Capillary electrophoresis on-chip

One drawback of capillary electrophoresis is the state of the capillary wall. Often, constituents of the buffer or analyte are absorbed on the sin-face, causing not only an irreproducible shift of EOF, but even the possibility of questionable binding isotherms. A lot of effort has gone into overcoming this problem. Capillaries with coated inner walls are now commercially available and capillary electrophoresis on chips of different materials is also under development now. Not only do these chips represent a miniaturized form of capillary electrophoresis, but this technique also enables the incorporation of such sample preparation steps as preconcentration and even PCR and immobilization of immunoreagents. It is not difficult to anticipate a very exciting development in this field, one with a high commercial impact. 

Lichtenberg, J., Daridon, A., Verpoorte, E., de Rooij, N.F., Combination of sample pre-concentration and capillary electrophoresis on-chip. Micro Total Analysis Systems, Proceedings of the 4th Y7AS Symposium, Enschede, Netherlands, May 14-18, 2000, 307-310. 

Manz, A., Harrison, D. J., Verpoorte, E. M. J., Fettinger, J. C., Paulus, A., Luedi, H., and Widmer, H. M. (1992). Planar chips technology for miniaturization and integration of separation techniques into monitoring systems. Capillary electrophoresis on a chip.. Chromatogr. 593, 253-258. 

Zhou et al. [175] described the determination of severe acute respiratory syndrome (SARS) coronavirus by a microfluidic chip system. The unit included an LIF microfluidic chip analyzer, a glass microchip for both PCR and capillary electrophoresis, a chip thermal cycler based on dual Peltier thermoelectric elements, a reverse transcription-polymerase chain reaction (RT-PCR) SARS diagnostic kit, and a DNA electrophoretic sizing kit. According to the authors, the system allowed efficient DNA amplification of the SARS coronavirus followed by electrophoretic sizing and detection on the same chip. 

Figure 8.22. Capillary electrophoresis on a chip, (a) Schematic of the microchip used for PCR amplification and electrophoresis. The direction of arrows indicate injection (I) and separation (S). (b) Electrophoretic microchip with multiple PCR chambers.

H. D. Widmer, Planar chips technology for miniaturization and integration of separation techniques into monitoring systems—capillary electrophoresis on a chip, J. Chromatogr, 593 (1992) 253-258. 

Fig. 3 Confocal fluorescence detection on a microchip. A laser was used as the excitation source. The laser light passed through a biconvex lens, was focused into an illumination pinhole, and was subsequently reflected by a dichroic mirror and focused in the channel on the capillary electrophoresis (CE) chip by a microscope objective. The fluorescence signal from the sample, collected by the microscope objective, was passed through the dichroic mirror, focused by the tube lens into a confocal pinhole, and then detected by a photomultiplier tube (PMT). To improve the signal-to-noise ratio, band-pass filter and notch filter were inserted above PMT for spectral filtering...

Gottschlich, N., Jacobson, S.C., Culbertson, C.T., Ramsey, J.M., Two-dimensional electrochromatog-raphy/capillary electrophoresis on a chip. Anal. Chem., 73, 2669—2674, 2001. 

Reproducible injection for capillary electrophoresis on a microdevice/Lab-on-Chip is not easy to achieve. Different injection designs (e.g., T type, double-T type, and cross type) and different injection techniques have been applied (pinched injection, gated injection, double-L injection) within microfluidic devices. The volume and the concentration of the dispensed sample are the key parameters of this dispensing process, and they depend on the applied electrical field, the flow field, and the concentration field during the injection and separation processes. The problems and properties of the different modes are described below. 

Wenclawiak BW, Puschl RJ (2006) Sample injection for capillary electrophoresis on a micro fabricated device/on chip CE injection. Anal Lett 39 3-16... 

Heegaard NHH (ed.) (2002) Paper symposium. Functional electrophoresis on chips and capillaries. Electrophoresis 23 815-977. 

Liu D.M., Chen I.W. Encapsulation of protein molecules in transparent porous sihca matrices via an aqueous colloidal sol-gel process. Acta Materialia 1999 47(18) 4535 544 Mann S., Burkett S.L., Davis S.A., Fowler C.E., Mendelson N.H., Sims S.D., Walsh D., Whilton N.T. Sol-gel synthesis of organized matter. Chem. Mater. 1997 9(11) 2300-2310 Manz A., Harrison D. J., Verpoorte E. M. J., Fettinger J. C., Paulus A., Ludi H., Widmer H. M. Planar chips technology for miniaturization and integration of separation techniques into monitoring systems—capillary electrophoresis on a chip. J. Chromoatogr. 1992 593(1-2) 253-258... 

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