Numerical simulations to analyze the effect of various heater configurations on heat transfer in polymerase chain reaction devices

Abstract

Polymerase chain reaction (PCR) is used to amplify small amount of Deoxyribonucleic Acid (DNA). It has been used extensively in biomedical laboratories and has become a powerful tool for clinical, medical diagnostic, biological, forensic and genetic analysis and other areas of life science. This process actively increases the amount of DNA by repetition of three step procedure which includes denaturation, annealing and extension, which are to be performed at 95°C, 72°C and 55°C respectively. These temperatures are maintained by attaching the heaters in the denaturation, extension and annealing zones of PCR device. In the proposed design the PCR channel is embedded in a glass substrate which is a solid domain and conduction being the dominant heat transfer phenomena in a device. Heat flows from high temperature region to low temperature region during conduction, making it difficult to maintain the constant temperature zones in the solid domain which is a necessary requirement to avoid thermal cross talk between the zones. Multiple methods are proposed in the literature for this purpose. They include use of insulation materials, creation of air gaps between the three zones, and the use of two heater configurations with cooling jackets to maintain constant temperature in the middle zone. In this work, three-dimensional heat transfer plus computational fluid dynamics (CFD) simulations are performed to study the temperature distribution and heat transfer characteristics in a continuous flow glass based PCR device using three and one heater configurations. Three heaters of constant temperature are attached to the lower surface of the glass substrate and a comparison of temperature distribution along lateral direction is carried out for 8mm and 9mm heater lengths. Then one heater configuration is used in such a way that there is a thin sheet made of invar and is placed between the heater and the PCR device. The temperatures in the zones without heaters are controlled by fluid convection phenomena. The comparison of residence time for both configurations shows that the residence time is independent of number of heaters and the temperature distribution in a PCR channel. The study provides a useful comparison between different heater configurations and their effect on heat transfer in polymerase chain reaction devices.