ag on Au,... 

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. 

A final approach to integrating microdialysis membranes with microfluidics is based on direct bonding of microdialysis membranes with the microchannel stmctures. One such structure was developed by Bohn and colleagues [12] and is shown in Fig. 4c. Here microchannels are defined in polydimethylsiloxane (PDMS) in the soft lithography pro-... 

BH J, Van Lerberghe LM (2000) Three-Dimensional MicroChannel Fabrication in Polydimethylsiloxane (PDMS) Elastomer. J Microelectromech Syst 9(1) 76-81... 

PDMS (PolyDiMethylSiloxane) - transparent silicone elastomer MicroChannel molded in PDMS Polypyirole Gold Electrodes... 

---