Capillary-Based Microfluidics

Reoples, M. C., Rhillips, T. M., and Karnes, H. T., A capillary-based microfluidic instrument suitable for immunoaffinity chromatography. Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences 843(2), 240-246, 2006. 

Chang et al. [5] utilized microtubes to generate micro-segmented flow. Upon surface modification, the prepared nanoparticles were mixed with a monomer and emulsified into uniform droplets in a capillary-based microfluidic device. The microchannel-based reactor offered reliable control over the nanocomposite products by precisely adjusting the interfacial tension. 

Capillary-based microfluidics Hydrophobic/ hydrophilic microfluidics Surface tension-confined microfluidics Wetting on stmemred substrates... 

Surface tension-confined confined microfluidics Wetting on structured substrates Capillary-based microfluidics Hydrophobic/hydrophilic microfluidics... 

Figure 10.3 shows the IR-LDI mass spectrum of the peptide bradykinin (Mr = 1060.2) desorbed and ionized from the PDMS cover. The bradykinin was loaded into the chip at a concentration of 2.5 mM and injected into the chip channel using a field of 150 Y cm-1 for 9 min. The spectrum is the result of 10 laser shots at 2.95 pm wavelength. The off-line capillary gel microfluidic mass spectra are obtained after electrophoretic transport through a closed chip channel. Operation with a closed channel requires that the cover be removed from the chip prior to analysis. When removing the cover, sections of the gel tended to adhere to the surface of the PDMS. With some amount of care the entire gel lane could be extracted intact from the chip and, in many cases, irradiation of the PDMS cover resulted in the best mass spectra. The base peak... 

UV absorbance can easily be done on capillary-based systems using capillaries at least 50-75 pm in diameter. It is a universal method of detection that can be used with high sensitivity with most analytes. The short pathlength provide by the shallow channels make UV absorbance detection difficult to implement on microfluidic systems. In addition, microchip-based systems fabricated from glass instead of fused silica absorb significant amounts of UV, further complicating its implementation. In future experiments, detection methods may include direct conductivity measurements (microchip-based SCCE) and contactless conductivity methods (capillary-based SCCE). 

By droplet-based microfluidic techniques, spherical microparticles can be produced. In this process, a polymer solution or a two-component system is separated by an inert nonmiscible fluid to obtain droplets in the 10-200 om range. In most cases, spherical particles are obtained however, also rods or ellipsoids have been realized [108]. For droplet miCTofluidics, either glass capillary devices can be used or devices made by lithography techniques, commonly consisting of PDMS. Figure 3.69 shows a flow scheme for the... 

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... 

As glass and quartz exhibit the same surface property as fused-silica capillary, the monolithic materials could be conveniently prepared in a glass- or quartz-based microfluidic device via the same way of monoliths in the capillary. However, glass/quartz devices are rather expensive, and the need for specialized facilities for their fabrication with conventional photolithography technology hinders any rapid modification of the chip architecture. An attractive alternative is using a variety of polymeric materials, such as poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and cyclic olefin copolymer (COC), to fabricate microchips for their mechanical and chemical properties, low cost, ease of fabrication, and high flexibility. 

In capillary-based chemical cytometry, a cell is injected into a capillary, where it is lysed, and then its contents are separated by electrophoresis. The separating contents are detected at or near the end of the capillary, as the analytes migrate past the detection zone. Microfluidic devices are well suited to replace capillaries for chemical cytometry. The channel dimensions (5-100 pm) and planar geometry allow for very efficient dissipation of Joule heat produced from large electric field gradients. The capacity to apply high fields (e.g., 500-1,000 V/cm) dramatically reduces separation time and minimizes band diffusion. Most importantly, the small channel dimensions can handle injection volumes ranging from nanoliters to himdreds of femtoliters [18] and thus result in minimal dilution of sample. 

Fang, Q., Wang, F.-R., Wang, S.-L., Liu, S.-S., Xu, S.-K., and Fang, Z.-L., Sequential injection sample introduction microfluidic-chip based capillary electrophoresis system, Anal. Chim. Acta, 390, 27, 1999. 

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