the present invention provides an apparatus and method for performing heat - exchanging reactions on an electro wetting - based micro fluidic device . the apparatus provides one or multiple thermal contacts to an electro wetting - based device , where each thermal contact controls the part of the electro wetting - based device it communicates with to a designed temperature . the electrowetting - based device can be used to create , merge and mix liquids in the format of droplets and transport them to different temperature zones on the micro fluidic device . the apparatus and methods of the invention can be used for heat - exchanging chemical processes such as polymerase chain reaction and other dna reactions , such as ligase chain reactions , for dna amplification and synthesis , and for real - time pcr .