a miniaturized temperature - zone flow reactor , used for thermally controlled biochemical or molecular - biological processes , especially polymerase chain reaction enables more efficient reactions by providing at least one closed flow path which is divided into three partial paths with the reactor having three substrate chips which are made of a material having a high heat conductivity , and which have defined channel sections that are spaced apart relative to each other , and are connected by a connecting chip made of a poor heat - conductive material . the substrate chips are maintained at different temperatures by various means , including the use of controlling heating elements in contact with the chips .