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

Abstract

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.

Fig 1. Schematic of the PCR system with a dual heater chip with an RTD, dual fans, a PCR chip, a control board, an LCD touch screen, and a battery.

Fig 2. Design of a Pt heater chip with an RTD.

Design of Pt heaters and meander pattern RTD (a), sandwiched arrangement between heater chips and a PCR chip (b, c).

Fig 3. Schematic image of a film-type PCR chip.

Exploded layers of the PCR chip (a) and dimensions of the PCR chamber pattern (b).

Fig 4. Three-dimensional schematic of the conduction module including dual heater chips, a PCR chip, pin-type electrodes, and positioning frames (a), pin-type electrode with a spring (b), front-view image describing the direction of air flow from the dual fans (c), and side-view image (d).

Fig 5. Simulated temperature distribution of the PCR chip by COMSOL Multiphysics.

Fig 6. Fabrication sequence of the heater chip with an RTD (a), fabricated heater chip (b), enlarged view of the Pt RTD (c), and fabricated PCR chip (d).

Fig 7. Entire PCR system with dual Pt heaters, dual fans, a stabilized Pt RTD, a controller, and a battery (total size: 210 mm × 170 mm × 230 mm).

Fig 8. Resistance degradation of the non-annealed Pt RTD during four times of the PCR operations.

Fig 9. Resistance change versus number of the PCR operations.

Fig 10. Gel-electrophoresis result of the amplified genomic DNA band of E. Coli bacteria.

The electrophoresis result of the PCR using the non-annealed RTD (a), annealed RTD (b), and comparison with the conventional PCR system (c); Lanes 1, 4, and 6: ladder marker, Lanes 2 and 3: thin-film heater with the non-annealed RTD, Lane 5: thin-film heater with the annealed RTD with high annealing temperature (60 °C), Lane 7: Pt thin-film heater and RTD PCR system, and Lane 8: conventional PCR system.