Glass-based microchips, microchip

Normally, the glass-based microchips have good performance because the surface property is similar to the inner surface of conventional capillaries and high optical transparency. The samples are normally loaded by EK injection and detected with UV or LIF detectors positioned at the end of the channel. In recent years, companies such as Agilent, Hitachi, and Shimadzu have developed equipment based on microchip technology for biochemical analysis, and such equipment is now commercially available (16). 

M.J. Schoning, M. Jacobs, A. Muck, D.-T. Knobbe, J. Wang, M. Chatrathi and S. Spillmann, Amperometric PDMS/glass capillary electrophoresis-based biosensor microchip for catechol and dopamine detection, Sens. Actuator B, 108 (2005) 688-694. 

We recently described the first example of EC detection in PDMS-based microchip CE devices using a device similar to that depicted in Figure 8 [58]. Multiple gold electrodes were deposited on the glass substrate that was then covered with the PDMS separation channels. For dual electrode detection, two of these electrodes were used. The microchip format is ideal for multiple electrode detection in CEEC because it is much simpler to construct and align electrodes at the end of a planar ehannel than to reproducibly place two electrodes at the end of a fused silica capillary. 

FiGURE 5.7 Schematic diagram of the microchip FI-CE amperometric detection device used. C fused-silica capillary S planar glass base G epoxy F conical inlet L liquid phase X glass plug A air bubble T Tygon tube P platinum anode N platinum cathode. (Reprinted from Fu, C.-G. and Z.-L. Fang, 2000. Anal. Chim. Acta 422 71-79. With permission.)... 

Guijt et al. [69] reported four-electrode capacitively coupled conductivity detection in NCE. The glass microchip consisted of a 6 cm etched channel (20 x 70 pm cross-section) with silicon nitride covered walls. Laugere et al. [70] described chip-based, contactless four-electrode conductivity detection in NCE. A 6 cm long, 70 pm wide, and 20 pm deep channel was etched on a glass substrate. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection set up. Jiang et al. [71] reported a mini-electrochemical detector in NCE,... 

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. 

An active mixer based on an oscillating EOF induced by sinusoidal voltage ( 100 Hz, 100 V/mm) was devised and modeled for mixing of fluorescein with electrolyte solutions. This is termed as electrokinetic-instability micromixing, which is essentially a flow fluctuation phenomenon created by rapidly reversing the flow. Various microchips materials (PDMS, PMMA, and glass) and various electrolytes (borate, HEPES buffers) have been used to evaluate this method of micromixing [480]. 

Besides the commonly used direct LIF detection, indirect LIF detection on the microchip has also been reported. This method has been employed to detect explosives in spiked soil samples (see Figure 7.9) [620]. In contrast to a capillary-based system, an increase in E from 185-370 V/cm for MEKC separation did not result in an unstable background fluorescence due to excessive loule heating. This was probably because of the effective heat dissipation in the glass chip. However, upon multiple injection, it was found that the detection sensitivity decreased, which might be caused by the degradation of the visualizing dye (Cy7) [620]. Indirect LIF also allows the detection of unlabeled amino acids [683]. 

Figure 10-4 Design of an asymmetric turn used in microchip-based capillary electrophoresis system constructed in glass.The design facilitates the maintenance of sample integrity during flow in a microchannel around a curve.The dimensions are indicated on the figure and are taken from the tops of the channels.The channels were filled with black ink for contrast (From Ramsey JD, Jacobson SC, Culbertson CT, Ramsey JM. High efficiency, two-dimensional separations of protein digests on micro fluidic devices.

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