Bio-MEMS - Bio-MEMS For Diagnostics - PCR Chips

PCR Chips

The polymerase chain reaction (PCR) is a fundamental molecular biology technique that enables the selective amplification of DNA sequences, which is useful for expanded use of rare samples e.g.: stem cells, biopsies, circulating tumor cells. The reaction involves thermal cycling of the DNA sequence and DNA polymerase through three different temperatures. Heating up and cooling down in conventional PCR devices are time-consuming and typical PCR reactions can take hours to complete. Other drawbacks of conventional PCR is the high consumption of expensive reagents, preference for amplifying short fragments, and the production of short chimeric molecules. PCR chips serves to miniaturize PCR into microfluidic bio-MEMS and can achieve rapid heat transfer and fast mixing due to the larger surface-to-volume ratio and short diffusion distances respectively. The advantages of PCR chips include shorter thermal-cycling time, more uniform temperatures during the PCR process for enhanced yield, and portability for point-of-care applications. Two challenges in microfluidic PCR chips are PCR inhibition and contamination due to the large surface-to-volume ratio increasing surface-reagent interactions. For example, silicon substrates have good thermal conductivity for rapid heating and cooling, but can poison the polymerase reaction. There are stationary (chamber-based), dynamic (continuous flow-based), and microdroplet (digital PCR) chip architectures.

  • Chamber-based architecture is the result of shrinking down of conventional PCR reactors, which is difficult to scale up. A four-layer glass-PDMS device has been developed using this architecture integrating microvalves, microheaters, temperature sensors, 380-nL reaction chambers, and capillary electrophoresis channels for reverse transcription polymerase chain reaction (RT-PCR) that has attomolar detection sensitivity.
  • Continuous flow-based architecture moves the sample through different temperature zones to achieve thermal cycling. This approach uses less energy and has high throughput, but has large reagent consumption and gas bubbles can form inside the flow channels.
  • Digital PCR eliminates sample/reagent surface adsorption and contamination by carrying out PCR in microdroplets or microchambers. PCR in droplets also prevents recombination of homologous gene fragments so synthesis of short chimeric products is eliminated.

Read more about this topic:  Bio-MEMS, Bio-MEMS For Diagnostics

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