Temperature Control of a Droplet Heated by an Infrared Laser for PCR Applications
Zhibin Wang, Xingguang Liang, Hongshi Su, Shiyi Li, Ying Chen
Abstract
Temperature control is one of the essential operations in droplet-based microfluidics. Light based on the photothermal effect is very suitable to heat a droplet because of noncontact and local heating. However, it is unable to predict the droplet temperature precisely. This paper reports an infrared laser to heat a droplet in a microchannel based on the photothermal effect for temperature control. The numerical method is applied to simulate the thermocapillary flow and heat transfer of this heating process. Particular attention is paid to the impact of laser beam size and input power on the droplet’s temperature distribution, heat transfer, and thermocapillary flow. The results show that increasing the laser power and decreasing the laser beam size increase the average temperature and thermocapillary flow due to the increase in the actual absorbed energy. The heat transfer coefficient of the droplet interface increases with the decrease of the laser beam size due to weakening of thermocapillary flow. It is also found that the nonuniform temperature coefficient reduces when the input power and the laser beam diameter increase, and the expression of the average temperature increase is obtained by considering the effects of the laser power and the laser beam diameter. With the obtained expression of the average temperature, a thermal cycle of polymerase chain reaction (PCR) amplification, a laboratory technique used to make multiple copies of a segment of deoxyribonucleic acid (DNA), can be successfully obtained. The results of this work will provide support for temperature control and applications, such as PCR amplification, in droplet-based microfluidics.