2-layer microfluidic system

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. 

The earlier work on mica pores gave strong support to the hypothesis that the viscosity was a local property of liquids down to the molecular level. Supporting this result were some of Israelachvili s studies on shearing of layers several molecular distances thick. Because of the potential importance of microfluidic systems, several studies were initiated to examine fluid flow in micrometer scale ducts. Photolithographic microfabrication was used to make channels with D/, as small as 1 /zm. For these dimensions. Re is quite small and so is the volumetric flow. To put the point more finely, consider the case of a triangular microchannel with Z A = 10 /zm, L = 10 mm, and A/ = 10 kPa. Using equation (12.4) with o,he(,r = 13.30, the volume flow for water is of the order of 160 /u-1 day" ... 

In a similar effort to combine preconcentration with electrophoretic separations, Fortier et al. [123] investigated the analytical performances of a microfluidic system comprised of an enrichment column, a reversed phase separation channel, and a nanoelectrospray emitter embedded together in polyimide layers. The authors demonstrated that the configuration minimized transfer lines and connections and reduced peak broadening and dead volumes, resulting in good reproducibility of retention time and peak intensity. The microchip was interfaced to both ion trap and TOF MS. Measurements were performed for a dilution series of protein digests spiked into rat plasma samples and provided an LOD of 1-5 fmol. 

Another relevant issue for sensors is packaging. In particular, for chemical sensors designed for working in solution, it is necessary to prevent the solution from any contact with the semiconductor layer (if this is not the sensitive layer of the device). Microfluidic systems [35,36] coupled with the sensor s active areas offer a valid solution to this problem because they allow the flow of the solution to the active area to be controlled and channeled, without compromising the semiconductor layer. For pressure/strain sensors the packaging should not compromise the mechanical flexibility of the whole structure. 

In addition to major organs, such as a heart, lung, and liver, kidney- [30], splenon-[85, 86] and breast- [87] on-a-chip devices have been developed. Fig. 9 shows the schematics of these three devices. Kidney-on-a-chip devices include a porous membrane where kidney cells and epithelial are cultured in each side. This membrane, which is similar to the one used in the lung-on-a-chip device, consists of the central channel and two sub-channels—an apical luminal channel and a basal interstitial space. Compared to the traditional microfluidic system, the exposure of the epithelial cell layer to the certain shear stress generated by inflow mimics the in vivo kidney tubules, resulting in promotion of epithelial cell polarization and primary cilia formation. This platform is useful for the study of kidney toxicity during drug development. 

It is known that glass cannot be anodicafly bonded to glass. However, research has found that this can be realized by depositing an intermediate layer. The intermediate layer can be polysilicon, amorphous silicmi, silicon nitride, or silicon carbide [9]. This has opened an easy route to constmct glass-based microfluidic systems which are widely used for capillary electrophoresis. Other investigations into anodic braiding have... 

In microfluidic systems, due to the very thin EDL compared to the microchannel dimension, the electroosmotic velocity distribution and EDL potential profile inside the EDL region become insignificant. Thus we do not need to solve the Poisson equation together with the Boltzmann distribution. Instead the electroosmotic flow velocity at the edge of the EDL (i.e., from the diffuse layer to the bulk phase) is given by the Smoluchowski equation [1], expressed as... 

Biological macromolecules are often handled through microfluidic systems, in which these molecules can transport and react. A common driving force behind such microfluidic transport processes is the electrokinetic force, which originates as a consequence of interaction between the electric double-layer potential distribution and the applied electric field. This entry discusses some of the important features of the biochemical reactions in such microfiuidic systems. 

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