Heating device, microchip

Over the past ten years, there has been an explosion of interest in the development of analytical systems in the microchip format. CE is used both to manipulate fluids and to achieve separations [4] in these devices. Very fast, highly efficient separations have been reported for such microchip CE systems. The use of CE in the microchip format allows the use of high separation field strengths (which inaeases the efficiency of the separation) because the materials typically used to construct the microchips are very efficient in dissipating heat. Most microchip CE devices have been constructed using glass [4], but devices have also been fabricated from materials such as plastics [50], low temperature co-fiied ceramics (LTCC) [51], and poly(dimethylsiloxane) (PDMS) [52]. 

Figure11.12 Microchip with integrated piezoelectric actuator and heating device (a) picture of microreactor assembly (b) schematic representation of the microreactor. (Reproduced by permission from Ref [63]. Copyright 2011, the Royal Society of Chemist. )...

The physical structures of microchip assemblies usually contain a number of thin films in contact, each of which plays a separate role in the performance of the device. As an example, in one structure a silicon thin film would be contacted on one face by a copper rod which conducts away die heat generated during computer operations, and on the other face by an aluminium thin film which acts as a connector to other silicon films. This aluminium film is in turn in contact with a ceramic layer containing other thin film devices, and widr copper pins which plug into the circuit board. 

Unlike capillary electrophoresis, wherein absorbance detection is probably the most commonly utilized technique, absorbance detection on lab-on-a-chip devices has seen only a handful of applications. This can be attributed to the extremely small microchannel depths evident on microchip devices, which are typically on the order of 10 pm. These extremely small channel depths result in absorbance pathlengths that seriously limit the sensitivity of absorbance-based techniques. The Collins group has shown, however, that by capitalizing on low conductivity non-aqueous buffer systems, microchannel depths can be increased to as much as 100 pm without seeing detrimental Joule heating effects that would otherwise compromise separation efficiencies in such a large cross-sectional microchannel [38],... 

Scheme 4.89 Two examples of microreactor loaded into a dedicated microchip and circulates PCR devices (a) Sample is continuously pumped multiple times through the temperature zones by through the flow cell and encounters different heat convection and gravity (g). Reprinted with temperature regions (resp. 55, 72 and 95 °C). permission from [383]. Copyright 2007 Wiley-Reprinted with permission from [377]. Copyright VCH Verlag GmbH.

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