Polymerase chain reaction
Break out the bubbly: Avoiding air bubbles in PCR microdevices
The emergence of microfluidic PCR devices is one of the most important recent developments in the field of PCR. One of the remaining challenges in this area, in particular for the performance of continuous-flow PCR microdevices, is the circumvention of air bubbles that are generated by high temperatures during the initial startup of thermal cycling protocols. A simple solution to this problem now appears to be at hand.
The availability of effective continuous-flow components for DNA amplification would facilitate the development of micro-total analysis systems (?TAS), which integrate several different microfluidic devices to carry out different functions, from sample preparation to signal quantification. To achieve this, the initial startup flow of the sample solution would need to be stabilised in such a way so as to avoid air bubble formation at the liquid front as it moves though microchannels subjected to increasing temperatures.
Progress in this area was recently reported in Analytical and Bioanalytical Chemistry by a team led by Eiichi Tamiya, of the School of Materials Science at the Japan Advanced Institute of Science and Technology in Ishikawa, Japan. Using continuous-flow microfluidic devices fabricated by standard soft-lithography techniques from polymethylsiloxene (PDMS), the group investigated the effects of applying an inert and highly viscous fluorinated oil immediately prior to the introduction of the sample solution.
By increasing the pressure of the assay liquid (and also due to its high boiling point), the introduction of the fluorinated oil was able to prevent the formation of air bubbles at the sample front. This novel modification enable the effective use of these continuous-flow microdevices for PCR, even in combination with on-chip laser-based detection of DNA amplification, as demonstrated by the amplification of and quantification of a marker sequence for GM maize.
With this successful demonstration of quantitative PCR in a continuous-flow microfluidic device, the expectation arises that such microdevices may soon become part of the standard equipment repertoire for point-of-care diagnostics.
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