The thermal cycling methods for rapid PCR

Polymerase chain reaction (PCR) is a critical technology in nucleic acid detection and quantification. The PCR reaction requires thermal cycling the reaction mixture between two or more temperature stages for ∼30 cycles to achieve exponential amplification of the target DNA. Typically, the thermal cycling takes roughly an hour to finish and the large time consumption is a drawback for PCR. We review the various methods developed to reduce the thermal cycling time and build a rapid PCR. We group the methods to two approaches. The first approach is to increase the local heating/cooling power. The methods in this approach include contact heating, such as: heating resistors and Peltier pumps, and non-contact heating using air-blow, radiation on water and plasmonics. The other approach is to rapidly move the reaction mixture to a different temperature zone. Methods in this approach include: relocating the reaction vessel, continuous flow PCR using microfluidic chips, long tubes or oscillatory PCR scheme, and convective PCR. We analyze the advantages and challenges for each method used and the critical parameters to consider when evaluating the technologies. We review the technological advances and commercialization for each method. We also discuss the current challenges and future directions in building an effective and commercial rapid PCR, with the emphasis on sensitivity, portability and cost.