Battery-operated portable PCR system with enhanced stability of Pt RTD

This paper reports an outdoor-use polymerase chain reaction (PCR) technology in which stability of resistance temperature detectors (RTDs) is remarkably improved. A thin-film RTD made of non-annealed Pt shows accuracy degradation because the resistance of the RTD tends to decrease during the PCR operation. Thus, the annealing process is applied to the Pt RTD to improve the stability, which is a prerequisite to the accurate measurement of the absolute temperature. Both heaters and the RTD are fabricated on a thin quartz substrate whose melting temperature is high enough for annealing. The performances in the PCR time and power consumption are enhanced by reducing the size of the heater chips with no degradation in the temperature uniformity. A spring-loaded electrode is employed to simplify the procedure of electrical connection to the thermal controller and loading/unloading of the PCR chip. The contact area of the electrical connection is so small that the conductive thermal resistance increases; thereby small heat dissipation can be exploited for low-power operation. The stability of the RTD is experimentally confirmed in terms of resistance variation over repeated PCR operations (four times). The least variation of 0.005%, which corresponds to a negligible temperature variation of 0.038 °C for the PCR, is achieved from the RTD annealed for 5 min at 450 °C. The gel-electrophoresis result indicates that the PCR performance of the proposed system using a film-type PCR chip is comparable to that of a conventional system using a vial tube despite its low power consumption.