Glass/PDMS hybrid

Electrochemical detection was easily employed for the determination of uric acid in urine, abnormal concentrations of which have been linked to several disease states [14]. A glass/PDMS hybrid device with an off-chip platinum electrode was used to evaluate standard samples for both dopamine and uric acid. The linear responses for dopamine and uric acid were 1-165 and 15-110 pM, respectively, with a 1 pM limit of detection for both. Normal concentrations of uric acid in urine are 800-8000 pM, thus a 50 to 75-fold dilution was used with the urine samples analyzed to place them within the linear range of the detection method. Uric acid concentrations in these urine samples were confirmed using the clinically accepted method. This new method should allow clinical detection of both abnormally high and abnormally low uric acid concentrations in urine samples on a microdevice. 

Glass/PDMS hybrid microchip Trypsin Covalent linking Trypsin covalently immobilized onto poly(acrylic acid) plasma-modified surfaces for membrane proteomics analysis [80]... 

Very recently, Wilkes and co-workers 330,331) have reported the preparation and characterization of hybrid materials, which they named as ceramers . Ceramers were synthesized through the incorporation of polymeric or oligomeric PDMS into silicate glasses by a sol-gel process as shown in Reaction Scheme XXIV. During these reactions the variables such as the type of the alkoxide used, amount of water added, the pH value of the reaction system, and the reaction temperature, were carefully monitored. 

Hydroxy-terminated PDMS, however, has disadvantages. The monofunctional ends limit the number of connections between the polymer (or oligomer) molecule and the glass network to two. This limitation raises the possibility that some PDMS molecules are not tied at both ends to the glass network if the polycondensation does not go to completion i.e. there may be "dangling" or loose PDMS chains in the final sol-gel material. This occurance of free ends would indeed be anticipated since the extent of reaction most likely is not 100%. Hence, the physical properties, specifically the mechanical behavior of the overall material, would be expected to suffer as a result of loose PDMS chains in the system. Disregarding this potential problem, the mechanical behavior of the sol-gel hybrids are, ultimately, influenced by the mechanical behavior of the modifying elastomer ... 

For PDMS-modified Si02 glasses, structural analysis shows that this hybrid material has some degree of localized phase separation of the PDMS component, even though OH-terminated PDMS can be successfully incorporated into the Si02 network by chemical bonding. The PDMS component can behave as an elastomeric phase because the glass-transition temperature of PDMS is far below room temperature.52 54... 

A small magnetic stirring bar (2 mm dia. x 7 mm) was used to enhance mixing in a PDMS-glass chamber (50 iL). This led to a three- to four fold increase in the DNA hybridization efficiency [490],... 

DNA hybridization in microchannels has also been conducted in the low-density microarray format. For instance, DNA hybridization was carried out in 32 chambers each spotted with 16 DNA probes for the detection of bacteria (e.g., Campylobacter jejuni, E. coli) on a PMMA/PDMS-glass chip. PDMS was used as a bonding layer to seal the PMMA plate onto the glass microarray plate [963]. 

In another report, DNA probes were spotted on a glass plate, which was then aligned and covered by the PDMS channel plate for hybridization to occur [964]. 

FIGURE 1 (A) The image of an assembly of a 2" x 2" PDMS channel plate on a 3" x 2" glass slide. The 16 channels filled with blue-dye solutions. (B) Dual-channel fluorescent images of DNA hybridization results with the 2D microfluidic microarray method. The overlaid images from the same glass slide show both printed probe lines (vertical green lines) and square hybridization patches (red) at intersections. Used with permission from Dupuy and Simon (5). 

To address this we have recently developed unique optofluidic based on chip SERS devices. The chip exploits our previously developed electro-active microwells [11] which are used here to enhance mixing for DNA hybridization and concentration for sample enrichment (Fig. 7). The chip comprises of a glass substrate with lithographically patterned electrodes. The substrate and electrodes are covered with an electrically insulating polyimide layer into which 10 pm diameter wells and microfluidic system are etched. After completion we align and bond the PDMS cover to the bottom substrate such that the wells align with the spaces in the upper electrodes. 

Instead of merely exploiting microscale physical phenomena using simple straight-channel patterns with constant cross section, it is certainly feasible to make use of well-developed microfabrication methods for introducing flow control functionality into individual components. Although various MEMS approaches have been utilized for this purpose (as reviewed by Oh and Ahn ), many of these techniques require complex fabrication and will not be discussed here. This section focuses on more practical passive components that can be fabricated in PDMS or PDMS-glass hybrid devices, requiring minimal fabrication complexity in addition to the typical microchannel assembly methods. 

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