Monday, 20 December 2010

Advances in polymerase chain reaction

Simplifying PCR – or Polymerase Chain Reaction, a biotechnology technique used to replicate a specific portion of a much larger sample of DNA - and the related instrumentation could enable advances in both clinical and basic research as well as expand the number of places where molecular biology diagnostic testing could be performed.

Reporting in the January 2011 issue of BioTechniques, researchers from the National Taiwan University in Taipei describe their development of a new PCR system that requires only a capillary tube and a single isothermal heating unit.

“One day we came across the idea of trying to run the PCR reaction in a vertical plane—instead of a horizontal plane—to improve flow speed,” said Pei Jer Chen, senior author of the report.

Many groups have designed microfluidic-based PCR devices to speed reaction times and minimize reagent consumption. But Chen and his team hypothesized that natural convection within a capillary tube might create the necessary conditions to mix and circulate PCR reagents without the need for the complicated channels and expensive pumps required in many microfluidic devices.

The real surprise for the authors, however, came from the finding that the thermal convection created within a capillary tube was not only capable of circulating both the reagents and the DNA from the bottom of the tube to the top, but as the samples passed through different temperature zones within the capillary tube during convection, these temperature changes led to DNA amplification without the need for expensive heating elements and thermal control devices.

“We almost could not believe this,” said Chen, “as we have painstakingly tried for years to design and manufacture microfluidic chips for PCR without similar success.” Chen’s team demonstrated that their convection-based PCR system is capable of amplifying lengths of DNA up to 500 base pairs in under 30 minutes with a sensitivity of 30 copies per reaction, using a single constant heating source.

While convection PCR could be adopted by any lab right away by using a common heating plate, Chen and his colleagues hope their system can be implemented as a point-of-care device in the future. “This platform has that potential, as the heating unit only needs powering from batteries or another convenient energy source,” he noted. Chen is now working to advance the readout procedures for his system to enable simple, rapid detection of an amplification product, another key step in developing a point-of-care diagnostic device for use in remote locations around the globe.

The article, “Rapid DNA amplification in a capillary tube by natural convection with a single isothermal heater” can now be found online at or at