A straight-forward, inexpensive, low power continuous-flow µPCR chip using PCB-based heater electrodes with uniform temperature distribution

Abstract

A relatively high-efficiency, two-step type continuous flow microfluidic device for polymerase chain reaction (PCR) is presented in this work. The heater electrodes are designed and fabricated based on 0.25 µm-thick two-layer standard printed circuit board (PCB) technology. Temperature uniformity in different temperature zones of PCR plays a key role in increasing process efficiency. By properly designing meander shaped electrodes, relatively good temperature uniformity and high PCR efficiency is realized. A symmetrical structure is demonstrated for the arrangement of the electrodes, where the annealing electrode is placed between two denaturation electrodes. In this way, we have favorably used the thermal cross talk between the two temperature zones in order to create a relatively uniform temperature in the annealing electrode. Heat spreaders between meander lines in denaturation electrodes are used to distribute temperature uniformly, in contrast to the literature, where complex optimization methods are adopted. This eliminates the need to use bulky heat spreaders such as copper or aluminum blocks which are commonly used to uniformize temperature in continuous flow µPCRs. As a result, the number of components and the overall size of the device and consequently the complexity and fabrication cost decreases. On the other hand, the thermal mass is reduced, which in turn reduces the power consumption of the system. The temperature measurements are first performed with contact PT100 temperature sensors and then the results are verified by a thermal camera. The temperature difference measured by PT100 sensors approximately matches the standard deviation obtained from the thermal camera in a specific area. For the denaturation electrode these values are 1.14 °C and 1.2 °C, respectively. A maximum absolute temperature difference of 1 °C is measured for the annealing electrode. The fabricated microchip with dimensions of 50 mm × 40 mm is tested by an 88 base-pair DNA sample from the human housekeeping gene with a power consumption of less than 0.82 W. A relatively remarkable amplification efficiency is achieved to prove the efficacy of our inexpensive PCB electrodes.